Effects of high levels of n−3 HUFA in broodstock diet on egg quality and egg fatty acid composition of Japanese flounder, Paralichthys olivaceus

We investigated the effect of high levels of n−3 highly unsaturated fatty acids (n−3 HUFA) in broodstock diet on egg quality and chemical composition of eggs of Japanese flounder. The broodstock were fed diets containing three levels of n−3 HUFA (2.1%, 4.8% or 6.2%) 2 months before and during the spawning period. No significant difference was found for weight gain of broodstock among the treatments. Egg production was highest in fish fed the highest level of n−3 HUFA. However, egg quality parameters, such as percentage of buoyant eggs, hatching rate and percentage of normal larvae, were significantly higher in the group fed the lowest n−3 HUFA diet. The fatty acid composition of eggs was influenced more markedly in the neutral lipid fraction than in the polar lipid fraction by dietary n−3 HUFA levels. Arachidonic acid (AA; 20:4n−6) and egg quality parameters both decreased with increasing dietary n−3 HUFA levels. The results suggest that a high level of n−3 HUFA in broodstock diet negatively affects egg quality of Japanese flounder.     

Efficacy of dietary methyl esters of n−3 HUFA vs. triacylglycerols of n−3 HUFA by gilthead seabream (Sparus aurata L.) juveniles

A feeding experiment was carried out on gilthead seabream juveniles to investigate the utilization of dietary n−3 highly unsaturated fatty acids (n−3 HUFA), when presented as methyl esters or as triacylglycerols. Three groups of gilthead seabream juveniles, of an initial mean weight of 62 g, were fed diets containing the same level of n−3 HUFA (about 2% dry weight basis, DWB) but where these essential fatty acids (EFA) were supplied in the form of methyl esters, triacylglycerols or as a mixture of these two chemical forms (diets 1, 2 and 3, respectively). A fourth group of 62-g individuals was fed a diet containing a particularly high level of triacylglycerols of n−3 HUFA (about 5% DWB). After 8 weeks of feeding, the results showed that fish growth, hepatosomatic index, total lipid content, and fatty acid composition of neutral and polar lipids of brain, liver, gills and muscle were not affected by the chemical form of the lipids given in the diet. However, individuals fed the very high level of EFA (diet 4) showed a lower growth rate than the other three groups of fish. In addition, eicosapentaenoic acid (EPA; 20:5n−3) and docosahexaenoic acid (DHA; 22:6n−3) levels in both neutral and polar lipids from liver, gills and muscle were higher in this group of fish, with the brain fatty acid composition being less affected by dietary regime.     

Influence of broodstock gilthead seabream (Sparus aurata L.) dietary fatty acids on egg quality and egg fatty acid composition throughout the spawning season

The influence of broodstock dietary lipids on egg quality and egg fatty acid composition throughout the spawning season of gilthead seabream was investigated. For this purpose, the fish were fed for 7 months either a control diet (diet C) or a diet deficient in n−3 highly unsaturated fatty acids (n−3 HUFA) but rich in both oleic (18:1n−9) and linolenic (18:3n−3) acids (diet D). Eggs spawned by both groups of fish were sampled at the beginning, middle and end of the spawning season and the fatty acid composition of their neutral (NL) and polar lipids (PL) determined. In the early season, percentages of fertilized and hatched eggs, relative proportions of NL and PL as well as their fatty acid compositions, were not affected by the lipid composition of the broodstock diet. However, the eggs spawned during the middle and late seasons showed marked differences among the two groups of fish, clearly reflecting the influence of dietary fatty acids. This influence was more evident in the neutral lipid fraction than in the polar lipids. No correlation was found between the number of buoyant eggs and eicosapentaenoic (20:5n−3, EPA), docosahexaenoic (22:6n−3, DHA) fatty acids or total n−3 HUFA contents in egg phospholipids. However, a negative correlation was detected when percentages of fertilized eggs were compared with the levels of 18:1n−9, 18:3n−3 and with the ratio 18:1n−9/n−3 HUFA present in the phospholipids. Our results indicate the importance of maintaining not only the level of n−3 HUFA in egg membrane phospholipids, but also the balance between n−3 HUFA and other fatty acids such as 18:1n−9 and 18:3n−3, in order to obtain a high spawning quality.     

