Natural abundance of 15N and 13C in fish tissues and the use of stable isotopes as dietary protein tracers in rainbow trout and gilthead sea bream

For developing efficient diets, two sets of experiments examined whether the use and allocation of dietary protein can be traced by labelling with stable isotopes (¹⁵N and ¹³C) in two culture fish ( Oncorhynchus mykiss and Sparus aurata) . In the first experiment, natural abundance and tissue distribution of these isotopes were determined, by measuring the δ¹³C and δ¹⁵N values by isotopic ratio mass spectrometry, in fingerlings (14–17 g) adapted to diets differing in the percentage of fish meal replacement by plant protein sources. For both species, δ¹⁵N and δ¹³C were greater in tissues with higher protein and lower lipid content. Delta ¹⁵N of diets and tissues decreased as replacement increased, suggesting δ¹⁵N can be used as a marker for dietary protein origin. The ¹⁵N fractionation (δ¹⁵N fish − δ¹⁵N diet) differed between groups, and could thus be used to indicate protein catabolism. In the second experiment, fish (75–90 g) of each species ingested a diet enriched with ¹⁵N-protein (10 g kg⁻¹ diet) and ¹³C-protein (30 g kg⁻¹ diet). These proportions were suitable for determining that the delta values of tissue components were high enough above natural levels to allow protein allocation to be traced at 11 and 24 h after feeding, and revealed clear metabolic differences between species.     

Effects of lipid extraction on stable carbon and nitrogen isotope analyses of fish tissues: potential consequences for food web studies

Abstract –  We examined whether solvent-based lipid extractions, commonly used for stable isotope analysis (SIA) of biota, alters δ ¹⁵N or δ ¹³C values of fish muscle tissue or whole juvenile fish. Lipid extraction from muscle tissue led to only small (<1‰) isotope shifts in δ ¹³C and δ ¹⁵N values. By contrast, ecologically significant shifts (+3.4‰ for δ ¹³C and +2.8‰ for δ ¹⁵N) were observed for whole juvenile fish. Sample variance was not affected by lipid extraction. For tissue-specific SIA, two sample aliquots may be required: a lipid-extracted aliquot for stable carbon isotope analysis when differing lipid content among tissues is a concern, and a nonextracted aliquot for δ ¹⁵N determination. Whole organism SIA is not recommended because of the mix of tissues having different turnover times; for very small fish, we recommend that fish be eviscerated, decapitated, and skinned to minimise differences with samples of muscle tissue.     

Use of stable isotopes to distinguish farmed from wild Atlantic salmon, Salmo salar

Abstract –  Stable isotopes of carbon and nitrogen ( δ ¹³C and δ ¹⁵N) were examined in wild and aquaculture origin Atlantic salmon, Salmo salar , to evaluate their utility to identify escaped farmed fish. Samples of muscle tissue obtained from wild Conne River, Newfoundland, salmon were significantly more enriched in nitrogen ( δ ¹⁵N: mean = 12.75; SD ± 0.38‰) but depleted in lipid corrected carbon ( δ ¹³C': mean = −20.51; SD ± 0.23‰) by comparison with aquaculture specimens obtained from Bay d'Espoir, Newfoundland ( δ ¹⁵N = 10.96 ± 0.19‰;  δ ¹³C' = −19.25 ± 0.17‰) resulting in a complete separation of the two groups. Aquaculture specimens differed in δ ¹³C' from analyses of commercial salmon diet by 0.24‰, within the enrichment range associated with trophic transfers, while the δ ¹⁵N values in salmon muscle were enriched by 5.01‰. Although differences occurred in direct comparisons of white muscle and adipose tissue ( N  = 49), the average δ ¹³C' and δ ¹⁵N signatures varied in absolute amounts by only 0.5‰, supporting the use of adipose tissue as a nonlethal means to determine isotopic signatures of Atlantic salmon.     

