Differences in fatty acid composition of egg capsules from broodstock spotted babylon, <Emphasis Type="Italic">Babylonia areolata</Emphasis>, fed a local trash fish and formulated diet under hatchery conditions

This study is the first attempt to condition broodstock Babylonia areolata using formulated diets under hatchery conditions. Samples of spotted babylon egg capsules from broodstock fed either a formulated diet or a local trash fish, carangid fish (Seleroides leptolepis) for 120 days were analyzed for proximate composition and fatty acid composition. The formulated diet contained significantly higher levels of arachidonic acid (20:4n − 6; ARA), eicosapentaenoic acid (20:5n − 3; EPA) and docosahexaenoic acid (22:6n − 3; DHA) than those of the local trash fish. The formulated diet also had significantly higher ratios of DHA/EPA and (n − 3)/(n − 6) PUFA than those of local trash fish but not for the ARA/EPA ratio. The compositions of egg capsules produced from broodstock fed formulated diet contained significantly more ARA, EPA and DHA compared to broodstock fed the local trash fish. The ARA/EPA and DHA/EPA ratios in egg capsules were significantly higher in the trash fish—fed group compared to those fed the formulated diet. However, (n − 3)/(n − 6) PUFA ratios in egg capsules produced from broodstock fed the formulated diet did not differ significantly compared to those from broodstock fed the local trash fish. The relatively low DHA/EPA, ARA/EPA and (n − 3)/(n − 6) ratios in the egg capsules produced from the formulated diet—fed broodstock B. areolata suggested that this diet is inferior, when compared to the traditional food of trash fish.     

Cod liver oil: feed oil influences on fatty acid composition

The influence of feed oils on fatty acid compositions of cod liver oils was examined to investigate how fatty acid profiles are modified, and to provide estimates of feed oil compositions needed to give liver oils meeting production guidelines [3–11% 18:2n−6, 7–16% 20:5n−3 (EPA) and 6–18% 22:6n−3 (DHA)]. Attention was directed to examination of cod liver oil contents of n−6 and n−3 fatty acids, the essential fatty acids. Data, mostly taken from published work, were subjected to regression analysis to investigate the relationships between the percentages of fatty acids (18:2n−6, total n−6 fatty acids, 18:3n−3, 20:5n−3, 22:6n−3 and total n−3 fatty acids) in feed oils and their percentages in liver oils.     

Effects of salinity on the fatty acid compositions of total lipid and individual glycerophospholipid classes of Atlantic salmon (Salmo salar) and turbot (Scophthalmus maximus) cells in culture

Cells from a relatively stenohaline marine species, turbot (Scophthalmus maximus) (TF) and an anadromous species, Atlantic salmon (AS) were cultured in media supplemented with NaCl to produce OPs varying from 300 to 500 mOsm kg^–1 and the direct effects of OP (salinity) on the fatty acid compositions of the main glycerophospholipid classes were determined. The most dramatic effects of salinity on total lipid fatty acids were observed in polyunsaturated fatty acids (PUFA) in TF cells. There was a graded decrease in the percentage of 18:2n-9, and consequently total n-9 PUFA, and concomitantly increased percentages of both total n-3 and n-6 PUFA with increasing salinity. The increased n-3 and n-6 PUFA was due to significantly increased percentages of the major fatty acids in each of these groups, namely 22:6n-3 and 20:4n-6, respectively. The reciprocal changes in n-9 PUFA and n-3/n-6 PUFA in TF cell total lipid resulted in the percentage of total PUFA not being significantly affected by changes in salinity. The graded decrease in 18:2n-9 with increasing salinity in TF cells was observed in all the major glycerophospholipids but especially PE, PI and PS. Increasing salinity resulted in graded increases in the percentages of 22:6n-3 in PE and PS in TF cells. The quantitatively greatest increase in the percentage of n-6 PUFA in TF cells occurred with 20:4n-6 in PC, PE and PL. There were less significant changes in the fatty acid compositions of glycerophospholipids in AS cells. However, the proportion of total n-3 + n-6 PUFA in PE varied reciprocally with the proportion of dimethylacetals in response to salinity. Similar reciprocal changes between fatty acids in response to salinity were also evident in the quantitatively more minor glycerophospholipids PS and Pl. In PS, the percentage of 22:6n-3 was significantly lower at 400 mOsm kg^–1 whereas the proportion of total monoenes was significantly higher at that salinity. A similar inverse relationship between total monoenes and 20:4n-6 (and, to a lesser extent total saturates) in response to salinity was noted in PI. The results show that environmental salinity, without whole-body physiological stimuli, has direct effects on the fatty acid composition of major glycerophospholipid classes in fish cells and that these effects differ in cells from different fish speciesAbbreviations ANOVA analysis of variance - BHT butylated hydroxytoluene - BSA bovine serum albumin - DMA dimethylacetals - EMEM Eagle's minimal essential medium - FCS fetal calf serum - GC gas chromatography - HBSS Hank's balanced salt solution (without Ca²⁺ and Mg²⁺) - OP osmotic pressure - PC phosphatidylcholine - PE phosphatidylethanolamine - PI phosphatidylinositol - PS phosphatidylserine - PUFA polyunsaturated fatty acid - TLC thin-layer chromatography     