Atlantic salmon, Salmo salar, utilizes wax ester-rich oil from Calanus finmarchicus effectively

Against a background of decreasing availability of fish oils for use in aquaculture, the present study was undertaken to examine whether a wax ester-rich oil derived from the calanoid copepod Calanus finmarchicus, could be used effectively by Atlantic salmon when supplied in their diet. Individually tagged Atlantic salmon of initial weight around 500 g were divided into replicate tanks of two dietary groups and fed either a fish oil supplemented diet, or an experimental diet coated with Calanus oil. Wax esters accounted for 37.5% of the lipids in the Calanus oil diet but were absent from the fish oil diet in which triacylglycerols (TAG) were the major lipid class. Over the feeding period (140 days) the salmon fed fish oil displayed a greater increase in length, but there was no significant difference between the two groups in weight gained. The specific growth rates (0.75) and the feed conversion ratio of fish fed the two diets were similar throughout the study. No differences were observed in the apparent digestibility coefficients (ADC) of fish fed Calanus oil or fish oil. The ADC of fatty acids decreased with chain length and increased with unsaturation. Long-chain alcohol utilization showed a similar tendency although there was a notable difference in that saturated long-chain alcohols were utilized better than the comparable fatty acid homologue. In fecal lipid of fish fed Calanus oil, the content of 16:0 alcohol decreased in both the free long-chain alcohol and wax ester fractions, while the corresponding fatty acid increased in the feces of both dietary groups of fish. In contrast, the proportion of the 22:1n−11 alcohol increased in both fecal wax esters and free long-chain alcohol fractions whereas 22:1n−11 fatty acid displayed no accumulation. The observed patterns of fatty acid and long-chain alcohol compositions in fecal lipid compared to those of the initial dietary lipid are consistent with the digestive lipases of salmon preferentially hydrolyzing esters containing polyunsaturated fatty acid (PUFA) moieties. The wax esters of Calanus oil contained substantial amounts of the n−3 PUFA, 20:5n−3 and 22:6n−3, that were effectively deposited in muscle and liver tissues. No major differences were seen in either lipid content/lipid classes or in gross fatty acid composition of these tissues between the two dietary groups. It is concluded that that Atlantic salmon in seawater can effectively utilize diets in which a major lipid component is derived from zooplankton rich in wax ester without any detrimental change in growth or body lipid composition. This finding gives support to the use of lipid from zooplankton from high latitudes as an alternative or as a supplement to fish oil and a provider of long-chain n−3 PUFA in diets for use in salmon aquaculture.     

Dietary impact of algal and artificial diets, fed at different feeding rations, on the growth and fatty acid composition of Tapes philippinarum (L.) spat