Evaluation of shrimp polyculture system in Thailand based on stable carbon and nitrogen isotope ratios

ABSTRACT: To quantify the contribution by cocultured animals to waste assimilation in an intensive shrimp farm in Thailand, the food web structures of the macrobenthos in a reservoir pond, a shrimp culture pond and water treatment ponds were examined using the stable C and N isotope ratio technique. Seawater for aquaculture was drawn from a creek, and stored in a reservoir pond, used for farming the banana prawn Fenneropenaeus merguiensis in culture ponds, and then recycled through treatment ponds where the green mussel Perna viridis was cultured to remove organic wastes discharged from the farming. The clam worm Nereididae sp. and the mud creeper Cerithideopsilla cingulata in the culture pond had δ ¹³C values of −21.0‰ and −18.4‰, respectively, suggesting that shrimp feed (mean δ ¹³C = −20.7‰) was the main food source for these species. The δ ¹³C analysis also suggested that sediments (−23.7‰) in the reservoir pond and particulate organic matter (POM) (−24.0‰) and/or sediments (−25.0‰) in the treatment pond supplied carbon for most macrobenthic animals. However, green mussels in the treatment pond had a mean δ ¹³C value of −20.5‰, suggesting that shrimp feed was the main food source for this species.     

Ecological and genetic differentiation among the Arctic charr of Lake Aigneau, Northern Québec

Abstract –  Two modal size groups of sexually mature Arctic charr ( Salvelinus alpinus ) differing in shape and found at different depths in Lake Aigneau in the Canadian sub-Arctic are described and tested for genetic and ecological differentiation. Forms consisted of a small littoral resident, mean size 21.7 cm, and a large profundal resident, mean size 53.9 cm. Mitochondrial DNA analysis indicated that seven of eight haplotypes were diagnostic for either the littoral or profundal fish, with 66.6% of the variation being found within form groupings. Pairwise tests of microsatellite data indicated significant differences in nine of 12 loci and a significant difference between the forms across all tested loci. Molecular variation was partitioned to 84.1% within and 15.9% between forms and suggestive of either restricted interbreeding over time or different allopatric origins. Stable isotope signatures were also significantly different, with the profundal fish having higher δ¹³C and δ¹⁵N values than the littoral fish. Overlap and separation, respectively, in the range of form δ¹³C and δ¹⁵N signatures indicated that carbon was obtained from similar sources, but that forms fed at different trophic levels. Littoral fish relied on aquatic insects, predominantly chironomids. Profundal fish were largely piscivorous, including cannibalism. Predominantly empty stomachs and low per cent nitrogen muscle-tissue composition among profundal fish further indicated that the feeding activity was limited to the winter when ice-cover increases the density of available prey at depth. Results provide evidence of significant differences between the modal groups, with origins in both genetics and ecology.     

Carbon sources of Amazonian fisheries

Variation in the seasonal and spatial isotopic composition of plant C₄ (aquatic macrophytes) and C₃ (forest, C₃ aquatic macrophytes and algae), and that of fish [ Prochilodus nigricans Agassiz, Mylossoma duriventre (Cuvier), Colossoma macropomum (Cuvier), Semaprochilodus insignis (Schomburgk) and S. taeniurus Steindachner in the Amazon floodplain were analysed to test whether the fisheries deliver plant carbon to the population of Manaus in the same proportion as it is available in the floodplain. The contribution of C₄ plants was significantly lower in ¹³C during the season of high water levels and increased toward the west of the basin. Mylossoma duriventre and C. macropomum changed δ¹³C levels, while the δ¹³C of P. nigricans and C. macropomum shifted spatially. The contribution of C₄ to the fisheries yield was small. C³ plants (excluding phytoplankton) also contributed less than expected. This was explained by the importance of detritivores to the yield of the fisheries and the dependence of these species on algal carbon.     

Carbon source and trophic position of pelagic fish in coastal waters of south-eastern Izu Peninsula,Japan, identified by stable isotope analysis

ABSTRACT:   It is important to clarify trophic dynamics in marine ecosystems for management of the fishing ground. Organic carbon sources and trophic position of pelagic fishes in the coastal waters of the south-eastern Izu Peninsula, Japan, were examined on the basis of carbon and nitrogen stable isotope distributions. The δ¹³C of the fishes was mostly distributed from −19 to −16‰ for nektonic fishes (13 species of adults and immatures) and planktonic fishes (10 species of larvae and juveniles), close to the δ¹³C values of particulate organic matter and planktonic decapods. These δ¹³C signatures for the inhabitants of the water column were in contrast with the high δ¹³C values (mainly −16 to −13‰) for demersal fishes of Scorpaeniformes and benthic polychaetes collected in the surf zone. These results indicate that nektonic and planktonic fishes depend on phytoplankton for carbon supply. The δ¹⁵N signatures suggest that the trophic position ranged 3.1–4.5 for the nektonic fishes and 2.9–3.7 for the planktonic fishes, premised on trophic level 3 for larval Japanese anchovy Engraulis japonicus . Thus, planktivorous fishes should be mainly assigned to trophic levels 3 and 4 in this area.     

