Fish Sci (2012) 78:1153–1162 DOI 10.1007/s12562-012-0557-6 ORIGINAL ARTICLE Fisheries Age, growth, and reproductive characteristics of dolphinfish Coryphaena hippurus in the waters off west Kyushu, northern East China Sea Seishiro Furukawa • Seiji Ohshimo • Seitaro Tomoe • Tetsuro Shiraishi • Naoyuki Nakatsuka • Ryo Kawabe Received: 27 December 2011 / Accepted: 27 August 2012 / Published online: 13 October 2012 Ó The Japanese Society of Fisheries Science 2012 Abstract The growth and reproductive characteristics of dolphinfish Coryphaena hippurus collected in the waters off western Kyushu from May 2008 to April 2011 were determined based on scale and otolith readings and gonad histological examinations, respectively Based on annual increments in scales and daily increments in sagittal otoliths, the von Bertalanffy growth curves in male and females were determined as FLt ¼ 1049½1 À expfÀ0:835 ðt þ 6:975  10À14 ÞgŠ and FLt ¼ 938½1 À expfÀ1:029ðtþ 6:975  10À14 ÞgŠ, respectively, where FLt is the mean fork length (mm) at age t The spawning period was found to last from June to August for dolphinfish, based on an examination of the monthly changes in the gonadosomatic S Furukawa (&) Á S Tomoe Graduate School of Science and Technology, Nagasaki University, Bunkyo-machi, Nagasaki 852-8521, Japan e-mail: seishirou07@gmail.com S Ohshimo Á T Shiraishi Seikai National Fisheries Research Institute, Fisheries Research Agency, Taira-machi, Nagasaki 851-2213, Japan S Tomoe Japan Overseas Cooperation Volunteers, Japan International Cooperation Agency (JICA), Tokyo, Japan S Tomoe Service De´partemental de Peˆche et de la Surveillance de Mbour, Mbour, Republic of Senegal T Shiraishi Okayama Fisheries Promotion Foundation, Urayasu-minamimachi, Okayama 702-8024, Japan N Nakatsuka Á R Kawabe Graduate School of Fisheries Science and Environmental Studies, Nagasaki University, Taira-machi, Nagasaki 851-2213, Japan index and histological observations Therefore, based on the relationship between the fork length and the developmental stage of the testes or ovaries, male and female dolphinfish were found to reach sexual maturity by the following spawning season after hatching in the northern East China Sea Keywords Dolphinfish Á Growth Á Scale Á Otolith Á Reproduction Á Gonad histology Introduction Dolphinfish Coryphaena hippurus is a highly migratory oceanic pelagic fish found worldwide in tropical, subtropical, and temperate waters [1] In East Asia, dolphinfish support economically important recreational and commercial fisheries, and are a shared resource among multiple countries, such as Taiwan and Japan [2, 3] Dolphinfish feed on several important commercial fishery species of the East China Sea, including anchovy Engraulis japonicas, flying fish (Exocoetidae), and other small pelagic prey, including squid [4] The removal of predator biomass during commercial fishing can have profound effects on pelagic ecosystems because of the removal of predation pressure and topdown, trophic-cascade effects [5–7] Intense harvesting (i.e., overexploitation) may select for biological traits such as slow growth [8] or early maturity [9]; however, how these dolphinfish traits will change in the future remains to be determined Therefore, it is necessary to clarify the current biological characteristics of dolphinfish so that we may understand how they will change with time and how we should manage this species 123 1154 Fish Sci (2012) 78:1153–1162 Some studies of the biological characteristics of dolphinfish have been reported in several regions, and include the determination of their age and growth characteristics in North Carolina [10], Gulf of Mexico [11], and the Mediterranean [12]; their feeding habits in the eastern Pacific Ocean [13] and Mediterranean [14]; and their swimming behavior in natural conditions in the northern East China Sea [15] The reproductive characteristics of dolphinfish have been reported from North Carolina [10], the Gulf of Mexico [11], Taiwan [16], and the Gulf of Tehuantepec [17] Previous studies on dolphinfish in Japan reported their age and growth characteristics based on fork length frequency data from the Sea of Japan, and estimated spawning periods from seasonal changes in oocyte diameter [4] However, little is known about the growth of dophinfish from Japanese waters using hard parts and their reproductive characteristics using histological techniques The objective of this study was to determine age using otolith and scale readings, and to examine annual reproductive cycle and sexual maturity using histological techniques, for dolphinfish in the northern East China Sea 120 E 130 E 140 E 150 E 50 N Sea of Japan 40 N 30 N Pacific Ocean East China Sea Sea of Japan Taiwan 36 N Tsushima Islands 34 N Goto Islands 126 E 128 E 32 N 130 E 132 E Fig Sampling areas for dolphinfish in the waters off west Kyushu in the northern East China Sea Materials and methods Collections Both small and large specimens were used for aging while large dolphinfish were used for reproduction Large specimens were collected monthly from May 2008 to July 2010 (except in August 2008, April, May, September, and October 2009, and January, February, and March 2010) and in April 2011, which were caught predominantly by set net along the coast of the Goto Islands, Japan, but occasionally using troll and long line gear in the coastal waters off of Tsushima Island and the Goto Islands (Fig 1) Small specimens were caught by neuston net [18] with a mesh size of mm at sampling sites distributed in coastal waters off West Kyushu and in the Tsushima Strait in June to September 2005 The neuston net was towed through the surface water for 10 min, and specimens were sorted onboard and frozen immediately at -35 °C We did not use small specimens caught by neuston net Specimens were measured to the nearest millimeter in total length and fork length and to the nearest gram of body weight (BW) For reproductive characterization, the gonad weight (GW) was measured to the nearest 0.1 g after determining the sex, and the gonadosomatic index (GSI) value was calculated as follows: GSI ¼ GW  100: ðBW À GWÞ 123 Because dolphinfish body weight and length are correlated with GSI values and dolphinfish size varied significantly with month, GSIs were analyzed by a generalized linear model (GLM) using a gamma distribution with a log link function to test for a month effect with fork length (FL) as the covariate for males and females separately For histological observations, small pieces of the gonad were fixed in 10 % formalin Age determination For age determination, we used sagittal otoliths and scales obtained from small-sized specimens and large-sized specimens, respectively The deposition of increments in dolphinfish otoliths begins on the hatching date, and rings are laid down daily [12, 19] Thus, no adjustment was required to estimate age from incremental counts of sagittae, and it was assumed that rings were formed daily Previous studies on the microstructure of sagittal otoliths of dolphinfish from the western Mediterranean Sea had found that the daily ages of larger dolphinfish ([650 mm FL) appeared to be underestimated [12] Furthermore, in this study, daily rings of sagittal otoliths were unclear in large dolphinfish (C412 mm FL) Therefore, our daily ring determination was restricted to small dolphinfish To determine the ages of small dolphinfish in days (herein ‘‘daily ages’’), otoliths were removed under a dissecting microscope and embedded in resin on a glass slide The Fish Sci (2012) 78:1153–1162 1155 otolith increments were counted under a light microscope Since the daily rings of sagittal otoliths for large fish were unclear, sectioning and a thin polish were required However, only small fishes were used for age determination in this study, and we did not section and thin polish the otoliths to determine the daily ages of the fish Annual marks are not detectable on otoliths of dolphinfish [10] Thus, the ages of the dolphinfish in years (herein ‘‘annual ages’’) were estimated from their scales Scales were taken from above the lateral line, washed with water, and placed between two slide glasses Numbers of annual scale rings were counted under a digital microscope (E-LV100D, Nikon, Tokyo, Japan) with transmitted light The ring radii of the scales were measured using an otolith measurement system (ODRMS, RATOC, Tokyo, Japan) Each scale was examined two times, with a minimum of one month between examinations, by two independent readers If two or more examinations of the scales of the individual agreed in terms of the number of ring marks, this number was recorded and used for the analyses To validate the annual marks in dolphinfish scales, an indirect validation based on marginal increment analysis was used The marginal increment (MI) was determined using the following equation: MI ¼ ðR À rn Þ ; ðrn À rnÀ1 Þ and the growth coefficient for sex s, respectively The hypothetical age corresponding to a fork length of zero is t0 We defined FL?,s and ks in the following ways: FL1;s ¼ L1 þ L2  S; Ks ¼ K1 þ K2  s ðcase 1Þ > > > < ðcase 2Þ FL1;s ¼ L1 þ L2  S; Ks ¼ K1 ; > ðcase 3Þ FL1;s ¼ L1 ; Ks ¼ K1 þ K2  s > > : ðcase 4Þ FL1;s ¼ L1 ; Ks ¼ K1 where L1, L2, K1, and K2 are unknown constants and s is a binary parameter (if male, s = 0; if female, s = 1) We assumed that t0 is not influenced by sex, because larvae and juveniles could not be sexed, and we used FL and age data for larvae and juveniles of both sexes The variance of the fork length at age t and for sex s is given by Vðt; sÞ ¼ r20 þ r2 f1 À expðÀ2Ks tÞg; 2Ks ð2Þ where r20 and r2 represent the variance of the fork length at age and the intensity of white noise, respectively [21] The log likelihood can be represented by the following equation: " # N 1X fFLi À lðti ; si Þg2 ln L ¼ À lnf2pVðti ; si Þg þ ; ð3Þ i¼1 Vðti ; si Þ where R is the overall radius from the focus to the outer edge of the scale Rn is the radius from the focus to each annulus MIs were analyzed by a GLM using a gamma distribution with a log link function to test for