Changes in some components of the muscle lipids of three freshwater fish species under natural extreme cold and temperate conditions

Fatty acid composition, conjugated linoleic acid and cholesterol contents in the muscles of three freshwater fish species (Barbus plebejus escherichi, Capoeta capoeta capoeta and Rutilus rutilus) were determined under natural extreme temperate (July) and cold (January) conditions. The aim of the study was to determine whether there were differences in these components of the muscle lipids among these three fish species under extreme natural conditions. Samples were analyzed using gas chromatography. Palmitic, oleic, docosahexaenoic and eicosapentaenoic acids were the predominant fatty acids in all fish in both months. The percentages of polyunsaturated fatty acids, n − 3 polyunsaturated fatty acids, n − 6 polyunsaturated fatty acids and eicosapentaenoic + docosahexaenoic acids in the muscle of B. plebejus escherichi and C. capoeta capoeta were significantly higher in January (P < 0.05) than in July. The ratio of n − 6 to n − 3 polyunsaturated fatty acids was lower than 0.60 in all fish species, with C. capoeta capoeta showing the lowest ratio in January (0.36). The levels of cholesterol and conjugated linoleic acid ranged from 103.46 to 150.10 mg/100 g oil and from 16.27 to 35.45 mg/100 g oil, respectively, for all samples in both months. There were no statistical differences in cholesterol levels among the three fish species in July and January. Conjugated linoleic acid contents were significantly higher in January in B. plebejus escherichi and C. capoeta capoeta. Of the three species tested, the extreme temperate and cold conditions affected B. plebejus escherichi the most.     

Regulation of growth, fatty acid composition and delta 6 desaturase expression by dietary lipids in gilthead seabream larvae (Sparus aurata)

The Δ6 and Δ5 desaturases and elongases show only very limited activity in marine fish, and little is known of the possibility of enhancing Δ6 desaturase gene expression in these fish. The use of plant oils in marine fish diets is limited by their lack of n−3 highly unsaturated fatty acids (HUFA) despite an abundant content of the 18C fatty acid precursor linoleic and α-linolenic acids. The objective of the present study was to determine the ability of larval gilthead seabream to utilize vegetable oils and assess the nutritional regulation of Δ6 desaturase gene expression. Seventeen-day-old gilthead seabream larvae were fed during a 17-day period with one of four different microdiets formulated with either sardine fish oil (FO), soybean, rapeseed or linseed oils, respectively, or a fifth diet containing defatted squid meal and linseed oil. Good larval survival and growth, both in terms of total length and body weight, were obtained by feeding the larvae either rapeseed, soybean or linseed oils. The presence of vegetable oils in the diet increased the levels of 20:2n−9 and 20:2n−6, 18:2n−9, 18:3n−6, 20:3n−6 and 20:4n−6, in larvae fed rapeseed and soybean oils in comparison to those fed FO. In addition, a sixfold increase in the relative expression of Δ6 desaturase-like gene was found in larvae fed rapeseed and soybean oils, denoting the nutritional regulation of desaturase activity through its gene expression in this fish species. However, feeding linseed oil did not increase the expression of the Δ6 desaturase gene to such a high extent.     