The effect of lipid supplementation and algal ration on growth and fatty acid composition of juvenile clams, Tapes philippinarum was investigated. A diet of Tetraselmis suecica was supplemented with a lipid emulsion and fed at a daily ration of 0.5, 1.0 and 1.5% WW DW⁻¹ day⁻¹. A mixed algal diet of Isochrysis galbana (clone T-Iso) and T. suecica (1:1 on DW basis) and starvation functioned as positive and negative control treatments, respectively. T. suecica, which contains eicosapentaenoic acid (20:5n−3) but no docosahexaenoic acid (22:6n−3), was supplemented with 50% (% of algal dry weight) of a 22:6n−3-rich emulsion. Higher growth rates of T. philippinarum were associated with higher T. suecica feeding rations. Lipid supplementation resulted in significantly better growth rates of T. philippinarum at a T. suecica ration of 0.5, 1.0 and 1.5% WW DW⁻¹ day⁻¹. The growth promoting effect of lipid supplementation was significantly reduced during 4 consecutive weeks or by increasing the algal feeding ration. Increasing T. suecica rations were associated with a decrease in the % composition of 22:6n−3 while the 20:5n−3% composition was hardly affected in the total lipids of T. philippinarum. On the contrary, the absolute concentration of 22:6n−3 (μg per gram dry weight, μg g DW⁻¹) in the total lipids of T. philippinarum was similar at all T. suecica rations while the 20:5n−3 concentration significantly increased. The major effect of lipid supplementation on the fatty acid composition of the clams, was a significant increase of the 22:6n−3% composition in the total lipids, polar lipids and triglycerides. In contrast with 20:5n−3, the effect of lipid supplementation on the absolute 22:6n−3 content (μg g DW⁻¹) was more pronounced at a higher T. suecica ration. After a starvation period of 4 weeks, the concentration (μg g DW⁻¹) of all fatty acids was significantly reduced, except the n−7 monoenoic fatty acids (MUFA) and the non-methylene interrupted dienoic fatty acids (NMID). The concentration (μg g DW⁻¹) of the NMID in starved clams and clams fed different diets was similar to the concentration in the initial sample. This indicated that growing spat was actively synthesising NMID and they were selectively retained in unfed animals. The results indicated that either dietary lipid or 22:6n−3 was a growth-limiting factor when T. suecica was fed at a ration of 0.5, 1 and 1.5% WW DW⁻¹ day⁻¹. A selective retention in starved clams and a preferential accumulation in fed clams was observed for 22:6n−3 but not for 20:5n−3 which indicated a greater importance of 22:6n−3 compared to 20:5n−3.     

Egg and larval quality,and egg fatty acid composition of Eurasian perch breeders (Perca fluviatilis) fed different dietary DHA/EPA/AA ratios

In Eurasian perch (Perca fluviatilis), the variability in spawning quality is a major limiting factor for successful production, especially when breeders are fed with an artificial diet. The influence of the dietary DHA/EPA/AA ratio on the egg and larval quality and on the fatty acid and lipid class composition of eggs has been investigated in perch broodstock. Two experimental diets (16% lipids) with two different DHA/EPA/AA ratios, D1 (3/2/2) and D2 (23/9/1), were compared with a natural diet consisting of cultured carp juveniles, CC (10/10/1) and with a commercial diet for salmonids, CDS (14/16/1). Percentages of fertilization and hatching were comparable between fish fed D1, D2 and CC, with the highest hatching rate observed for D1 (63.5 ± 3.8%). These diets supported better values than the CDS. Larval survival and TL50 observed after osmotic stress were higher for the D1 group, followed by larvae produced by fish fed D2 and CC. Larvae from fish fed D1, D2 and CC were significantly more robust than larvae from the CDS group. Differences were observed regarding the fatty acid (FA) profile in the eggs, which was related to the dietary FA composition. The results indicate that a ratio of 3/2/2 seemed to be effective for obtaining eggs and larvae of good quality.     

Deposition of astaxanthin in fillets of Atlantic salmon (Salmo salar) fed diets with herring, capelin, sandeel, or Peruvian high PUFA oils

To elucidate whether absorption and deposition of dietary astaxanthin are influenced by the use of different dietary fish oils having different melting points and fatty acid profiles, triplicate groups of individually labeled Atlantic salmon (initial average weight 569 g) were reared in 2 m² tanks, supplied with saltwater. The fish were fed four different experimental diets coated with either herring oil, capelin oil, sandeel oil, or a Peruvian oil high in polyunsaturated fatty acids. Salmon fed diets containing Peruvian high PUFA oil had significantly higher (13%) fillet carotenoid content than salmon fed herring oil (P<0.05). Astaxanthin retention was significantly higher (P<0.05) in salmon fed capelin and Peruvian high PUFA oil than in the two other groups. The effects of dietary oil supplements on carotenoid deposition were rather small and require verification. Redness of fillets and blood plasma astaxanthin levels did not differ among treatments. Liver weights, body weights, as well as specific growth rates, and feed conversion ratios were unaffected by dietary oil source. Significant (P<0.05) positive linear relationships were found between final fillet idoxanthin concentration and total saturated fatty acids in supplement oils, astaxanthin and total monounsaturated fatty acids, and redness and total n−3 fatty acids, whereas the relationships between redness and total monounsaturated fatty acids and astaxanthin and total n−3 fatty acids were negative.     