a month effect where ln L is the log likelihood and i ¼ 1; 2; ; N FL?,s, ks ; t0 ; r0 and r were estimated by maximizing Eq using the gosolnp function in the Rsolnp package of R To select the best-fit model from among cases 1–4, we used the Akaike information criterion (AIC) The model which yielded the minimum AIC was selected as the best model Estimation of the von Bertalanffy growth parameters Influence of water temperature on growth The von Bertalanffy growth curve was fitted to daily ages for small dolphinfish and annual ages for large dolphinfish We could not determine the birth date of the large dolphinfish Therefore, the birth date of every large individual was assumed to be July, which approximately corresponded to the middle of the spawning period (see ‘‘Results’’) The von Bertalanffy growth parameters were estimated using maximum likelihood estimation (MLE) with the R 2.13 software package [20] (The R Project for Statistical Computing: http://www.r-project.org/) We assumed a normal distribution for fork length (FL) at age t and for sex s, with a mean of l(t, s) and a variance of V(t, s) The mean fork length at age t and for sex s is represented by the following von Bertalanffy growth equation: Asymptotic fork lengths, estimated from von Bertalanffy growth function fits using size and age data collected in different regions of the world [10, 11], were used as a regionspecific growth index We did not use the maximum size as an index for growth in order to avoid local sampling bias To examine the influence of water temperature and sex on asymptotic fork length estimated from the previous studies and the present study, a generalized linear mixed model (GLMM) assuming a gamma distribution and a log-link function were used Differences in catch region were defined as a random effect, since our objective was not to test for unknown regional effects The gamma GLMM was conducted using the GLMM function in the ‘‘repeated’’ package of R As an index for water temperature, we used satellitederived sea surface temperatures [SST, 11 km resolution advanced very high resolution radiometer (AVHRR): Pathfinder V5] obtained from the Ocean Watch webpage (http://las.pfeg.noaa.gov/oceanWatch/oceanwatch.php), and lðt; sÞ ¼ FL1;s ½1 À expfÀKs ðt À t0 ÞgŠ; ð1Þ where l(t, s) represents the mean fork length at age t and for sex s FL?,s and ks represent the asymptotic fork length 123 1156 Fish Sci (2012) 78:1153–1162 we used mean SSTs obtained from 2003 to 2010 in the area where dolphinfish were caught in previous studies To test the relative importance of water temperature and sex, we compared GLMMs that included terms for SST alone, sex alone, and for both SST and sex, and used the AIC to assess the best-fit model Histological observations The fixed gonads were dehydrated and embedded in paraffin, and sections (thickness lm) were obtained and stained by Mayer’s hematoxylin and eosin method, or were dehydrated and embedded in resin (Historesin) and sections were stained with % toluidine blue and % borax The stained sections were observed under an optical microscope and the most advanced testis and oocyte stages were recorded The developmental stages of testes and ovaries were classified into five and six stages of maturity, respectively, based on the development of the most advanced testes and oocytes and their histological characteristics (Figs 2, 3) The five testis stages were as follows: The six stages of oocytes were as follows: Spermatogonial proliferation stage (Sp; Fig 2a): only spermatogonia (sg) are abundant in the seminal lobule a Early spermatogenesis stage (Es; Fig 2b): spermatogonia (sg) and spermatids (st) are organized in the seminal lobules Late spermatogenesis stage (Ls; Fig 2c): spermatogenesis proceeds in the testis Spermatids (st) of the seminal lobules increase, and spermatozoa (sz) are found in the lumina of the seminal lobules Functional maturation stage (Fm; Fig 2d): spermatozoa (sz) are abundant in the lumina of the seminal lobules and main sperm duct Spermatogonial division and further spermatogenesis proceeds in the seminal lobules Postspawning stage (Ps; Fig 2e): spermatogonia (sg) are found in the seminal lobules, although spermatozoa (sz) occur in the lumina of the seminal lobules Immature stage (Im; Fig 3a): only previtellogenic (pn) oocytes are present, including those in the perinucleolus and yolk vesicle stages Developing stage (D; Fig 3b): the most advanced oocytes are at the early yolk (ey) or mid-yolk (my) stages Vitellogenic stage (Vi; Fig 3c): the most advanced oocytes are at the late yolk (ly) stage, which marks the end of vitellogenesis b c st sz sg 80µm st sg d e sz Fig Photomicrographs of testes at different developmental stages in dolphinfish a Spermatogonia proliferation stage, b early spermatogenesis stage, c late spermatogenesis stage, d functional 123 maturation stage, and e postspawning stage sg spermatogonial, st spermatid, sz spermatozoon Fish Sci (2012) 78:1153–1162 1157 Fig Photomicrographs of ovaries at different developmental stages in dolphinfish a Immature stage, b developing stage, c vitellogenic stage, d mature stage, e spawning stage, and f resting stage at atretic oocyte, ey early yolk oocyte, hy hydration oocyte, ly late yolk oocyte, my mid-yolk oocyte, pn perinucleolus oocyte, pof postovulatory follicle curve for dolphinfish A total of 141 otoliths from smallsized dolphinfish were examined Sex could not be determined for the juvenile dolphinfish whose sagittae were examined (mean FL = 25.5 mm, range 9.5–237.0 mm); however, these dolphinfish were still used in the von Bertalanffy analysis Minimum and maximum daily ages were and 53 days, respectively Scales were collected from 136 large-sized dolphinfish, and the rate of agreement between readers of the number of annual ring marks was 64.2 % (88 of the 137 specimens in total) A total of 69 scales were classified as age or older, and the remaining scales (n = 19) were estimated to be age The estimated maximum ages for males and females were five years old MIs from [age dolphinfish (n = 69) were greatest in October, November, and December, dropped in January, and stayed low during the winter months and the spawning season (see subsequent results) (Fig 4) There was a significant difference in marginal increment width per month (gamma GLM, p \ 0.05) The von Bertalanffy growth parameters were estimated for cases 1–4 (Table 1) When we used case 1, the minimum AIC was obtained, and the DAIC value of the next most parsimonious case (case 2) was more than [22] The relationship between age and FL of the dolphinfish is shown in Fig 5a, where most of the data are within the 95 % prediction interval for both sexes (Fig 5b, c), Mature stage (M; Fig 3d): the most advanced oocytes are at the hydration (hy) stages The degenerated old postovulatory follicles (pof) appear in some ovaries at the germinal vesicle migration Spawning stage (Sp; Fig 3e): yolked oocytes and new pof are present Most pofs disappear from the ovaries before the developing oocytes attain the germinal vesicle migration stage Resting stage (Re; Fig 3f): all yolked oocytes are degenerating (atretic stage, at) and non-yolked oocytes are present Results Growth A total of 278 specimens including small dolphinfish (total length, TL 9.5–237.0 mm, n = 141) and large dolphinfish (FL 412–1124 mm, n = 137) were used for age determination Unfortunately, we could not collect the fish between 237 and 412 mm because this size range of dolphinfish does not support economically important commercial fisheries in this study area However, we obtained a sufficient wide size range to describe the general growth 123 1158 Fish Sci (2012) 78:1153–1162 3.2 2.4 MI 1.6 11 0.8 15 Fork length (mm) 1200 900 600 Male Female Small Male mean Male 95 % PI Female mean Female 95 % PI 300 0 Dec Nov Oct Sep Aug Jul Jun May Apr Mar Feb Jan 0 Month Age Fig Box plot of the marginal increment width (mm) for dolphinfish (sampled from May 2008 through May 2010) pooled by month (January–December) Sample sizes are given above the box for each month Fig Relationship between age and fork length for male (black) and female (gray) dolphinfish The mean growth curves and 95 % prediction intervals are indicated by solid lines and dotted lines, respectively Table Estimated parameters and comparison of AIC scores for the four von Bertalanffy growth curve cases Sex Parameter AIC DAIC FL?,s ks t0 1048.7 0.84 -4.7 10-14 -3007.0 937.6 1.03 1010.7 0.93 -2.5 10-12 -3018.6 11.5 995.8 0.92 -4.2 10-10 -3019.7 1.1 994.4 0.90 -5.2 10-11 -3020.9 1.2 Case Male Female Case Male Female 979.0 Case Male Female Case Male Female 0.94 supporting the model for case The von Bertalanffy growth curves are thus shown separately for males and females The mean growth curve of dolphinfish was estimated in males and females as follows: 19.7 to 27.4 °C There was a significant positive relationship between FL1 and SST (p \ 0.05) The best-fit model was FL1 ¼ expð5:87 þ 0:053  SSTÞ: Â È Éà lðt; maleÞ ¼ 1049 À exp À0:835ðt þ 6:975  10À14 Þ lðt; femaleÞ ¼ 938½1 À expfÀ1:029ðt þ 6:975  10À14 ÞgŠ: Annual reproductive cycle Comparison of the AIC scores (Table 2) revealed that the model that included a term for SST but not sex provided the best explanation of the variation in asymptotic fork length The relationship between the asymptotic fork length and SST was plotted (Fig 6), and SST ranged from A total of 329 large dolphinfish (FL 412–1124 mm, 112 male and 217 female) were used for reproductive characterization (137 of 329 specimens were used for the aging study) Length-adjusted mean gonad weights varied significantly with month (gamma GLM, p \ 0.001) for both male and female dolphinfish (Fig 7) The mean value of 123 Fish Sci (2012) 78:1153–1162 1159 Table Comparison of the AIC scores for alternative models to explain variation in asymptotic fork length in terms of sea surface temperatures (SST), sex, and their interaction The cases are listed from best to worst based on AIC and DAIC 131.9 1.8 137.9 6.0 Sex 139.2 1.3 35 25 Jan SST, sex, SST sex Null model 0.6 Dec 