Effects of salinity on the growth and lipid composition of Atlantic salmon (Salmo salar) and turbot (Scophthalmus maximus) cells in culture

The direct effects of osmotic pressure (salinity) on growth performance and lipid composition were investigated in fish cells in culture. Cell lines from a relatively stenohaline marine species, turbot (Scophthalmus maximus) (TF) and an anadromous species, Atlantic salmon (AS) were cultured in media supplemented with NaCl to produce osmotic pressures varying from 300 to 500 mOsm kg⁻¹. The growth rates of the two cell lines were affected in a similar manner by the salinity of the media with the rank order for both peak cell numbers and growth rates up to the day of peak cell number being 300 > 350 > 400 > 450 > 500 mOsm kg⁻¹. Cell death occurred in both cell lines in older cultures at all salinities with the greatest loss of viable cells in media of 300 and 350 kg⁻¹. However, there were quantitative and qualitative differences between the cell lines in their lipid metabolism in response to the salinity of the media. The lipid content expressed per cell showed a positive correlation between lipid per cell and salinity in TF cells, but this was less apparent in AS cells. The percentage of total polar lipid classes increased with increasing salinity in TF cells due mainly to graded increases in the percentages of choline phospholipids. In contrast, there were no significant differences in the proportions of polar and neutral lipid classes with salinity in AS cells. The only significant effect of salinity in AS cells was a decreased proportion of dimethylacetals in total lipid at the highest salinity. The same significant effect of salinity on dimethylacetal content of total lipid was observed in TF cells. However, in addition there was a graded decrease in the percentage of 18:2n-9 in TF cell total lipid with increasing salinity. This was accompanied by increased percentages of total n-3 and n-6 PUFA with higher proportions of both groups of PUFA at 450 and 500 compared with 300 mOsm kg⁻¹. The results show that environmental salinity, in the absence of hormonal or other physiological stimuli, has direct effects on the growth and lipid metabolism of fish cells and that these effects differ in cells from different fish species.     

Application of non-invasive techniques to differentiate sea bass (<Emphasis Type="Italic">Dicentrarchus labrax</Emphasis>, L. 1758) quality cultured under different conditions

European sea bass, Dicentrarchus labrax, is one of the main species cultured in Europe. In this study, non-invasive techniques such as visible-near infrared spectroscopy and dynamometric analysis were used to discriminate concrete tank–cultured sea bass from sea cage–cultured sea bass. A total of 198 samples were collected at six time points from 3 Italian fish farms. A partial least squares analysis was conducted on individual animals at 48 and 96 h post-mortem to determine whether textural and spectral parameters can discriminate between concrete tank– and sea cage–reared sea bass. The results of this analysis demonstrated that spectral measurements better discriminate individual animals at 48 h post-mortem (87% in the independent test) with respect to 96 h post-mortem (66.7% in the independent test). Differences in texture were observed between the two groups of fish, but the texture changed in the time. The texture in sea cage–cultured fish showed higher values of measured force (N) with respect to fish reared in concrete tanks at 48 h post-mortem. Instead, opposite results were observed at 96 h post-mortem. Fillet colour were influenced by both farm and rearing condition.     