Stable carbon and nitrogen isotopic evidence for ecotonal coupling between boreal forests and fishes

Abstract— As a result of water turbulence effects on boundary layer diffusion resistance and carbon isotopic discrimination, the δ¹³C values (ratios of ¹³C: ¹²C) of attached algae may often overlap those of terrestrial plants, thereby making it impossible to distinguish between the relative importance of these two potential food sources for aquatic animals. The present study used a dual isotope approach (δ¹³C and δ¹⁵N) to refine measurements of the incorporation of allochthonous organic matter into freshwater fishes. The dependence of five species of littoral fishes on terrestrial detritus for part of their energy sustenance was demonstrated. The littoral zones of boreal Canadian Shield lakes are, therefore, not isolated from their surrounding riparian forests in terms of carbon flow as present day timber management guidelines erroneously assume, but instead exhibit a measurable degree of ecotonal land-water coupling. As a result, clearcut logging of riparian forests to the lakeshore edge, permissible by law in most Canadian provinces containing boreal forests, may have to be reassessed as a forest harvesting strategy.     

The dietary regime of detritivorous fish from the River Jacaré Pepira, Brazil

The diet of detritivorous fish was analysed at four distinct habitats in a tropical river during the wet and dry seasons. Two methodologies were used to determine the diet of the fish: (1) the direct analysis of the stomach contents; and (2) the use of stable carbon isotopes. Both methods indicated food partitioning among the fish. The stomach contents showed what the fish had ingested when captured and the ¹³C isotope indicated what it had assimilated over a long period of time. The ¹³C isotope suggested the existence of sectional differences in the feeding of the detritivorous fish along the river. Plants employing the C₄ photosynthesis pathways seem to have little influence on the diet of these fish. This method proved to be more appropriate for the detection of the main food sources of the captured fish.     

Preliminary investigations on the effects of dietary lipid on the spawning performance and egg quality of black sea bass Centropristis striata L

Adult black sea bass Centropristis striata broodstock ( N =162) were fed three different dietary treatments: two commercially prepared diets with 45% protein and two different lipid levels (12% and 20%) (diets 1 and 2), and a diet of frozen Atlantic silversides Menidia menidia (SS, diet 3). Broodstock were held under controlled photothermal conditions and induced to spawn with an LHRHa pellet (72 μg kg⁻¹ bw). Dietary lipid had pronounced effects on spawning performance and egg quality. Diet 3 (SS) produced a significantly ( P <0.05) higher fertilization success (22.4%) than diets 1 (0.6%) and 2 (4.8%). The hatching success of fertilized eggs was similar in all diets (range=40–58.6%), but only two spawns from diet 1 (12% lipid) yielded viable yolk-sac larvae (YSL). Diet 3 (SS) also produced significantly more YSL per female (21.8 × 10³) than the diet 1 (0.3 × 10³). Eggs from diet 3 (SS) contained a significantly greater proportion of n-3 series fatty acids, with docosahexaenoic acid (DHA) as the largest fraction. Eggs from commercially prepared dietary treatments contained significantly more n-6 fatty acids. The poor spawning performance of fish fed diet 1 (12% lipid) may be related to higher levels of linoleic acid and lower levels of DHA in the diet.     

Re-evaluation of vitamin E supplementation of practical diets for channel catfish, Ictalurus punctatus, production