0.1 Nov 130.1 Oct SST, sex Sep 1.3 Jul 130.0 1.2 Aug SST sex 12 Jun May 128.7 Apr SST Mar DAIC 1.8 Feb AIC a Male GSI Fixed effect 2.4 Month 1800 Florida 20 North Carolina 1400 1200 41 28 10 11 Feb Jan 1000 42 Mediterranean 800 15 Female GSI 29 26 15 20 Dec Nov Oct Sep Aug Jul Jun May Present study Apr Male Female Mar Asymptotic fork length (mm) b Puerto Rico 1600 Month 22 24 26 28 SST (ºC) Fig Relationship between SST and asymptotic fork length, as reviewed by Oxenford [11] The models are indicated by solid lines, the gray and light gray zones indicate the 50 and 95 % prediction intervals, respectively GSI in male dolphinfish was high (GSI [0.7) from May to August (Fig 7a), and in female dolphinfish (GSI [4.5) from June to August (Fig 7b) The maximum values of the mean GSI for males and females were 1.9 in May and 16.4 in July, respectively The mean GSI value became low in September, and was below 0.4 in males and 1.5 in females from September to March Immature males (Sp, Ls, and Es stages) of the dolphinfish were observed from October to May (Fig 8a) Males with testes at the Fm stages appeared in June (100 %) and July (54.5 %), although it is important to note that only one and two specimens were collected, respectively Immature females (Im and D stages) of dolphinfish were observed from September to June (Fig 8b) Females with ovaries at the Vi stage appeared from June (12.1 %) and August (12.5 %) Specimens collected in June to August had ovaries at the Vi or M stages, and females with ovaries at the Sp stage were also observed Fig Box plots of gonadosomatic index (GSI) for a male and b female dolphinfish (sampled from May 2008 through May 2010) pooled by month (January–December) Sample sizes are given above the box for each month The proportion of Sp-stage females was highest in July Females with ovaries at the Re stage were found from August and October Spawning size and GSI Sexually mature males were defined as individuals with testes at the Fm stage Sexually mature females were defined as individuals with ovaries with Vi, M, or Sp stage oocytes GSI values for immature stages (Sp to Ls) and the mature stage (Fm) overlapped, and these stages ranged from 0.5 to 0.9 (Fig 9a) Individuals with testes at the Fm stage were also larger than 524 mm FL (Fig 9b) GSI values of female individuals were less than 0.8 in the immature (Im) stage, and the values for the oocytes ranged from 0.2 to 4.0 in the developing (D) stage (Fig 9c) GSI values for females in the Vi, M, and Sp stages ranged from 3.3 to 11.5 The minimum fork length of females in the mature (from Vi to Sp) stages was 514 mm FL (Fig 9d) 123 1160 a Fish Sci (2012) 78:1153–1162 n= 2 11 39 100 Ps Fm Ls Es Sp Frequency (%) 80 60 40 Dec Oct Nov Sep Jul Aug Jun May Apr Feb Mar Jan 20 Month b n= 100 11 33 15 44 Re Sp M Vi D Im Frequency (%) 80 60 40 20 Dec Oct Nov Sep Aug Jul Jun May Apr Mar Feb Jan Month Fig Monthly variations in the frequency of occurrence of various maturation stages of a testes and b ovaries in dolphinfish For males: Sp spermatogonial proliferation stage, Es early spermatogenesis stage, Ls late spermatogenesis stage, Fm functional maturation stage, Ps postspawning stage For females: Im immature stage, D developing stage, Vi vitellogenic stage, M mature stage, Sp spawning stage, Re resting stage Discussion Age and growth This study is the first to use sagittal otoliths and scales to determine daily and annual ages of dolphinfish from the northern East China Sea The von Bertalanffy growth parameters were elucidated and the FL1 values of male and female dolphinfish were estimated to be 1049 and 938 mm, respectively, while the k values in males and females were 0.835 and 1.029, respectively The growth parameters of dolphinfish in the southwestern Sea of Japan adjacent to the northern East China Sea were analyzed using length frequency [4] According to that study, the FL? and k values were 1750 and 0.22 mm, respectively, which were pooled in males and females The initial growth rate of the dolphinfish examined here was faster than that of those from the southwestern Sea of Japan, but 123 the maximum sizes of both sexes in this study were smaller than those from the southwestern Sea of Japan Kojima [4] did not have small fish in his sample This study is the first to use sagittal otoliths to determine daily ages of dolphinfish near the East China Sea Therefore, we suggest that the growth parameters estimated in this study are more useful for examining and comparing growth among other regions The asymptotic fork length of dolphinfish in the northern East China Sea shows a greater similarity to the asymptotic fork length of western Mediterranean Sea dolphinfish [12] than to the asymptotic fork lengths of dolphinfish in other regions (Fig 6) However, to the best of our knowledge, the first-year growth for dolphinfish from the northern East China Sea is the smallest in the world It is well known that differences in estimated growth between regions [5, 6] can be related to environmental conditions (i.e., water temperature, food availability, exploitation levels) Moreover, temperature appears to be the most important environmental factor affecting growth in fish Because of the importance of temperature as a controlling factor [23], the physiological literature is replete with examples of studies evaluating thermal effects on fish [24– 26] Although differences in the growth of dolphinfish among regions have been found [10, 11], few measurements of the effect of temperature on the growth of dolphinfish have been performed Our study is unique in that it shows that there were clear distinctions in asymptotic fork length with respect to water temperature (Fig 6) However, additional bioenergetic data are required to parameterize models that attempt to depict patterns of growth observed in dolphinfish Of particular importance are data describing the effects of water temperature, body size, and feeding on metabolism The asymptotic fork length of dolphinfish was significantly larger in males than in females in this study, which reflects results from Florida and North Carolina (Fig 6) However, the asymptotic fork length of dolphinfish was larger in females than in males from the Mediterranean and Puerto Rico (Fig 6) Differences in growth features due to different laboratory methods can not be excluded For example, age determination of dolphinfish based solely on otoliths was found to underestimate the ages of older, larger fish [12] Obviously, one of the main ways to identify the factors responsible for this inter-region variability in growth would be to standardize age and growth methods Reproduction There are no reports regarding dolphinfish maturation in the East China Sea that utilized histological techniques Kojima [4] estimated the spawning period by examining Fm Ls Es Sp a 0.4 0.7 Testis maturation stage Ps Ps Fm Ls Es Sp 1.4 b 400 Re Sp M Vi D Im c GSI seasonal changes in oocyte diameter obtained from dolphinfish in the southwestern Sea of Japan, which is adjacent to the northern East China Sea We used histological techniques and examined the relationship between the most advanced oocyte stage and GSI values Previous studies of the reproductive characteristics of dolphinfish revealed that dolphinfish spawned throughout the year, with reproductive activity peaking in February to March in the southern East China Sea on the east coast of Taiwan [16] On the other hand, in the northern East China Sea, the GSI values in both sexes were high, and oocytes at the spawning stage in dolphinfish occurred from June to August in our study These results suggest that peak spawning in dolphinfish in the northern East China Sea occurs from June to August However, it is not clear whether these differences in spawning season in the East China Sea occur due to geographic differences in dolphinfish distribution (i.e., respective latitudes and physical conditions) or genetic differences among the dolphinfish In the future, controlled experiments to examine how environmental conditions affect the reproduction of dolphinfish and to detect the genetic population structure [28, 29] are needed to clarify any differences in growth and reproduction among different areas Generally, FL at 50 % maturity (L50) was used as the index of size at maturity for dolphinfish by fitting a logistic function to the frequency of mature fish for each body size class [10, 16, 27] The L50 determined in the Mexican 600 800 1000 1200 Fork length (cm) 10 12 Oocyte maturation stage GSI Oocyte maturation stage Fig Relationships between a the five maturation stages of testes and gonadosomatic index (GSI), b the five maturation stages of testes and fork length, c the six maturation stages of ovaries and GSI, and d the six maturation stages of ovaries and fork length of dolphinfish Refer to Figs and for each testis and ovarian stage, respectively Crosses in c and d indicate that postovulatory follicles were observed 1161 Testis maturation stage Fish Sci (2012) 78:1153–1162 Re Sp M Vi D Im d 400 600 800 1000 Fork length (cm) Pacific (L50 = 483.8 and 505.7 mm for females and males, respectively) [17], Taiwanese waters (L50 = 510 mm for both sexes) [16], and off the coast of North Carolina (L50 = 458 and 476 mm for females and males, respectively) [10] agree with values for fish that are less than one year old, regardless of sex We were unable to estimate L50 for dolphinfish in both sexes from the East China Sea because of a lack of reproductive characterization of smallsized individuals during the spawning season Nevertheless, we determined that the smallest individuals with matured testis and oocytes were 524 and 514 mm, respectively, with an estimated age of less than one year in both sexes Hence, dolphinfish reach sexual maturity in their first year of life in the East China Sea, which is similar to other regions [10, 16, 27] Clearly, it is necessary to monitor variations in reproductive characteristics in future studies, and to further determine the growth and maturity processes of fish that are yet to reach one year of