Investigation of highly unsaturated fatty acid metabolism in the Asian sea bass, <Emphasis Type="Italic">Lates calcarifer</Emphasis>

Lates calcarifer, commonly known as the Asian sea bass or barramundi, is an interesting species that has great aquaculture potential in Asia including Malaysia and also Australia. We have investigated essential fatty acid metabolism in this species, focusing on the endogenous highly unsaturated fatty acid (HUFA) synthesis pathway using both biochemical and molecular biological approaches. Fatty acyl desaturase (Fad) and elongase (Elovl) cDNAs were cloned and functional characterization identified them as ∆6 Fad and Elovl5 elongase enzymes, respectively. The ∆6 Fad was equally active toward 18:3n-3 and 18:2n-6, and Elovl5 exhibited elongation activity for C_18–20 and C_20–22 elongation and a trace of C_22–24 activity. The tissue profile of gene expression for ∆6 fad and elovl5 genes, showed brain to have the highest expression of both genes compared to all other tissues. The results of tissue fatty acid analysis showed that the brain contained more docosahexaenoic acid (DHA, 22:6n-3) than flesh, liver and intestine. The HUFA synthesis activity in isolated hepatocytes and enterocytes using [1-¹⁴C]18:3n-3 as substrate was very low with the only desaturated product detected being 18:4n-3. These findings indicate that L. calcarifer display an essential fatty acid pattern similar to other marine fish in that they appear unable to synthesize HUFA from C₁₈ substrates. High expression of ∆6 fad and elovl5 genes in brain may indicate a role for these enzymes in maintaining high DHA levels in neural tissues through conversion of 20:5n-3.     

Effects of replacement of dietary fish oil with soybean oil on growth performance and tissue fatty acid composition in marine herbivorous teleost Siganus canaliculatus

Fish oil (FO) substitution has been studied in many marine carnivorous fish, but seldom in marine herbivorous or omnivorous species. To evaluate the feasibility of using soybean oil (SO) as a dietary lipid and confirm its capability of converting C₁₈ polyunsaturated fatty acid (PUFA) into long chain polyunsaturated fatty acid (LC‐PUFA) in the marine herbivorous teleost Siganus canaliculatus, juvenile fish were fed with four formulated diets differing in lipid composition, with SO accounting for 0.76% (SO0), 23% (SO23), 45% (SO45) and 67% (SO67) of total dietary lipid respectively. After feeding for 8 weeks, growth performance including weight gain, specific growth rate, feed conversion ratio and protein efficiency rate were better in the SO23 and, especially, SO45 groups than in the SO0 and SO67 groups (P < 0.05). Tissue fatty acid compositions were affected by diet, with the liver contents of eicosapentaenoic (EPA), docosapentaenoic (DPA), docosahexaenoic (DHA) acids and total n‐3 PUFA displaying parallel changes with the corresponding dietary fatty acids. While the muscle contents of EPA, DPA and total n‐3 PUFA between SO0 and SO23 groups, and the liver contents of arachidonic acid (ARA) and 20:4n‐3, as well as the muscle content of 20:3n‐6 between SO0 and SO45 groups showed no difference, confirming the biosynthesis of LC‐PUFA from C₁₈ precursors in vivo as the contents of corresponding fatty acids in diets SO23/SO45 were much lower than those in diet SO0 (P < 0.05). The results indicate that SO may be a suitable dietary lipid source for S. canaliculatus, and can replace up to 67% or 45% of total dietary FO without negatively compromising growth performance or nutritional quality of fish respectively. Moreover, the study increases our knowledge of FO substitution in marine herbivorous fish.     