A 10-month feeding trial was performed with channel catfish, Ictalurus punctatus , to re-evaluate the minimum level of dietary vitamin E supplementation required under conditions of commercial production. Four levels (0, 15, 30 and 60 mg kg⁻¹ diet) of supplemental vitamin E were added as DL -α-tocopherol acetate to a typical commercial catfish diet. Sixteen 0.04-ha ponds were stocked in July, at a rate of 25 000 fish ha⁻¹, with two size classes (averaging 18 and 265 g fish⁻¹) of fingerling channel catfish, and each diet was fed to fish in four replicate ponds once daily to satiation. After 10 months of feeding, a total harvest was performed to obtain final production data, and samples were obtained from fish in all ponds. Liver and plasma samples were obtained for α-tocopherol determination, and liver, heart and muscle samples were processed for histological evaluation.
No discernible differences occurred among fish fed the different diets with respect to weight gain or survival. Mean production rate was 9734 kg ha⁻¹, with a final average fish weight of 0.53 kg. A significant ( P < 0.05) effect of diet was noted in plasma and liver α-tocopherol levels, which increased with dietary supplementation. An effect of size also was apparent, with plasma and liver α-tocopherol levels being higher in larger fish compared with smaller fish within a dietary treatment. Histological evaluation revealed no differences among fish fed the different dietary treatments. Based on the lack of overt histological signs of deficiency, it appears that the current level of vitamin E supplementation of commercial catfish diets may be reduced considerably with no detriment to channel catfish health or production.     

Cortisol response of golden shiners (Notemigonus crysoleucas) fed diets differing in lipid content

The purpose of this study was to characterize the plasma cortisol response in golden shiners (Notemigonus crysoleucas) under crowding stress, and to determine whether dietary lipid affects the cortisol response. The main differences between the diets were the relative amounts and types of fatty acids of the n-3 and n-6 families. In experiment 1, triplicate groups of golden shiners were fed diets with 4 or 13% menhaden fish oil, or 4 or 13% poultry fat at 3% body weight for 4 weeks before the crowding stress. In experiment 2, fish were fed diets with 8% lipid from soybean oil (SBO), cod liver oil (CLO), (SBO+CLO), or cottonseed oil (CSO) for 6 weeks before the stress test. Plasma cortisol was measured initially, two hours after the stressor was applied, and two hours after the stressor was removed. The overall pattern of the cortisol response was similar to that seen in other warmwater fishes, but the rate and magnitude of the response were not affected by diet in either experiment. Golden shiners have an intermediate cortisol response compared to other fish that have been exposed to similarly stressful conditions.     

Golden Shiner Notemigonus crysoleucas× Rudd Scardinius erythrophthalmus Hybrids: Gonad Histology and Spawning Trials

Hybrid fish were produced in ponds by crossing golden shiners × rudd ( Notemigonus crysoleucas × Scardinius erythrophthalmus ) and rudd × golden shiners. Histologically, testes from the hybrids contained spermatocytes that resembled those of the parental species, but no sperm were observed. Lack of sperm in hybrids could have been a seasonal effect. The ovaries of both types of hybrids contained variable numbers of morphologically normal, vitellogenic oocytes and numerous abnormal oocytes in the chromatin nucleolar stage. Abnormal oocytes were necrotic or had irregularly shaped nuclei and clumped chromatin. Many oocyte nests contained infiltrating macrophnges. Spawning trials with F₁ hybrids did not result in spawning behavior or production of F₂ generation fish. Colden shiner × rudd hybrids are of reduced fecundity, but sterility was not conclusively demonstrated.     

Growth and condition of marron Cherax tenuimanus fed pelleted diets of different stability

Six groups of 0 + marron Cherax tenuimanus were reared on commercial marron diets based on two different fish meals in a study lasting 4 months. Both diets were prepared in a stable and an unstable pelleted form. Matron fed with koi carp or salmon diet and unfed were used as reference groups. Matron were reared communally in tanks (5 m⁻²) and individually in an intensive crayfish culture system (ICCS, 25 m⁻²). Marron were fed at the rate of 6.5% of their body weight per week. Groups fed with stable diets showed larger weight increment at moult, shorter intermoult period, and higher specific growth rate than groups fed with similar unstable diets. Stable matron diets resulted in faster growth than fish diets. There were no differences in hepatopancreatic indices of marron fed with stable diets or similar unstable diets in the ICCS. The condition of hepatopancreata of marron reared in communal tanks were better than those of marron reared in the ICCS on a similar diet. Results indicate that marron production can be improved using stable pelleted diets in both intensive and semi-intensive culture.     