age, in order to elucidate size at sexual maturation in the northern East China Sea Acknowledgments We thank Dr H Tanaka at the Seikai National Fisheries Research Institute for his cooperation during the study, Mr E Kusaba, D Tawara, Y Mori and other members of the Takahama Fisherman’s Association, and H Tsubakiyama of Wakamatsu Fisherman’s Association for collecting the samples We also thank Dr G.N Nishihara, who assisted with the interpretation and the English of the manuscript This study was supported by the Fisheries Research Agency 123 Fish Sci (2012) 78:1321–1329 residues on PTP1B (Fig 4) Moreover, the binding energies of both compounds were negative (-7.66 kcal/mol for fucoxanthin and -10.18 kcal/mol for compound 23), indicating that additional hydrogen bonding might stabilize the open form of the enzyme and potentiate tighter binding to the active site of PTP1B, resulting in more effective PTP1B inhibitors Discussion Hyperglycemia and diabetes may play important roles in the pathogenesis of diabetic complications through several mechanisms, including increased AR-related polyol pathway flux, increased AGE formation, overexpression of AGE receptors, activation of protein kinase C isoforms, increased hexosamine pathway flux, and excessive oxidative stress, such as superoxide overproduction, glycoxidation, glucose autoxidation, and protein glycation [7] Among several proposed mechanisms, the inhibition of AGE formation and RLAR and HRAR activity has been considered when evaluating the antidiabetic complications of fucoxanthin AR is an NADPH-dependent oxidoreductase, one of the most important enzymes in the polyol pathway In the hyperglycemic state, a surge in the rate of the AR-related polyol pathway augments the reduction of various sugars to sugar alcohols, such as glucose to sorbitol, followed by NADH-dependent sorbitol dehydrogenase catalyzed fructose production Increased fructose formation leads to reactive dicarbonyl species, which are key to AGE formation [29, 30] In addition, the sorbitol and its metabolites accumulate in nerves, retina, lens, and kidney due to their poor penetration across membranes and inefficient metabolism, resulting in the development of diabetic complications [31] As a part of our continuous search for therapeutic agents for diabetes and diabetic complications from natural marine sources, we investigated the inhibitory activities of fucoxanthin isolated from E bicyclis and U pinnatifida against HRAR, RLAR, AGE, PTP 1B, and a-glucosidase In the present study, we found that fucoxanthin inhibited both HRAR and RLAR activity along with AGE formation Further enzyme kinetic study in the presence of varying substrate and inhibitor concentrations revealed that fucoxanthin competitively inhibits RLAR, indicating that fucoxanthin can bind to the active site of the RLAR enzyme in order to prevent enzyme–substrate complex formation Considering that AGE inhibition was more effective than AR inhibition, fucoxanthin might mediate its inhibition of diabetic complications through the inhibition of AGE formation rather than through the AR-related polyol pathway Mammalian a-glucosidase, which is located in the brush-border surface membrane of intestinal cells, is a key 1327 enzyme that catalyzes the final step in the digestive process of carbohydrates [9] In contrast, PTP1B is localized on the cytoplasmic surface of the endoplasmic reticulum in classical insulin-targeted tissues such as the liver, muscle, and fat [32] This enzyme is a negative regulator of insulin signaling and plays a key role in the development of insulin resistance, which has been implicated in metabolic syndrome [33] The former therefore suppresses the influx of glucose from the intestinal tract to vessels, while the latter increases the glucose uptake from vessels into cells, leading to a decrease in postprandial hyperglycemia that can alleviate diabetes and its complications An effective therapeutic approach to treating type II diabetes is therefore to inhibit PTP1B and a-glucosidase, with a subsequently enhanced insulin action and reduced plasma glucose level to regulate glucose homeostasis Since the modulation of postprandial hyperglycemia may play a crucial role in the treatment and prevention of diabetes and its complications, a-glucosidase inhibitors and PTP1B inhibitors were selected as therapeutic approaches [8, 9] Structure-based enzyme mechanism studies have been prominently used to elucidate the mechanism of inhibition With respect to structural information on enzymes and inhibitors, various 3D-molecular docking programs have been developed in recent years However, limitations have been imposed on the explanation for the enzyme–inhibitor complex, including the binding affinities of enzyme inhibitors and enzyme substrates, as well as the reaction velocity Therefore, kinetic studies will take advantage of supporting evidence for the predicted mechanism gained from molecular docking models Since the crucial enzymes for diabetic complications and diabetes are RLAR and PTP1B, and fucoxanthin inhibits both of these enzymes, we performed enzyme kinetic analysis using Lineweaver–Burk and Dixon plots [26–28] In the present study, fucoxanthin was found to be a potent PTP1B inhibitor Further, a PTP1B kinetic study revealed that fucoxanthin was a mixed-type inhibitor, indicating that fucoxanthin can bind to the allosteric site of the free enzyme or to the enzyme–substrate complex In spite of the marked PTP1B-inhibitory activity, fucoxanthin showed weak a-glucosidase inhibition The higher selectivity toward PTP1B as an inhibitor compared to that of a-glucosidase suggests that fucoxanthin might be a strong candidate for the treatment of type II diabetes through the suppression of a negative regulator of insulin signal transduction In order to confirm the inhibition mode of the PTP1B enzyme, we predicted the 3D structure of PTP1B using Autodock 4.0 to simulate the binding of fucoxanthin and compound 23, a well-scrutinized PTP1B inhibitor of the enzyme Compound 23 is among the most potent nonpeptic PTP1B inhibitors reported to date [34] The Autodock 4.0 123 1328 docking program was used to dock the compounds into the binding sites of the crystallographic structures defined as ˚ from the inhibitor in the original all residues 5*6 A complex Currently, automated docking is widely used as an effective means of quickly and accurately predicting biomolecular conformations and binding energies of protein–ligand complexes in molecular design In particular, Autodock 4.0 uses a semiempirical free-energy force field to predict the binding free energies of protein–ligand complexes of a known structure and the binding energies for both the bound and unbound states [35] Similar to the compound 23–PTP1B complex, fucoxanthin was stably posed in the same pocket of the PTP1B through three hydrogen-bond interactions between the Phe30, Phe52, and Gly183 residues of the enzyme and the two hydroxyl groups of fucoxanthin as well as hydrophobic interactions between long hydrocarbons of fucoxanthin harboring conjugated double bonds and the Ile219, Tyr46, Val49, and Ala217 residues on PTP1B (Figs 3, 4) Moreover, the binding energy of fucoxanthin had a negative value (-7.66 kcal/mol), indicating that additional hydrogen bonding might stabilize the open form of the enzyme and potentiate tighter binding to the active site of PTP1B, resulting in more effective AR inhibition Although fucoxanthin might have been an effective PTP1B inhibitor in our molecular docking study, the bioavailability of dietary fucoxanthin is reported to be low in humans Recent studies revealed that orally administered fucoxanthin was hydrolyzed by lipase and esterase to fucoxanthinol and then absorbed in the gastrointestinal tract, followed by conversion to amarouciaxanthin A in the liver [36, 37] In spite of the biotransformation of fucoxanthin, the key functional groups and hydrophobic chains binding the PTP1B enzyme are retained Moreover, several studies have suggested that a small amount of fucoxanthin is not metabolized after long-term oral administration [38] However, fucoxanthinol and its metabolite amarouciaxanthin A are well-known major metabolites of fucoxanthin, so further molecular docking simulations of these two metabolites should be performed in order to clarify their beneficial effects In conclusion, fucoxanthin exhibited promising antidiabetic and antidiabetic complication potential by inhibiting HRAR, RLAR, and AGE formation The results of the present study demonstrate that fucoxanthin may primarily improve insulin signaling by enhancing the level of insulinstimulated receptor activation, possibly due to its strong inhibitory effect on PTP1B This effect of fucoxanthin might be useful for attenuating insulin resistance in type diabetic and obese patients Further, it strongly inhibited AGE formation and moderately inhibited HRAR and RLAR, suggesting that it has promising potential to alleviate hyperglycemia-associated complications in diabetes 123 Fish Sci (2012) 78:1321–1329 Considering the importance and severity of diabetes and diabetic complications, any new therapeutic innovation is of interest to prevent the deleterious effects of hyperglycemia In the present study, fucoxanthin showed promising inhibitory potential against PTP1B, AR, and AGE formation, and thus holds promise for its use as a therapeutic agent for the treatment of diabetes as well as related complications Acknowledgments This work was 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in mice and HepG2 cells: formation and cytotoxicity of fucoxanthin metabolites Drug Metab Dispos 32:205–211 38 Peng J, Yuan JP, Wu CF, Wang JH (2011) Fucoxanthin, a marine carotenoid present in brown seaweeds and diatoms: metabolism and bioactivities relevant to human health Mar Drugs 9:1806–1828 123 Fish Sci (2012) 78:1331–1336 DOI 10.1007/s12562-012-0561-x ORIGINAL ARTICLE Food Science and Technology Comparative studies on lipid profiles and amino acid composition of wild and cultured Dojo loach Misgurnus anguillicaudatus