Effects of dietary lipid levels on growth performance,feed utilization and fatty acid composition of juvenile Japanese seabass (<Emphasis Type="Italic">Lateolabrax japonicus</Emphasis>) reared in seawater

Triplicate groups of 40 Japanese seabass Lateolabrax japonicus (initial weight, 11.3 ± 0.4 g) reared in seawater (salinity, 30.0–33.0 g L⁻¹) were fed with five isonitrogenous (41.3 ± 0.2% crude protein) and isoenergetic (18.5 ± 0.3 MJ kg⁻¹) experimental diets formulated with increasing lipid levels (4.3, 8.4, 12.2, 15.8 and 20.1% lipid) for 10 weeks. Survival throughout the feeding experiment ranged from 87.5 to 100%, but the survival of fingerlings fed with the 4.3% lipid diet was significantly lower than the rest of the diets. At the end of the feeding experiment, fish fed with 12.2% lipid diet showed optimal growth performance (P < 0.05). Lipid contents of whole body, liver and muscle increased in parallel with the increase in dietary lipid levels. Viscerosomatic index (VSI), hepatosomatic index (HSI) and muscle lipid content were higher in 20.1% lipid group than those in the rest of the lipid level groups indicating that viscera and muscle tissues played important contributions to body lipid deposition. High proportions of 18:1n-9, eicosapentaenoic acid (20:5n-3; EPA) and docosahexaenoic acid (22:6n-3; DHA), and low concentrations of n-6 polyunsaturated fatty acids (PUFAs) occurring in liver and muscle, to some extent, reflected fatty acid (FAs) composition in the experimental diets.     

Ration of 20:3 (n-9) to 20:5 (n-3) in Phospholipids as an Indicators of Dietary Essential Fatty Acid Sufficiency in Striped Bass,Morone saxarilis,and Palmetto Bass,M. saxatilis x M. chrysops

The effects of feeding different sources of brine shrimp nauplii with different fatty acid compositions on growth, survival, and fatty acid composition of striped bass, Morone saxarilis and palmetto bass (M. saxatilis x M. chrysops) were determined. The sources of brine shrimp were Chinese (CH), with a high percentage of 20:5(n-3), eicosapentaenoic acid (EPA), and Colombian (COL), San Francisco Bay (SFB), and Great Salt Lake (GSL), with low percentages of EPA but high percentages of 18:3(n-3), linoienic acid. None of the brine shrimp sources contained a measurable amount of 22:6(n-3), docosahexaenoic acid (DHA). After enrichment with menhaden oil to increase the content of EPA and DHA, the GSL brine shrimp nauplii were also fed to hybrid striped bass.Growth and survival of fish larvae fed brine shrimp nauplii with high percentages of EPA and DHA (CH and GSLE) were higher (P < 0.05) than those of fish fed brine shrimp with a low percentage of EPA (COL, SFB, and GSL). The ratio of 20:3(n-9) eicosatrienoic acid (ETA), to DHA in polar lipids (phospholipids) of fish, traditionally used as an indicator of essential fatty acid (EFA) sufficiency of the diet, was not a reliable indicator of essential fatty acid sufficiency of diets for larval striped bass and hybrid striped bass. However, the ratio of ETA to EPA appears to be an appropriate indicator. An ETA-to-EPA ratio in phospholipids of less than 0.10 is consistent with an EFA sufficient diet.     

Physiology of seawater acclimation in the striped bass,Morone saxatilis (Walbaum)

Several experiments were performed to investigate the physiology of seawater acclimation in the striped bass, Morone saxatilis. Transfer of fish from fresh water (FW) to seawater (SW; 31–32 ppt) induced only a minimal disturbance of osmotic homeostasis. Ambient salinity did not affect plasma thyroxine, but plasma cortisol remained elevated for 24h after SW transfer. Gill and opercular membrane chloride cell density and Na⁺,K⁺-ATPase activity were relatively high and unaffected by salinity. Average chloride cell size, however, was slightly increased (16%) in SW-acclimated fish. Gill succinate dehydrogenase activity was higher in SW-acclimated fish than in FW fish. Kidney Na⁺, K⁺-ATPase activity was slightly lower (16%) in SW fish than in FW fish. Posterior intestinal Na⁺,K⁺-ATPase activity and water transport capacity (J_v) did not change upon SW transfer, whereas middle intestinal Na⁺,K⁺-ATPase activity increased 35% after transfer and was correlated with an increase in J_v (110%). As salinity induced only minor changes in the osmoregulatory organs examined, it is proposed that the intrinsic euryhalinity of the striped bass may be related to a high degree of “preparedness” for hypoosmoregulation that is uncommon among teleosts studied to data.     