The Effect of Diet on the Biochemical Composition of Juvenile Artemia: Potential Formulations for Rock Lobster Aquaculture

The lipid class and fatty acid (FA) composition of juvenile Artemia fed continuously on four diets—the microalga Tetraselmis suecica , a mix of oat bran-wheat germ-lecithin (OWL), OwL-eicosapentaenoic acid (EPA), and OWL-EPA-arachidonic acid (AA)—were examined over a 9-d experiment in an attempt to approximate the FA profile of phyllosoma larvae of wild southern rock lobster Jasus edwardrii . The main difference in lipid class composition of Artemia fed the four diets was the relative level of polar lipid (PL) and triacylglycerol (TAG). By day 9, the algal-fed Artemia were highest in PL (95% of total lipid) and lowest in TAG (2%), whereas the remaining diets resulted in Artemia with 16–30% PL and 41–82% TAG. After 2 d, the relative FA composition of all Artemia treatments closely reflected those of the diets, with no marked change after further feeding (to day 9). In terms of the content of essential polyunsaturated fatty acids (PUFA), by day 5 Artemia fed: 1) with the algal diet contained 7 mg/g FA dry mass (0.3% DHA, 6.3% EPA, 3.4% AA of total FA); 2) with the OWL diet contained 3 mg/g (0.3% DHA, 0.9% EPA, 0.7% AA); 3) with the OWL-EPA diet contained 55 mg/g (6.2% DHA, 11.6% EPA, 1.1% AA); and 4) with the OWL-EPA-AA contained 83 mg/g (3.8% DHA, 7.5% EPA, 17.4% AA). The PUFA profiles of Artemia using the OWL-oil diets were similar to wild rock lobster phyllmmata, although levels of doco-sahexaenoic acid (DHA) were lower (10% DHA) than in J. edwardsii larvae. On the basis of PUFA composition data alone, the results suggest the suitability of the OWL-oil mixed diets for consideration for feeding to Artemia used in the culture of southern rock lobster larvae, particularly if the level of DHA can be further enhanced.     

Effect of increasing docosahexaenoic acid content in weaning diets on survival,growth and skeletal anomalies of longfin yellowtail (Seriola rivoliana,Valenciennes 1833)

Five isoproteic (54.8%) and isolipidic (24.1%) microdiets, which varied in their docosahexaenoic acid (DHA) content (0.25%, 0.75%, 1.64%, 1.99% and 3.17%; dw), were manufactured to determine its effects on longfin yellowtail Seriola rivoliana larvae in terms of fish biological performance, whole body fatty acid profile and incidence of skeletal anomalies from 30 dah (11.31 ± 1.79 Total Length, TL) to 50 dah (19.80 ± 0.58 mm TL). The inclusion of dietary DHA up to 3.17% (dw) improved larval resistance to air exposure, although DHA did not significantly affect fish final growth or final survival. Indeed, high levels of dietary DHA (1.99% and 3.17%, dw) tended to increase the incidence of skeletal anomalies in S. rivoliana larvae, albeit no significant differences were observed. Furthermore, the occurrence of severe anomalies such as kyphosis and lordosis, was mainly associated to the larvae fed the highest levels of dietary DHA. In terms of survival, increasing dietary DHA levels did not significantly affect longfin yellowtail survival rate, despite a tendency for enhanced survival. The results of the present study proved that the inclusion of dietary DHA in inert diets up to a 3.17% (dw) and a DHA/EPA ratio above 3.1 increased the final survival and stress resistance in S. rivoliana larvae.     