Linking migratory patterns and diet to reproductive traits in female brown trout (Salmo trutta L.) by means of stable isotope analysis on ova

Abstract –  Many populations of vertebrates display alternative reproductive strategies involving delays in maturation processes and migrations to more productive habitats. Notably for females, migratory patterns and diet could influence reproductive traits such as ova size and number. To test this hypothesis, we targeted anadromous and freshwater-resident female brown trout of various sizes during their return to spawn in tributaries, and carried out stable isotope analyses (δ¹⁵N and δ¹³C) on ova to identify their feeding areas and diet. The study was performed in the Oir River (France), a small coastal system where trout migrations to sea and within the river basin have been monitored for the last 20 years. General trends were observed in reproductive traits, such as the positive correlation between female fork length, fecundity and ova size. Fecundity was size-dependent whatever the migratory origin of females, but major divergences were seen for ova size and isotopic ratios. Freshwater residents displayed a constant increase in ova size and a ¹⁵N-enrichment in ova, suggesting an investment in larger ova and a shift to piscivory as the fish become larger and older. Conversely, anadromous females had smaller ova compared with freshwater-resident females of similar body size and achieved higher fecundity as they grew bigger. Our results suggest the existence of a continuum of reproductive traits for freshwater-resident females whereas anadromous females clearly show a break with this continuum. This major dissimilarity could be explained by the difference in growing environments in terms of food availability and quality.     

Utilization of terrestrial organic matter by the bivalve <Emphasis Type="Italic">Corbicula japonica</Emphasis> estimated from stable isotope analysis

ABSTRACT:   Carbon and nitrogen isotopic ratios in tissue of the bivalve corbicula ( Corbicula japonica ) and particulate organic matter (POM) were measured along a salinity gradient in the Kushida Estuary, Japan. The bivalve exhibited a gradual isotopic enrichment from the uppermost estuarine site (δ¹³C = −24.8‰ and δ¹⁵N = 8.6‰) to the marine site (δ¹³C = −16.1‰ and δ¹⁵N = 11.8‰). Using the concentration-weighted mixing model, the bivalves' food source is estimated from the isotope values for the bivalves and POM from terrestrial plants, marine phytoplankton and benthic microalgae. The results indicated that the contributions of benthic micro algae and phytoplankton were small, while terrestrial particulate matter is significantly important for the corbicula diet, although the contribution varies among sampling sites.     

Changes in skin colour and cortisol response of Australian snapper Pagrus auratus (Bloch & Schneider, 1801) to different background colours

A two-factor experiment was carried out to investigate the change in skin colour and plasma cortisol response of cultured Australian snapper Pagrus auratus to a change in background colour. Snapper (mean weight=437 g) were held in black or white tanks and fed diets containing 39 mg unesterified astaxanthin kg⁻¹ for 49 days before being transferred from white tanks to black cages (WB) or black tanks to white cages (BW). Skin colour values [ L ^* (lightness), a ^* (redness) and b ^* (yellowness)] of all snapper were measured at stocking ( t =0 days) and from cages of fish randomly assigned to each sampling time at 0.25, 0.5, 1, 2, 3, 5 and 7 days. Plasma cortisol was measured in anaesthetized snapper following colour measurements at 0, 1 and 7 days. Fish from additional black-to-black (BB) and white-to-white (WW) control treatments were also sampled for colour and cortisol at those times. Rapid changes occurred in skin lightness ( L ^* values) after altering background colour with maximum change in L ^* values for BW and WB treatments occurring within 1 day. Skin redness ( a ^*) of BW snapper continued to steadily decrease over the 7 days ( a ^*=7.93 × e^{−0.051 × time}). Plasma cortisol concentrations were highest at stocking when fish were held at greater densities and were not affected by cage colour. The results of this study suggest that transferring dark coloured snapper to white cages for 1 day is sufficient to affect the greatest benefit in terms of producing light coloured fish while minimizing the reduction in favourable red skin colouration.     

Effects of the probiotic, Lactobacillus acidophilus, on the growth performance, haematology parameters and immunoglobulin concentration in African Catfish (Clarias gariepinus, Burchell 1822) fingerling