Effects of temperature and salinity on oxygen consumption and ammonia excretion of juvenile miiuy croaker, <Emphasis Type="Italic">Miichthys miiuy</Emphasis> (Basilewsky)

The metabolic responses of the juvenile Miichthys miiuy in terms of oxygen consumption and ammonia excretion to changes in temperature (6–25°C) and salinity (16–31 ppt) were investigated. At a constant salinity of 26 ppt, the oxygen consumption rate (OCR) of the fish increased with an increase in temperature and ranged between 133.38 and 594.96 μg O₂ h⁻¹ g⁻¹ DW. The effect of temperature on OCR was significant (P < 0.01). Q₁₀ coefficients were 6.80, 1.41, 1.29 and 2.36 at temperatures of 6–10, 10–15, 15–20 and 20–25°C, respectively, suggesting that the juveniles of M. miiuy will be well adapted to the field temperature in the summer, but not in the winter. The ammonium excretion rates (AER) of the fish were also affected significantly by temperature (P < 0.01). The O:N ratio at temperatures of 6, 10, 15 and 20°C ranged from 13.12 to 20.91, which was indicative of a protein-dominated metabolism, whereas the O:N at a temperature of 25°C was 51.37, suggesting that protein-lipids were used as an energy substrate. At a constant temperature of 15°C, the OCRs of the fish ranged between 334.14 (at 31 ppt) and 409.68 (at 16 ppt) μg O₂ h⁻¹ g⁻¹ DW. No significant differences were observed in the OCR and AER of the juveniles between salinities of 26 and 31 ppt (P > 0.05). The OCR and AER at 16 ppt were, however, significantly higher than those at 26 and 31 ppt (P < 0.05), indicating salinity lower than 16 ppt is presumably stressful to M. miiuy juveniles.     

Comparison of the lipid profiles from wild caught eggs and unfed larvae of two scombroid fish: northern bluefin tuna (<Emphasis Type="Italic">Thunnus thynnus</Emphasis> L., 1758) and Atlantic bonito (<Emphasis Type="Italic">Sarda sarda</Emphasis> Bloch, 1793)

Lipids and essential fatty acids are determinants of the reproductive process in marine fish, affecting fecundity, egg quality, hatching performance, pigmentation and larval malformation. We have analyzed and characterized the lipids of eggs and unfed larvae of two wild caught scombroid fish, the Atlantic northern bluefin tuna (Thunnus thynnus) and Atlantic bonito (Sarda sarda). Dry matter and total lipid contents, polar and neutral lipid classes and total lipid fatty acid contents were determined in the eggs of bluefin tuna and eggs and unfed larvae during the development of Atlantic bonito. Bluefin tuna eggs had slightly but significantly more dry mass than bonito eggs but very similar lipid content. However, bluefin tuna eggs presented a higher polar lipid content due to increased proportions of phosphatidylethanolamine (PE), phosphatidylserine (PS) and phosphatidylinositol (PI). Bonito eggs and larvae showed increasing dry mass and decreasing lipid content with development. The proportion of polar lipids increased due to increased PE, PS and PI, whereas choline-containing polar lipids (phosphatidylcholine and sphingomyelin) remained relatively constant. Free cholesterol also increased, whereas the levels of other neutral lipids, especially triacylglycerol and steryl ester fractions, decreased, presumably due to utilization for energy to drive development. Bluefin tuna eggs had higher levels of n − 3 and n − 6 highly unsaturated fatty acids due to higher docosahexaenoic and arachidonic acid contents, respectively, than bonito eggs. The results are discussed in relation to the lipid and fatty acid requirements of larval scombroid fish in comparison to those of other larval marine finfish species under culture conditions.     