obtained from southern Japan Jian Gao • Shunsuke Koshio • Binh Thanh Nguyen Weimin Wang • Xiaojuan Cao • Received: April 2012 / Accepted: 18 September 2012 / Published online: October 2012 Ó The Japanese Society of Fisheries Science 2012 Abstract The aim of this study was to determine the differences in the nutritional properties of wild and cultured loach Misgurnus anguillicaudatus obtained from southern Japan Major parameters, such as whole-body proximate composition, lipid classes, and fatty acid and amino acid composition, were investigated The whole-body total lipid content of cultured loach was twofold higher than that of wild loach and the proportion of neutral lipids was significantly higher in cultured loach than in wild loach However, the polar lipid content was two- to threefold lower in cultured loach than in wild loach Compared to the wild loach, higher contents of 20:5n-3 and 22:6n-3 were detected in cultured loach, but much lower contents of 20:4n-6 In terms of wholebody amino acid composition, wild and cultured loach showed similar profiles In conclusion, the consumption of cultured loach will contribute to dietary n-3 highly unsaturated fatty acids intake, with a benefit to human health Keywords Dojo loach Á Misgurnus anguillicaudatus Á Wild and cultured fish Á Fatty acid composition Á Amino acid composition Á Lipid class Introduction Dojo loach or weatherfish Misgurnus anguillicaudatus is one of the most important cultured freshwater fish in J Gao Á S Koshio Á B T Nguyen Laboratory of Aquatic Animal Nutrition, Faculty of Fisheries, Kagoshima University, Kagoshima 890-0056, Japan W Wang Á X Cao (&) College of Fisheries, Key Lab of Freshwater Animal Breeding, Ministry of Agriculture, Huazhong Agricultural University, Wuhan 430070, Hubei, People’s Republic of China e-mail: crescent1985@yahoo.cn; caoxiaojuan@mail.hzau.edu.cn several East Asian countries, including China, Korea, and Japan In recent years, market demand for this species has increased as a result of increased human consumption as well as its use in traditional Chinese medicine [1] However, the supply of wild loach has been declining due to the effects of pollution A number of studies have focused on investigating the breeding and reproduction [2–4], blood parameters [5], genetics and evolution [6, 7] and hybridization [8] of this species Most of the cultured loach is produced in China, Korea, and Japan To achieve a favorable supply–demand balance, several artificial fish culture techniques have been used for farming loach in these countries Recently, a high stocking density tank culture technique for loach has been successfully developed in southern Japan, which contributes greatly to the development of the loach aquaculture industry It is well known that culture at high stocking densities affects some aspects of cultured fish, such as alterations in blood parameters [9], the lipid profile [10], and nutritional value However, there have been no published studies comparing the nutritional parameters of wild and cultured loach In the study reported here, we compared whole-body proximate composition, lipid classes, fatty acids, and amino acids between the wild and high-density cultured loach Misgurnus anguillicaudatus with the aim of obtaining nutritional information essential to improving loach aquaculture Materials and methods Experimental fish Sixty fish (mean body length 9.7 ± 0.9 cm) were used in this study Of these, 30 were wild fish (body weight 123 1332 Fish Sci (2012) 78:1331–1336 4.5 ± 1.1 g, body length 9.2 ± 0.3 cm), collected from the river in Tamano City, Okayama Prefecture, Japan in January, and 30 were high-density cultured fish (body weight 10.6 ± 1.5 g, body length 10.2 ± 0.9 cm), obtained from Yoshino Fish Hatchery, Oita Prefecture, Japan The cultured fish, reared in a concrete tank under high-density conditions (about 15 kg/m2), were fed with a commercial feed (Nosan Corp, Yokohama, Japan) All fish were acclimated in a circulation water system tank without feeding for days prior to analysis The body weight and fork length of all fish in each group were measured for condition factor (CF) Ten fish from each group were randomly collected and stored at -80 °C for whole-body analysis The other 20 fish were pooled together, stored in a plastic bag, and freeze-dried for the analysis of lipid and amino compositions amount of norleucine as an internal standard and hydrolyzed with N methanesulfonic acid at 110 °C for 22 h The pH of the hydrolysate was adjusted to 2.2, then filtered and stored at °C The chromatographic separation and analysis of the amino acids were performed with the HPLC unit with an ion exchange resin column Proximate analysis Results Proximate compositions of the diet and body samples were analyzed in triplicate for protein, lipid, ash, and moisture content Protein content was determined by the microKjeldahl method (Tecator Kjeltec System, 1007 Digestion System, 1002 Distilling Unit and Titration Unit; Foss Tecator, Ho¨gana¨s, Sweden) Total lipid content was measured by the Bligh and Dyer method [11], and ash and moisture contents were analyzed according to the methods of the American Organization of Analytical Chemistry [12] The proximate composition and fatty acid composition of the diet are shown in Table The whole-body proximate composition analyses of wild and cultured loach are presented in Table Wild loach contained significantly higher levels of moisture and crude ash than cultured loach In contrast, total lipid content, crude protein, and the CF were significantly lower in wild loach than in cultured loach The lipid class compositions of wild and cultured loach are listed in Table The NL proportion was significantly higher in cultured loach than in wild loach, whereas the proportion of PL was significantly lower in cultured loach than in wild loach The major NL in cultured loach was triglyceride (TG), while phosphatidylinositol (PI) and phosphatidylcholine (PC) were the major phospholipids in wild loach The whole-body fatty acid compositions of wild and cultured loach are shown in Table The cultured loach had significantly higher percentages of 20:5n-3 (eicosapentaenoic acid, EPA), 22:6n-3 (docosahexaenoic acid, DHA), 22:5n-3, and total –3 fatty acids than the wild loach On the contrary, the percentages of 18:2n-6 and 20:4n-6 were significantly lower in cultured loach than in wild loach The whole body TAA compositions of wide and cultured loach are shown in Table The levels of lysine, arginine, and tryptophan were significantly higher in wild loach than in cultured loach, while no differences were found for other amino acid contents between wild and cultured loach Lipid analysis Total lipids were extracted from the whole body according to the method of Bligh and Dyer [19] and further separated into neutral (NL) and polar lipid (PL) fractions by column chromatography (Sep-Pak Silica Cartridges; Waters Corp Milford, MA) according to Juaneda and Rocquelin [13] The lipid classes were determined in the NL and PL fractions by thin layer chromatography equipped with a flame ionization detector (TLC/FID) using Iatroscan MK-6s in combination with a computing integrator, Iatrocorder TC21 (Iatron Laboratories, Tokyo, Japan) according to Floreto et al [14] The fatty acid composition of the total lipid fractions of the diet and whole body was determined using a gas chromatography (GC-17A; Shimadzu Corp, Kyoto, Japan; column: OmegawaxTM320) according to the method of Teshima et al [15] Statistical analysis Data obtained from the biochemical analysis were subjected to one-way analysis of variance (ANOVA), and significant differences among treatments (P \ 0.05) were evaluated by Tukey–Kramer test using package SuperANOVA (Abacus Concepts, Berkeley, CA) The results were presented as mean ± standard error (SE) Total amino acid analysis Total amino acid (TAA) concentration in the whole body was analyzed using high-performance liquid chromatography (HPLC; Shimadzu Corp.) according to Teshima et al [16] In brief, 2-mg samples were spiked with a known 123 Discussion The results of our study show that wild loach contained significantly higher levels of moisture and crude ash than Fish Sci (2012) 78:1331–1336 1333 Table Proximate composition and fatty acid composition of diet Proximate composition/fatty acid composition % Table Whole-body lipid class composition of wild and cultured loach Lipid class Wild Cultured p value RNeutral lipid 75.1 ± 0.8 a 90.7 ± 0.5 b \0.001 RPolar lipid 24.9 ± 0.8 b Proximate composition Moisture (wet matter) 8.6 Lipid (dry matter) 6.2 Ash (dry matter) 15.8 Protein (dry matter) 46.4 Fatty acid composition 14:0 5.9 16:0 14.5 17:0 4.9 Monoglycerides 4.0 ± 1.0 9.3 ± 0.5 a \0.001 2.8 ± 0.6 [0.05 7.8 ± 2.1 4.9 ± 1.0 [0.05 Triglycerides 59.2 ± 2.4 a 79.6 ± 0.5 b \0.001 Sterol esters 0.4 ± 0.2 0.3 ± 0.1 [0.05 Cholesterol Free fatty acids 3.3 ± 0.2 b 0.4 ± 0.2 a 0.6 ± 0.1 a 2.5 ± 0.6 b \0.001 0.004 Dioleylglutamide 25.3 Phosphatidylethanolamine 1.1 ± 0.2 b 0.3 ± 0.1 a 0.003 16:1n-7 18:1n-9 8.1 18.6 Phosphatidylinositol 6.4 ± 0.3 b 1.5 ± 0.1 a \0.001 Phosphatidylserine 0.5 ± 0.1 0.3 ± 0.3 [0.05 18:1n-7 5.7 Phosphatidylcholine 13.1 ± 0.2 b 6.1 ± 0.7 a \0.001 20:1n-11 4.2 Lysophosphatidylcholine 1.1 ± 0.2 b 0.3 ± 0.2 a 0.010 2.5 ± 0.4 b 0.8 ± 0.3 a 0.003 RSFA 1.0 Sphingomyelin 22:n-11 3.3 RMUFA 40.9 18:2n-6 19.1 20:2n-6 0.4 Values [mean ± SEM (n = 3)] are given as the percentage lipid composition Means in each row followed by different lowercase letters are significantly different at p \ 0.05 Absence of letters indicates no significant difference between treatments 20:1n-9 20:4n-6 2.0 Rn-6 HUFA 21.5 Table Whole-body fatty acid composition of wild and cultured loach 18:3n-3 1.1 18:4n-3 1.3 20:5n-3 4.6 14:0 2.0 ± 0.1 a 3.9 ± 0.1 b \0.001 22:5n-3 1.6 15:0 1.8 ± 0.1 b 0.8 ± 0.0 a \0.001 3.7 16:0 17:0 16.4 ± 0.1 a 5.0 ± 0.1 b 20.0 ± 0.3 b 1.9 ± 0.2 a \0.001 \0.001 Values are mean values of three samples and are presented as the percentage of total fatty acids RSFA 25.3 ± 0.3 a 26.6 ± 0.3 b 0.005 16:1n-7 9.6 ± 0.0 a 10.1 ± 0.2 b 0.025 SFA Saturated fatty acid, MUFA mono-unsaturated fatty acid, n-6 HUFA –6 highly unsaturated fatty acid, n-3 HUFA –3 highly unsaturated fatty acid 18:1n-9 5.7 ± 0.2 b 3.7 ± 0.2 a \0.001 18:1n-7 17.6 ± 0.1 a 18.6 ± 0.3 b 0.007 20:1n-9 1.9 ± 0.1 a 4.0 ± 0.0 b \0.001 22:6n-3 Rn-3 HUFA 12.3 Table Whole-body proximate compositions of wild and cultured loach Whole-body proximate composition Wild Cultured p value Fatty acids \0.001 Cultured p value 22:1n-11 0.4 ± 0.1 a 1.6 ± 0.0 b \0.001 RMUFA 35.2 ± 0.2 a 37.9 ± 0.4 b \0.001 18:2n-6 12.5 ± 0.2 b 10.8 ± 0.1 a \0.001 20:2n-6 0.3 ± 0.1 0.2 ± 0.0 [0.05 20:4n-6 5.1 ± 0.1 b 0.8 ± 0.0 a \0.001 17.9 ± 0.3 b 11.7 ± 0.1 a \0.001 4.0 ± 0.0 b 1.1 ± 0.0 a \0.001 Rn-6 HUFA Total lipid Wild 2.8 ± 0.0 a 7.7 ± 0.2 b Moisture 74.3 ± 0.4 b 69.7 ± 1.4 a 0.005 18:4n-3 0.6 ± 0.0 a 0.9 ± 0.0 b \0.001 Crude ash 3.2 ± 0.1 b 2.8 ± 0.1 a 0.01 16.3 ± 0.3 a 18.3 ± 0.2 b \0.001 20:4n-3 20:5n-3 0.4 ± 0.0 3.8 ± 0.1 a 0.4 ± 0.0 5.4 ± 0.0 b [0.05 \0.001 0.5 ± 0.1 a 1.0 ± 0.1 b \0.001 Crude protein CF (%) All values are given as the percentage wet matter and expressed as the mean of three samples ± the standard error of the mean (SEM), except for CF, which is expressed as the mean ± SE ( (n = 30) Means in each row followed by a different lowercase letter are significantly different at p \ 0.05 CF Condition factor 18:3n-3 22:5n-3 1.9 ± 0.3 1.9 ± 0.0 [0.05 22:6n-3 6.7 ± 0.1 a 10.9 ± 0.0 b \0.001 17.5 ± 0.4 a 20.6 ± 0.0 b \0.001 Rn-3 HUFA Values [mean ± SEM (n = 3)] are given as the percentage (%) total fatty acid methyl esters Means in each row followed by different lowercase letters are significantly different at p \ 0.05 Absence of letters indicates no significant difference between treatments 123 1334 Fish Sci (2012) 78:1331–1336 Table Total amino acid (g/100 g dry) of whole body of wild and cultured loach Amino acids Wild Cultured p value EAA Arginine 2.85 ± 0.12 b 2.22 ± 0.25 a Histidine 1.80 ± 0.11 1.73 ± 0.12 [0.05 Isoleucine 1.80 ± 0.08 1.59 ± 0.21 [0.05 Leucine 4.20 ± 0.14 3.76 ± 0.30 [0.05 Lysine 6.29 ± 0.08 b 5.30 ± 0.32 a Methionine Phenylalanine 2.12 ± 0.09 2.43 ± 0.09 1.90 ± 0.41 2.24 ± 0.16 [0.05 [0.05 Threonine 2.48 ± 0.10 2.21 ± 0.18 [0.05 Valine 1.23 ± 0.15 1.16 ± 0.06 [0.05 Tryptophan 1.26 ± 0.10 b 0.90 ± 0.06 a 0.005 30.01 ± 0.79 b 26.11 ± 1.75 a 0.025 REAA 0.017 0.007 NEAA Taurine 0.29 ± 0.02 0.36 ± 0.01 [0.05 Aspartic acid 5.58 ± 0.18 5.02 ± 0.28 [0.05 Glutamic acid 8.03 ± 0.37 7.29 ± 0.50 [0.05 Serine 2.59 ± 0.12 2.42 ± 0.13 [0.05 Proline 2.40 ± 0.05 2.32 ± 0.10 [0.05 Glycine 2.63 ± 0.08 2.86 ± 0.18 [0.05 Alanine 3.37 ± 0.07 3.32 ± 0.12 [0.05 Tyrosine 2.08 ± 0.07 1.81 ± 0.17 [0.05 Cystine RNEAA 3.38 ± 0.24 30.36 ± 0.93 3.18 ± 0.37 28.59 ± 1.19 [0.05 [0.05 56.82 ± 1.48 b 51.59 ± 2.47 a RAA 0.035 Values [mean ± SEM (n = 3)] are given as grams per 100 g dry body weight Means in each row followed by different lowercase letters are significantly different at p \ 0.05 Absence of letters indicates no significant difference between treatments EAA Essential amino acid, NEAA non-essential amino acid, AA amino acid cultured loach On the other hand, the whole-body TL content and CF of wild loach were significantly lower than those of cultured loach These results are in general agreement with those of previous studies showing a higher whole-body TL content in cultured fish compared with wild fish, including ayu Plecoglossus altivelis [17], European sea bass Dicentrarchus labrax [18], gilthead sea bream Sparus aurata [19, 20], red sea bream Pagrus major [21], and Atlantic halibut Hippoglossus hippoglossus [22] This TL accumulation seems to be related to a better nutritional feed under the high-density culture condition Moreover, CF was presumed to reflect the lipid content in the body A strong positive correlation between condition factor and whole-body TL content has been reported in several studies [23, 24] We consider that our results suggest that CF could be used as a factor to discriminate between wild and cultured loach 123 The NL proportion was significantly higher in cultured loach (90.7 % of TL) than in wild loach (75.1 % of TL), whereas the proportion of PL in cultured loach (9.3 % of TL) was two- to threefold lower that in wild loach (24.9 % of TL) The whole-body TL level was twofold higher in cultured loach than in wild loach The higher lipid content was mainly due to increased NL, particularly TG (79 % of TL) Similar results have also been reported in a number of studies in other freshwater fish, including tilapia [25] and ayu [17] The higher TG level of cultured loach might be related to the enhancement effect of gluconeogenic capacity from glycerol in fish in the high-stocking density culture system [9, 26] On the other hand, we found that the proportion of PL was significantly lower in cultured loach than in wild loach PI and PC were the major phospholipids In contrast with our results, Karapanagiotidis et al [25] reported that they found no significant differences in the proportion of PL between wild and cultured tilapia; these authors considered the PL content to be stable in tilapia Arakawa et al [27] also demonstrated that PL were less affected by the environment than NL in yellowtail Seriola quinqueradiata The disparity between the results reported in these studies and our results suggest that PL in loach may be more susceptible than in other fish species The importance of PL on biological functions, such as constituents of cell membranes, has been well documented not only in fish species [28–30], but also in human health studies [31] More research efforts are required to determine the site of the PL of loach under high-density culture The whole-body fatty acid composition analyses revealed large differences between the wild and cultured loach The cultured loach had significantly higher levels of saturated fatty acid (SFA), mono-unsaturated fatty acid (MUFA), and –3 highly unsaturated fatty acid (HUFA), and significantly lower –6 fatty acid contents The higher levels of SFA and MUFA in cultured loach were due to increased levels of fatty acids, such as 14:0 and 16:0, and 20:1n-9 and 22:1n-11, respectively As a general rule, the major difference in fatty acid composition between wild and cultured fish is that cultured fish contain high levels of 18:2n-6 [17–19, 32], primarily since artificial feeds for cultured fish, especially freshwater species, usually contain considerably high amounts of plant oils, which are rich in 18:2n-6 However, in our study, the proportion of 18:2n-6 in cultured loach (10.8 %) was significantly lower than that (12.5 %) in wild loach One possible explanations for the lower 18:2n-6 content in cultured loach is that this fatty acid is one of the principal lipid energy sources when fish experience high energy demands [9, 10], i.e., high-density stocking culture in our study It is well-known that –3 HUFA, especially EPA and DHA, play an important role in human health The amounts of –3 HUFA contained in wild fish compared to cultured Fish Sci (2012) 78:1331–1336 fish have been observed in a number of marine fish species [20, 32] However, we found that the amounts of EPA (5.4 %) and DHA (10.9 %) in cultured loach were significantly increased relative to the levels (EPA 3.8 %; DHA 6.7 %) in the wild loach Similarly, Saito and Okabe [17] reported a higher DHA content in cultured ayu compared to wild ayu Furthermore, Palacios et al [33] reported higher levels of EPA and DHA in cultured silverside fish Chirostoma estor estor In our study, the TAA composition pattern of cultured loach was similar to that of wild loach However, the total essential amino acid (EAA) levels in cultured loach were significantly lower than those in wild loach A similar reduction of total EAA levels in cultured silver pomfret Pampus argenteus has been reported by Zhao et al [34] Glutamine acid, lysine, and aspartic acid were major amino acids found in our study, accounting for [5 % of the TAA As such, our results are similar to those reported for other fish species, such as Japanese flounder Paralichthys olivaceus [35], red sea bream [36], sea bass [37], and sturgeon Acipenser spp [38] Although there were significant differences in the levels of arginine, lysine, and tryptophan between cultured and wild loach, there was only a slight reduction in the levels of these three amino acids in cultured loach It has been reported that an imbalance of EAA in fish tissues is caused by an imbalance of EAA in the respective diets [36, 39] However, our results suggest that cultured loach probably had well-balanced amino acid composition, similar with the wild loach This was likely due to the balanced amino acid pattern in the diet or to the possibility that EAA levels may be similar to the requirement levels for this species, although no information on amino acid requirements for loach are as yet available In conclusion, although detailed information on the lipid composition and amino acid profiles for this species is unavailable, the results of our study suggest that compared with wild loach, the cultured loach has well-balanced amino acid profiles and higher contents of –3 HUFA, such as EPA and DHA, which may meet consumer expectations Acknowledgments The authors would like to extend their gratitude to those who have taken the time to critically review this manuscript The authors also thank the Lab of Fish Genetics and Breeding, College of Fisheries, Huazhong Agricultural University, China for providing the fish The research was partially funded by the Management Expenses Grants of the United Graduate School of Agricultural Sciences, Kagoshima University provided to S Koshio References Kiros S, Aoki J, Park CB, Soyano K (2011) Annual changes in testicular development and plasma sex steroids in the captive male dojo loach Misgurnus anguillicaudatus Ichthyol Res 58:217–224 1335 Arai K, Matsubara K, Suzuki R (1993) Production of polyploids and viable gynogens using spontaneously occurring tetraploid loach, Misgurnus anguillicaudatus Aquaculture 117:227–235 Arias-Rodriguez L, Yasui GS, Kusuda S, Arai K (2010) Reproductive and genetic capacity of spermatozoa of inter-populational hybrid males in the loach, Misgurnus anguillicaudatus J Appl Ichthyol 26:653–658 Yasui GS, 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offshore aquaculture production system in Korea Do-Hoon Kim • Douglas Lipton • Jong-Yeol Choi Received: March 2012 / Accepted: 11 July 2012 / Published online: 25 August 2012 Ó The Japanese Society of Fisheries Science 2012 Abstract This study aimed to analyze the economic effect of the red sea bream Pagrus major offshore aquaculture production system in Korea Based on the data collected, revenue and expenses throughout the culture period were calculated, and the net present value and internal rate of return of the ten-year cash flow and cash outflow were estimated in order to determine the economic validity of red sea bream offshore aquaculture production Results showed that the red sea bream offshore aquaculture production system had high profitability based on the current production and market conditions This is because of its relatively high survival rate, relatively low feed conversion ratio, and good market price level However, sensitivity analyses of the main variables indicated that the profitability of red sea bream offshore aquaculture is highly vulnerable to production conditions and market condition changes Keywords Offshore aquaculture Á Red sea bream Á Sensitivity analysis Á Net present value Á Internal rate of return D.