This experiment was carried out to evaluate the effects of the probiotic, Lactobacillus acidophilus , on the growth performance, haematology parameters and immunoglobulin concentration in African catfish Clarias gariepinus fingerling. Two experimental diets were formulated to contain 35 g kg⁻¹ crude protein and 10 g kg⁻¹ lipids accordingly and fed three times daily for 12 weeks to 25 C. gariepinus fingerlings per fibreglass tank in 12 replicates each. The control diet was prepared with no probiotic supplementation whereas the second diet was prepared supplemented with a probiotic, L. acidophilus , containing about 3.01 × 10⁷ colonies/g of diet. The results show that growth performance [specific growth rate (SGR) and relative growth rate (RGR)], nutrient utilization [protein efficiency ratio (PER) and feed conversion ratio (FCR)] and survival were significantly ( P <0.05) higher in fish maintained on the probiotic-supplemented diet compared with those on the control diet. Haematology parameters (packed cell volume, haemoglobin, erythrocyte sedimentation rate, red blood cell and white blood cell, total serum protein, Ca²⁺, Mg²⁺, Cl⁻, glucose and cholesterol) and total immunoglobulin concentrations were also significantly better in fish fed the probiotic-supplemented diet than in the control. Although the water quality parameters monitored were better in the fish fed the probiotic-supplemented diet than in the control, the parameters were not significantly different ( P >0.05). From the results of this experiment, we conclude that L. acidophilus can be used as a probiotic agent in African catfish culture, to enhance fish health, survival and better feed efficiency and growth performance.     

Dietary threonine requirement of juvenile hybrid striped bass (Morone chrysops♀×M. saxatilis♂)

Two growth studies were conducted to determine the dietary threonine requirement of reciprocal cross hybrid striped (sunshine) bass. Semipurified diets were prepared with crystalline amino acids and lyophilized fish muscle to supply 350 g crude protein kg⁻¹ diet. The basal diet contained 4.9 g threonine kg⁻¹ from fish muscle, and test diets were supplemented with graded levels of L-threonine. In the first experiment, fish initially averaging ≊ 9.8 g each were fed diets containing threonine levels of 4.9, 7.5, 10.0, 12.5, 15.0 and 17.5 g kg⁻¹ dry diet for 7 weeks. Weight gain, feed efficiency and protein efficiency ratio (PER) were significantly ( P < 0.01) influenced by dietary threonine level. Based on weight-gain responses, a threonine requirement (± SE) of 8.4 (± 0.8) g kg⁻¹ dry diet was determined, and dietary threonine levels of 10.0 g kg⁻¹ diet or greater resulted in the highest levels of free threonine in plasma.
Based on the results of the first experiment, a second feeding trial was conducted with diets containing threonine levels of 4.9, 6.5, 8.0, 9.5, 11.0 and 12.5 g kg⁻¹ dry diet. Fish initially averaging ≊ 3.0 g each were fed each diet for 8 weeks. Weight gain, feed efficiency and PER values of fish were markedly improved, with increases in dietary threonine up to 8.0 g kg⁻¹ dry diet. Regression analysis of weight gain, feed efficiency and PER data using the broken-line model resulted in threonine requirement estimates of 9.7, 8.5 and 8.6 g kg⁻¹ dry diet, respectively. Based on these data, the threonine requirement of juvenile sunshine bass was determined to be ≊ 9.0 g kg⁻¹ dry diet or 26 g kg⁻¹ of dietary protein.     

Pharmacokinetics of Dietary 13C-Labeled Docosahexaenoic Acid and Docosapentaenoic Acid in Red Sea Bream Chrysophrys major

The objectives of this study were to investigate: 1) the pharmacokinetics of dietary docosahexaenoic acid (DHA) and docosapentaenoic acid (DPA) using ¹³C-labeled fatty acids; 2) the interorgan transport of DHA in the red sea bream by monitoring the DHA level of several organs; and 3) the relationship between the plasma DHA level and optimum dietary DHA level in the plasma of the red sea bream Chrysophrys major . For this purpose, a mixture of 38.5% of [¹³C]DHA, 8.5% of [¹³C]DPA, and 4.2% of [¹³C]palmitic acid were given to the red sea bream at dose level of 8.0, 16.0, and 47.9 mg/kg by a single oral administration. For [¹³C]DHA, the maximum plasma concentration (t_max) occurred at 2.00–3.00 h after the oral administration. The peak plasma concentration (C_max) and the area under the plasma concentration-time curve to 24 h (AUC_0-24 for [¹³C]DHA level linearly increased with respect to dosage. [¹³C]DHA appeared in each organ (plasma, erythrocyte and the fat body of the orbit, liver, intestine, skin, brain, heart and muscle) at 0.5 h and was observed until 24 h. From the values determined for the pharmacokinetic parameters, the range of the effective plasma DHA level for normal growth of the red sea bream was suggested to be between 21.0 and 40.3 μg/mL. For [¹³C]DPA, the AUC_0-24 and C_max values also linearly increased with the dosage, but t_max did not depend on it.