Requirement of n-3 long chain polyunsaturated fatty acids for European sea bass (Dicentrarchus labrax) juveniles: growth and fatty acid composition

European sea bass juveniles (14.4±0.1 g mean weight) were fed diets containing different levels of fish oil then of n-3 highly unsaturated fatty acids (n-3 HUFA) for 12 weeks. The fish performance as well as fatty acid (FA) composition of neutral and polar lipids from whole body after 7 and 12 weeks feeding were studied. The requirements of juvenile sea bass for n-3 highly unsaturated fatty acids (n-3 HUFA) were studied by feeding fish diets containing six different levels of n-3 HUFA ranging from 0.2% to 1.9% of the diet, with approximately the same DHA/EPA ratio (1.5:1).

The growth rate at the end of the trial showed significant differences. Fish fed low dietary n-3 HUFA (0.2% DM of the diet) showed significantly lower growth than the diet 3 (0.7%), then no further improvement (P>0.05) of growth performance was seen by elevating the n-3 HUFA level in the diet up to 1.9% (diet 6). No difference in feed efficiency, protein efficiency ratio or protein retention was observed among treatments, nor in protein and total lipid content. However, the n-3 HUFA levels in diets highly influenced fish fatty acid composition in neutral lipid, while polar lipid composition was less affected. Comparison of polar lipid content after 7 or 12 weeks indicated that DHA remained stable at the requirement level, while arachidonic acid decreased with time. Results of this experiment suggest that the requirement for growth of n-3 HUFA of juvenile sea bass of 14 g weight is at least 0.7% of the dry diet.     

Effects of dietary DHA/EPA ratios on growth performance,survival and fatty acid composition of juvenile swimming crab (Portunus trituberculatus)

This study was conducted to investigate the effects of dietary docosahexaenoic to eicosapentaenoic acid (DHA/EPA) ratios on growth performance, survival and fatty acid composition of juvenile swimming crab (Portunus trituberculatus). Four isonitrogenous and isoenergetic experimental diets were formulated to contain different DHA/EPA ratios (0.70, 0.84, 1.06 and 1.25). There were three replicates (15 crabs per replicate) for each diet treatment. The crabs were fed (about 6–8% body weight) twice daily for 8 weeks. A good growth performance and feed utilization were observed in swimming crabs fed the diets with DHA/EPA ratios of 0.70 and 0.84. Crabs fed diet with 0.70 DHA/EPA ratio showed a significantly higher weight gain (WG) compared with the crabs fed the diet with DHA/EPA ratio of 1.25 (P < 0.05). The result of this study showed that the survival increased with decreasing the ratio of DHA/EPA. The DHA/EPA ratios in polar lipid from tissues were influenced by the dietary DHA/EPA ratios. Results of this study indicated that the growth performance and survival of juvenile swimming crab are correlated to the DHA/EPA ratio in the diets, and the best growth performance and survival were achieved with the ratios of 0.70–0.84.     

Effects of dietary eicosapentaenoic acid on growth, survival, pigmentation and fatty acid composition in Senegal sole (Solea senegalensis) larvae during the Artemia feeding period

We examined the effect of dietary eicosapentaenoic acid (EPA, 20:5n‐3) on growth, survival, pigmentation and fatty acid composition of Senegal sole larvae. From 3 to 40 days post‐hatch (dph), larvae were fed live food that had been enriched using one of four experimental emulsions containing graduated concentrations of EPA and constant docosahexaenoic acid (DHA, 22:6n‐3) and arachidonic acid (ARA, 20:4n‐6). Final proportions of EPA in the enriched Artemia nauplii were described as ‘nil’ (EPA‐N, 0.5% total fatty acids, TFA), ‘low’ (EPA‐L, 10.7% TFA), ‘medium’ (EPA‐M, 20.3% TFA) or ‘high’ (EPA‐H, 29.5% TFA). Significant differences among dietary treatments in larval length were observed at 25, 30 and 40 dph, and in dry weight at 30 and 40 dph, although no significant correlation could be found between dietary EPA content and growth. Eye migration at 17 and 25 dph was affected by dietary levels of EPA. Significantly lower survival was observed in fish fed EPA‐H diet. Lower percentage of fish fed EPA‐N (82.7%) and EPA‐L (82.9%) diets were normally pigmented compared with the fish fed EPA‐M (98.1%) and EPA‐H (99.4%) enriched nauplii. Tissue fatty acid concentrations reflected the corresponding dietary composition. ARA and DHA levels in all the tissues examined were inversely related to dietary EPA. This work concluded that Senegal sole larvae have a very low EPA requirement during the live feeding period.     