-H Kim (&) Technology Management Center, National Fisheries Research & Development Institute, Busan 619-705, Republic of Korea e-mail: delaware310@yahoo.com D Lipton Department of Agricultural and Resource Economics, University of Maryland, College Park, MD, USA J.-Y Choi Department of Business Administration, Pusan National University, Busan 609-735, Republic of Korea Introduction Recently, there has been an increasing desire to restructure the aquaculture industry in Korea due to environmental pollution resulting from inshore aquaculture as well as a relative lack of competitiveness compared to foreign farmed fishery products [1] Offshore aquaculture has been attracting attention as a means of restructuring aquaculture This is because of the expectation that offshore aquaculture produces less pollution than inshore aquaculture while offering more stable production factors, such as a better survival rate during a red tide or typhoon, as the cages can be anchored in deep areas offshore [2–5] Korea began its pilot offshore aquaculture scheme in the Pyo-Sun area of Jeju Island in 2005, as a joint project between a national research institute and private companies The Korean government gave the project permission to use 3.5 km of the sea at Pyo-Sun for three years (May 2005–May 2008); offshore cages (Seastation 3000TM) were introduced from the US and are currently being operated Initially, the rock bream Oplegnathus fasciatus was selected for culture, followed more recently by red sea bream and olive flounder, while bluefin tuna is currently being considered for culture Validity as a profitable business in an investment evaluation is one of the important factors to take into account when considering the expansion of offshore aquaculture Though offshore aquaculture has more positive environmental effects than inshore aquaculture, this advantage can be offset by high investment and operating costs, operational risk, and uncertainty For this reason, a business validity analysis is an extremely important tool when attempting to develop economically viable aquaculture companies There have been some previous economic analyses of offshore aquaculture, including the study by Jin et al [6] of 123 1338 New England Atlantic cod Gadus morhua, and the study by Kam et al [7] of Hawaii Pacific threadfin Polydactylus sexfilis offshore aquaculture Domestic studies include the economic analysis by Lipton and Kim of a rock bream offshore aquaculture pilot project [8], and the comparison made by Kim and Lipton [9] of offshore aquaculture and inshore aquaculture of rock bream However, the study described in the present paper attempted to analyze the economic effect of red sea bream Pagrus major, which is expected to be an important fish for the offshore aquaculture industry in the future, and is one of the main species farmed in inshore aquaculture (6,300 t in 2010) The analysis was performed based on biological data, cost of culture, and market conditions for offshore aquaculture in Jeju from December 2006 to March 2009 Materials and methods Analytical method To perform an economic analysis of the offshore aquaculture of red sea bream, we mainly employed a financial feasibility evaluation of individual aquaculture companies that is widely used in general aquaculture economic analysis [10–13] Based on the data collected data, revenue and costs throughout the culture period were calculated, and the net present value (NPV) and internal rate of return (IRR) of the ten-year cash inflow (CI) and cash outflow (CO) were estimated in order to determine the economic viability, as shown in Eqs and To calculate the NPV, it is necessary to estimate the costs of the offshore aquaculture production system and the cash flows that it will yield Then the costs and cash flows that occur in the future must be discounted back to the current period to account for risk and the time value of money The present value of the cash inflow can then be compared to the present value of the cash outflow, as shown in Eq n n X X CIt COt NPV ¼ À ; ð1Þ t ð1 þ kÞ ð1 þ kÞt t¼0 t¼0 where k refers to the discount rate If the value of the cash inflow is greater than the value of the cash outflow, the offshore aquaculture production system will generate wealth, given the assumptions made when calculating its costs and cash inflows The internal rate of return (IRR) is the discount rate that makes the net present value of the investment zero, as shown in Eq It is typically necessary to calculate the IRR by trial and error, substituting progressively higher interest rates into the NPV equation until the NPV is driven down to zero: 123 Fish Sci (2012) 78:1337–1342 n n X X COt CIt ; t ¼ ð1 þ rÞ ð1 þ rÞt t¼0 t¼0 ð2Þ where r refers to the IRR, which is the discount rate that produces the net present value of cash flow and cash outflow In order to consider culture conditions and changes in market conditions to a greater extent than in previous studies, Monte Carlo simulation was utilized to set the maximum and minimum values of the main variables and to induce a more realistic analytical result [6, 8, 14, 15] However, as this was a first attempt to analyze red sea bream offshore aquaculture and it used data derived from one culture product cycle, it was not plausible to assume that the main variables were probability variables and to apply a simulation method Accordingly, this study first analyzed a baseline model derived from the collected data, and then estimated the change in the profitability of red sea bream offshore aquaculture through a sensitivity analysis of the main variables, with production conditions and market environment changes taken into account For the sensitivity analysis, the survival rate, feed conversion ratio (FCR), average production weight, market price, feed cost, and fingerling cost were considered to be the main variables, thus taking variables accounted for in the previous studies into consideration Analytical data In red sea bream offshore aquaculture, 150,000 red sea bream fingerlings were stocked in one offshore sea cage (a 3,000 m3 biconical sea cage) in December 2006 and grown for 27 months until March 2009 As a result, the average survival rate was 90 % and the FCR was 1.23, which was higher than the average survival rate in inshore aquaculture (60–80 %) The average production weight of red sea bream after the culture period was 1.2 kg, and market price was US$8.93/kg The production cost during the aquaculture period is shown in Table The total production cost was US$921,719, of which labor costs (including full-time and part-time labor costs) took the highest share at 36.5 %, followed by feed costs at 22.1 %, fingerling costs at 14.5 %, and depreciation costs at 11 % Full-time labor costs included the cost of the divers’ feeding and managing facility, office staff, and the opportunity cost of two managers The part-time labor costs included the cost of hiring temporary laborers during the transplantation of the red sea bream, shipment, and repair As shown in Table 2, the initial investment cost for the aquaculture facility (one cage) was US$359,554, including cages, nets, and scuba equipment The cost of the cages, Fish Sci (2012) 78:1337–1342 1339 Table Operating expenses for the culture period Table Results for the baseline model Item description (units) Cost (US$/ unit) Total (US$) % of total Fingerlings (piece) 0.89 133,929 14.5 Feed (kg) 1.18 203,569 22.1 Electricity (monthly) 134 Fuel (monthly) 446.4 3,616 0.4 12,054 1.3 Repair/maintenance (monthly) 744.1 20,089 2.2 Full-time labor (month/person) 2,232 313,393 34.0 Part-time labor Supplies and others (monthly) 558.04 24,107 15,067 2.6 1.7 Insurance (monthly) 1,339.3 36,161 3.9 Depreciation (annually) 45,101 101,476 Lease rent (annually) 25,893 Total Useful life (years) Unit cost (US$) Quantity Cost (US$) 10 % 511,558 387,550 283,190 18.1 Table Results of the sensitivity analysis of survival rate -214,621 76,760 5.7 11.0 80 368,141 12.2 58,259 6.3 90 659,522 18.1 921,719 100.0 95 805,212 20.9 % of outlay Annual cost (US$) 310,921 310,921 86.5 38,865 22,741 22,741 6.3 2,843 Warehouse 3,571 3,571 1.0 714 4,464 4,464 1.2 893 10 17,857 17,857 5.0 1,786 359,554 100.0 45,101 359,554 659,522 8% 70 Total 836,880 IRR (%) 6% 60 Nursery nets Truck 4% NPV (US$) Cages Scuba gear NPV (US$) 2% Survival rate (%) Table Initial capital outlay and annual depreciation cost Item Discount rate including components (anchors, buoys, regular fish nets, harvest/stocking bin, spar, and rims), was US$310,921, representing 87 % of the total initial investment cost In terms of