Rotifers fed various diets of baker''s yeast and/or Nannochloropsis oculata and their effect on the growth and survival of striped mullet (Mugil cephalus) and milkfish (Chanos chanos) larvae

The rotifer Brachionus plicatilis (S-type Hawaiian strain) was cultured with various combinations of baker's yeast and Nannochloropsis oculata. There were no significant differences in the daily rotifer production and amino acid profiles of the resulting rotifers. The significantly lower levels of fatty acids (C14, C16, C20:4n−6, C20:5n−3 and C22:6n−3) observed in the rotifers were found to correspond with the amount of yeast presented in their diet. The low survival and growth of striped mullet larvae recorded at Day 15 posthatching indicates that rotifers fed only yeast were nutritionally deficient in fatty acids. The fatty acid requirements of mullet, however, appeared to be satisfied with rotifers cultured on a combination of yeast and N. oculata. In contrast, no significant differences in larval milkfish survival and growth at Day 10 posthatching were detected when using rotifers fed the various diets in the larval rearing protocol.     

Effects of dietary protein to energy ratios on growth and body composition of juvenile Japanese seabass, Lateolabrax japonicus

A growth experiment was conducted to determine the optimal dietary protein to energy (P/E) ratio for juvenile Japanese seabass (initial average weight 6.26±0.10 g). Nine practical diets were formulated to contain three protein levels (36%, 41% and 46%), each with three lipid levels (8%, 12% and 16%), in order to produce a range of P/E ratios (from 19.8 to 28.6 mg protein kJ⁻¹). Each diet was randomly assigned to triplicate groups of 60 fish in sea floating cages (1.5×1.5×2.0 m). Fish were fed twice daily (06:30 and 16:30) to apparent satiation for 8 weeks. The water temperature fluctuated from 26.5 to 32.5 °C, the salinity from 32‰ to 36‰ and dissolved oxygen content was approximately 7 mg l⁻¹ during the experimental period. The results showed that the growth was significantly affected by dietary P/E ratio (P<0.05). Fish fed the diets with 46% protein (12% and 16% lipid, P/E ratio of 26.7 and 25.7 mg protein kJ⁻¹) had the highest specific growth rates (SGR) (4.26 and 4.24% day⁻¹). However, fish fed the diet with 41% protein and 12% lipid showed comparable growth (4.20% day⁻¹), and had higher protein efficiency ratio (PER), protein productive value (PPV) and energy retention than other groups (P<0.05). No significant differences in survival were found among dietary treatments. Carcass lipid content positively correlated with dietary lipid level irrespective of protein level and inversely correlated with carcass moisture content. Carcass protein and ash contents increased with increasing dietary lipid at each protein level. These results suggest that the diet containing 41% protein and 12% lipid with P/E of 25.9 mg protein kJ⁻¹ is optimal for Japanese seabass.     

The impact of nutrition on metamorphosis in Atlantic halibut (Hippoglossus hippoglossus L.)

Fatty acids, vitamin A and thyroid hormone have all been shown to affect development of flatfish larvae and they are ligands to nuclear receptors that participate in the control of development. Our hypothesis was that one of these factors or an interaction between them may be the cause of abnormal development of flatfish larvae. Atlantic halibut larvae were fed either DHA-selco-enriched Artemia or copepods from first feeding. In fish that had been fed Artemia, only 7% had normal pigmentation and 10% normal eye migration. The numbers for fish fed copepods were 68% and 88%, respectively. Malpigmented fish fed Artemia were depigmented, while those fed copepods had ambicoloration. The differences in development were probably nutrient dependent, since all other conditions were similar for the two groups. Larvae fed copepods had markedly higher body levels of docosahexanoic acid (DHA, 22:6n−3) and eicosapentaenoic acid (EPA, 20:5n−3) and lower levels of arachidonic acid (ARA, 20:4 n−6) than larvae fed Artemia. The DHA/EPA ratio was similar in the two groups, but the EPA/ARA ratio was more than four times higher in larvae fed copepods than in larvae fed Artemia. Larvae fed copepods had higher body levels of total retinol than larvae fed Artemia, but the difference was due to higher levels of the storage forms, retinyl esters, whereas the levels of free retinol and retinal were similar in the two groups. The level of iodine was 700 times higher in copepods than in Artemia and 3–4 times higher in larvae fed copepods than in larvae fed Artemia. There was a significantly higher level of T₄ in larvae fed copepods during the “window of opportunity”, 15–30 days after first feeding. In an experiment where Atlantic halibut larvae were fed Artemia enriched in iodine up to the levels found in copepods, there was a significant effect on the body level of iodine and a non-significant tendency of higher levels of thyroid hormone, but no effect on pigmentation or eye migration. It is concluded that Artemia probably offers a sufficient access to vitamin A precursors to meet the larval requirement. More research should be done to elucidate possible effects of iodine on development of Atlantic halibut larvae. Fatty acid composition is still the most likely candidate for causing abnormal development in Atlantic halibut larvae.     

Effects of varying dietary docosahexaenoic acid levels on growth,proximate composition and tissue fatty acid profile of juvenile silver pomfrets,Pampus argenteus (Euphrasen, 1788)

This study investigated the effects of varying dietary levels of decosahexaenoic acid (DHA) on growth performance, proximate composition and whole body fatty acid profiles of juvenile silver pomfret, Pampus argenteus. Triplicate groups of fish (30.55 ± 0.08 g) were fed diets containing 5.2%, 9.31% and 13.38% DHA (% of total fatty acids) or 0.85%, 1.52% and 2.18% DHA on dry diet weight for diets 1, 2 and 3 respectively. Survival was not affected by dietary DHA levels. The growth performance and feed utilization parameters of fish fed diets 2 and 3 were significantly (P < 0.05) higher than those fed diet 1, although these parameters in diets 2 and 3 did not differ significantly (P > 0.05). Whole body lipid and fatty acid profiles were influenced by dietary DHA levels. Significantly higher n‐3 fatty acids particularly DHA, DHA:EPA(eicosapentaenoic acid) ratios and n‐3:n‐6 ratios were observed in fish fed diets 2 and 3 compared to those fed diet 1. Better growth performance and higher whole body DHA:EPA (2.31, 2.29) ratios and n‐3:n‐6 ratios (2.17, 2.12) observed in fish fed diets 2 and 3, respectively, suggests that silver pomfret juveniles have a higher requirement for n‐3 fatty acids, notably DHA for optimum growth and survival.     

Optimizing the essential fatty acids, eicosapentaenoic and docosahexaenoic acid, in the diet of the prawn, Penaeus monodon

The dietary requirements of Penaeus monodon for eicosapentaenoic (20:5n‐3; EPA) and docosahexaenoic (22:6n‐3; DHA) acids were examined. These requirements were examined when dietary levels of linoleic (18:2n‐6; LOA) and linolenic acids (18:3n‐3; LNA) were also provided at previously established optimal levels of 14 and 21% respectively of the total lipid fatty acids. A 5 × 5 factorial design was used with incremental amounts (0, 4, 8, 12 and 16% of total fatty acids) of EPA and/or DHA. An additional diet containing cod‐liver oil was provided as a reference diet. The total lipid content of all of the 25 treatments and reference diets was maintained at the same level of 75 g kg^?1. Growth of prawns fed with the reference diet after 50 days was 244 ± 21%. The greatest response to singular additions of EPA or DHA was with a 12% inclusion of either fatty acid, resulting in 287 ± 21 and 293 ± 18% weight gain, respectively. Growth was generally better when combinations of EPA and DHA were used, the optimal combination being EPA 4% and DHA 4%, resulting in 335 ± 25% weight gain. Addition of high levels of either of the highly unsaturated fatty acids (HUFA) in the diet had a negative effect on growth. Digestibilities of the total neutral lipid and specific fatty acids were examined during the growth trials. The digestibility of total neutral lipid was usually higher when either or both HUFA were present, however there were few significant differences between treatments that contained either or both HUFA. Following the growth trials, digestive glands (DG) of prawns fed with the various diets were analysed to determine the total lipid content and fatty acid composition. Total lipid in the digestive gland increased with the inclusion of DHA, but was not significantly affected by the addition of EPA. The fatty acid composition of the digestive gland lipid generally reflected that of the diet. However, the maximum retention of EPA (11.1% of total DG fatty acids) and DHA (10.7% of total DG fatty acids), was not directly proportional to the amount of either fatty acid present in the diet. These results demonstrate that both EPA and DHA have considerable growth promoting capacity. This growth promoting capacity is enhanced when an optimal balance of both fatty acids are incorporated into the diet.     