equipment lifespans, the cages and nets had average lifespans of eight years, while the scuba equipment lasted five years and the vehicles (trucks) lasted ten years The straight-line depreciation method was employed to determine the annual depreciation of facilities Results Baseline model results In the baseline model analysis of red sea bream offshore aquaculture, the return on sales for the duration of culture was high (an average of 34.1 %), and its long-term profitability was also good The results of the NPV and IRR calculations based upon the ten-year cash flow that yielded the various discount rates are shown in Table The IRR for red sea bream offshore aquaculture was 18.1 %, which is similar to the value of 18–20 % found for the IRR of IRR (%) – rock bream offshore aquaculture, which was calculated to have high profitability [8], and considerably higher than the IRR of 11 % found for olive flounder land-based aquaculture [16] With a discount rate of %, the NPV was also high: US$659,522 When the discount rate increased, the NPV decreased Sensitivity analysis of the survival rate The survival rate of red sea bream offshore aquaculture was 90 %, which is far higher than the corresponding rate for inshore aquaculture This higher rate was achieved despite the occurrence of various typhoons, demonstrating the stability of offshore aquaculture despite changes in the ocean environment However, unlike in the fish cultured inshore, there were no cases of viral disease offshore, and therefore the safety of those fish in the event of a viral disease outbreak could not be evaluated at the initial stage Sensitivity analysis was carried out for survival rates ranging from 60 to 95 %, considering that the average survival rate in current red sea bream inshore aquaculture is 60–80 % As shown in Table 4, profitability decreases sharply with decreasing survival rate In particular, if the survival rate drops below 70 %, the NPV and IRR become negative, indicating that no profit is made On the other hand, if the survival rate increases, profitability increases sharply When it is 95 %, the NPV becomes US$805,212 and the IRR becomes 20.9 % Sensitivity analysis of the FCR Extruded pellet feed for red sea bream was supplied for red sea bream offshore aquaculture, so the FCR was high (1.23) compared to the average FCR (2.0–2.5) of sea bream 123 1340 Fish Sci (2012) 78:1337–1342 inshore aquaculture The FCR is calculated from the mass of fish that is needed to produce kg of whole fish To achieve stable production and management in offshore aquaculture, the feed cost needs to be reduced, and more efficient feeding should be implemented by adopting an eco-friendly method Sensitivity analysis with a scope of -30 to ?30 % of the average FCR was carried out As shown in Table 5, profitability seems to increase sharply with decreasing FCR On the other hand, if the FCR increases, feed consumption increases, which increases production costs and thus reduces profitability If the FCR increases by 30 %, the NPV becomes US$414,658, decreasing by 37 % Sensitivity analysis of the average production weight With the Jeju offshore aquaculture scheme, there is a concern that it may be difficult to maintain a reasonable growth rate during bad ocean conditions in winter, as such conditions make periodic direct feeding by divers impossible, making feeding problematic Thus, there is a plan to install an automatic feeding machine or to ensure prompt feeding by divers To perform the sensitivity analysis of the average production weight, the scope of the production weight was set to -20 to ?20 % (Table 6) This scope corresponds to heavy fluctuations in production weight, and the profitability may reduce dramatically if the average production weight decreases For example, if the production weight decreases by 10 %, the NPV decreases by 40 % On the other hand, if the production weight increases, the profitability increases significantly If it increases by 10 %, the NPV increases by 40 % Accordingly, if the average production weight can be increased by constant feeding and appropriate breeding control, the profitability of red sea bream offshore aquaculture will improve a great deal Sensitivity analysis of the market price A sensitivity analysis of the market price was carried out to determine the effect of changes in the market price, in accordance with increased red sea bream offshore aquaculture in the future The scope was set to between -30 and 30 % of the current market price (US$8.93), and the change in profitability was evaluated according to the change in the market price (Table 7) As a result, the NPV changes markedly with the market price If the market price decreases, the profitability does too In particular, if the price of red sea bream per kg decreases below US$7.54, the NPV indicates a lack of profitability (a negative value) On the other hand, if the market price increases by 10 %, the NPV increases by about 65 % If the market price increases by 20 %, the NPV increases by 129 %, which demonstrates the high influence of the market price on profitability Sensitivity analysis of the feed cost and the fingerling cost We carried out a sensitivity analysis was of the feed cost (22.1 %) and the fingerling cost (14.5 %), which represent a high proportion of operational costs (Table 8) In Table Results of the sensitivity analysis of market price Market price NPV (US$) IRR (%) US$6.25 (-30 %) -615,698 – US$7.14 (-20 %) -190,625 – 234,449 Table Results of the sensitivity analysis of FCR FCR NPV (US$) IRR (%) 0.86 (-30 %) 904,386 22.8 US$8.04 (-10 %) 0.98 (-20 %) 824,971 21.3 US$8.93 659,522 18.1 1.11 (-10 %) 738,937 19.7 US$9.82 (10 %) 1,084,595 25.0 9.7 1.23 659,522 18.1 US$10.72 (20 %) 1,509,660 31.0 1.35 (10 %) 580,107 16.5 US$11.61 (30 %) 1,934,742 36.4 1.48 (20 %) 494,073 14.8 1.60 (30 %) 414,658 13.2 Table Results of the sensitivity analysis of feed cost Feed cost NPV (US$) IRR (%) US$0.83 (-30 %) 903,725 22.8 US$0.94 (-20 %) US$1.06 (-10 %) 822,324 740,923 21.3 19.7 Table Results of the sensitivity analysis of production weight Production weight (kg) NPV (US$) IRR (%) 0.96 (-20 %) 135,036 7.1 1.08 (-10 %) 397,279 12.8 US$1.18 659,522 18.1 1.20 659,522 18.1 US$1.30 (10 %) 578,121 16.5 1.32 (10 %) 921,765 23.0 US$1.41 (20 %) 496,720 14.9 1.44 (20 %) 1,184,008 27.5 US$1.53 (30 %) 415,319 13.2 123 Fish Sci (2012) 78:1337–1342 1341 Table Results of the sensitivity analysis of fingerling cost Fingerling cost NPV (US$) IRR (%) US$0.63 (-30 %) 792,126 21.2 US$0.71 (-20 %) 747,925 20.1 US$0.80 (-10 %) 703,723 19.1 US$0.89 659,522 18.1 US$0.98 (10 %) 615,321 17.1 US$1.07 (20 %) 571,119 16.1 US$1.16 (30 %) 526,918 15.1 particular, the feed cost becomes important when there are problems with the international supply chain, raw material cost increases, etc Through a sensitivity analysis of the feed cost, it was found that if the feed cost increases, the profitability of sea bream offshore aquaculture decreases If the feed cost increases by 10 % in the baseline model, the NPV becomes US$578,121, which is a 12 % decrease, and if it increases by 20 %, NPV decreases by 25 % On the other hand, if the feed cost decreases, profitability increases If the feed cost decreases by 10 %, the NPV increases by 12 %, and if it increases by 20 and 30 %, the NPV increases by 25 and 37 %, respectively In terms of the sensitivity analysis of the fingerling price (Table 9), if the fingerling cost increases, the profitability of sea bream offshore aquaculture decreases If fingerling cost increases by 10 % in the baseline model, the NPV becomes US$616,321, a 6.7 % decrease, and if it increases by 20 %, the NPV decreases by 13.4 % On the other hand, if the fingerling cost decreases, the profitability increases If the fingerling cost decreases by 10 %, the NPV increases by %, and if it decreases by 20 and 30 %, the NPV increases by 13 and 20 %, respectively Discussion An economic analysis of red sea bream offshore aquaculture showed that it has high profitability, based on current production and market conditions This is because of a relatively high survival rate, relatively low FCR, and good market price level Accordingly, it is fair to remark that the offshore aquaculture facility adapts well to ocean environmental changes, and that red sea bream production is carried out effectively by the facility However, as shown in a sensitivity analysis of the main variables, the profitability of red sea bream offshore aquaculture is highly vulnerable to production conditions and changes in market conditions In particular, fluctuations in the profitability according to market price changes were relatively high Thus, if the market price decreases due to excessive production or market competition with other farmed fish species, the profitability of red sea bream offshore aquaculture may decrease dramatically For this reason, it is highly necessary to maintain a reasonable market price by considering red sea bream inshore aquaculture and the production of other fish species In addition, when there is a decrease in the survival rate or production weight and the FCR, there is a decrease in the profitability Thus, effective feeding and production management are required, as well as more studies focusing on enhancing the survival rate and growth rate in offshore aquaculture The feed cost and fingerling cost were found to comprise a high proportion of the production cost The feed cost may increase if there is an increase in international prices of raw materials or a problem in the international supply chain However, there may be the potential to reduce the price by increasing fingerling production and through technical development This study was carried out based on data from a pilot offshore aquaculture project in the Jeju region However, the ability to generalize these results to other areas may be limited, due to the specific ocean environmental characteristics of the Jeju region Further comparative studies of the production and economic feasibility of red 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