Importance of dietary arachidonic acid for the growth,survival and stress resistance of larval European sea bass (Dicentrarchus labrax) fed high dietary docosahexaenoic and eicosapentaenoic acids

Together with docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), arachidonic acid (ARA) is being considered to be an essential fatty acid in marine fish larval diets. The objective of the present study was to determine the importance of dietary ARA levels for larval European sea bass performance, when EPA and DHA are also present in the diet. Eighteen‐day‐old larvae were fed, for 14 days, gelatine‐based microdiets containing the following ARA levels: 0.3%, 0.6% or 1.2%. Elevation of dietary ARA up to 1.2% showed a positive correlation with larval survival and a significant improvement in the specific growth rates, body weight and total length. Arachidonic acid was efficiently incorporated into larval lipids, even at a higher proportion than that in the diets. Increased accumulation of ARA did not affect the incorporation of DHA or EPA from the diet into larval total lipids. A significant positive correlation was found between dietary ARA levels and survival after handling stress, indicating the importance of this fatty acid in sea bass larvae response to acute stressors. The results show the importance of ARA for sea bass larvae, but higher dietary levels should be tested to determine whether there is a negative effect of ARA in sea bass as reported for other species.     

Beneficial effects of n-3HUFA enriched Artemia as food for larval palmetto bass (Morone saxatilis × M. chrysops)

The beneficial effects of feeding n−3 highly unsaturated fatty acids (HUFA ≥ 20 carbon fatty acids with three or more double bonds) to palmetto bass (striped bass × white bass) larvae, 4–30 days of age, were studied using Artemia diets enriched with six n-3HUFA levels. Dietary n-3HUFA concentrations were < 0.03% (control diet), 0.33%, 0.63%, 0.87%, 1.26%, and 2.27% of dry-wt Artemia. Larval n-3HUFA contents were reduced at a faster rate with decreasing dietary n-3HUFA intake, and were significantly different by 30 days posthatch (4–20 mg g⁻¹ dry-wt fish). Starved larvae selectively conserved endogenous n-3HUFA reserves, indicating an essential role of n-3HUFA in larval development. Mass mortality in the control and 0.33% n-3HUFA diets occurred at metamorphosis (26–28 days posthatch). At harvest, all fish, except those fed the two highest n-3HUFA diets, suffered from handling stress (shock syndrome) with increasing severity (25 to 100%) at decreasing dietary n-3HUFA intake. Recovery from shock syndrome was 100% at the 0.63% and 0.87% n-3HUFA diets, 63% at the 0.33% n-3HUFA diet and 0% at the control diet. Post-harvest survival was similar among the four highest dietary n-3HUFA groups (64–73%), whereas the two lowest n-3HUFA groups differed significantly (0 and 37%). Growth promotion was evident with increased dietary n-3HUFA intake as fish fed the highest n-3HUFA diet were twice the size of those fed the control diet (99 vs 52 mg wet-wt). Final fish sizes at the three highest n-3HUFA diets were similar. Given similar culture conditions, a minimum dietary n-3HUFA intake of 1.26% of dry-wt Artermia is recommended to avoid handling stress and promote growth in larval palmetto bass.