Influence of partial substitution of dietary fish oil by vegetable oils on the metabolism of [1-14C] 18:3n-3 in isolated hepatocytes of European sea bass (Dicentrarchus labrax L.)

The static or declining supply of fish oil from industrial fisheries demands the search of alternatives, such as plant (vegetable) oils, for diets in expanding marine aquaculture. Vegetable oils are rich in C₁₈ polyunsaturated fatty acids but devoid of the n-3 highly unsaturated fatty acids in fish oils. Previous studies, primarily with salmonids, have shown that including vegetable oils in their diets increased hepatocyte fatty acid desaturation. In the present study, we have investigated the effects of dietary partial substitution of fish oil (FO) with rapeseed oil (RO), linseed oil (LO) and olive oil (OO) on the desaturation /elongation and, -oxidation capacities of [1-¹⁴C]18:3n-3 in isolated hepatocytes from European sea bass (Dicentrarchus labrax L.), in a simultaneous combined assay. Fish were fed during 34 weeks with diets containing 100% FO, or RO, LO and OO, each included at 60% with the balance being met by FO, with no detrimental effect upon growth or survival. The highest total desaturation rates were found in hepatocytes of fish fed FO diet (0.52±0.08 pmol/h/mg protein) and OO diet (0.43±0.09 pmol/h/mg protein), which represented 3.2% and 2.7% of total [1-¹⁴C]18:3n-3 incorporated, respectively. In contrast, lowest desaturation rates were presented by hepatocytes of fish fed LO and RO diets (0.23±0.06 and 0.14±0.05 pmol/h/mg protein, respectively) represented 1.4% and 0.9% of total [1-¹⁴C]18:3n-3 incorporated, respectively. The rates of [1-¹⁴C]18:3n-3 β-oxidized were between 11-fold and 35-fold higher than desaturation. However, no significant differences were observed among β-oxidation activities in hepatocytes of fish fed any of the diets. The present study demonstrated that the European sea bass, as a carnivorous marine fish, presented a ‘marine’ fish pattern in the metabolism of 18:3n-3 to 20:5n-3 and 22:6n-3. This species appeared to have all the enzymic activities necessary to produce 22:6n-3 but presented only extremely low rates of fatty acid bioconversion. Furthermore, nutritional regulation of hepatocyte fatty acid desaturation was minimal, and dietary vegetable oils did not increase desaturase activities, and in RO and LO treatments the activity was significantly lower. This revised version was published online in July 2006 with corrections to the Cover Date.     

Long‐chain polyunsaturated fatty acid metabolism in carnivorous marine teleosts: Insight into the profile of endogenous biosynthesis in golden pompano Trachinotus ovatus

Golden pompano Trachinotus ovatus is an important farmed carnivorous marine teleost. Although some enzymes for long‐chain polyunsaturated fatty acid (LC‐PUFA) biosynthesis have been identified, the ability of T. ovatus for endogenous biosynthesis is unknown. Here, we evaluated in vivo LC‐PUFA synthesis in a 56‐day culture experiment using six diets (D1–D6) formulated with linseed and soybean oils to produce dietary linolenic/linoleic acid (ALA/LA) ratios ranging from 0.14 to 2.20. The control diet (D0) used fish oil as lipid source. The results showed that, compared with the corresponding indices of fish fed D0, the weight gain rate and specific growth rate as well as the contents of eicosapentaenoic (EPA) and docosahexaenoic acids in tissues (liver, muscle, brain and eye) of D1–D6 groups were significantly lower (p < .05). These data suggested that T. ovatus could not synthesize LC‐PUFA from C₁₈ PUFA or such ability was very low. However, tissue levels of 20:4n‐3 in fish fed diets D1–D6 were higher than that of D0 fish (p < .05), and positively correlated with dietary ALA/LA ratio, while levels of EPA showed no difference among the D1–D6 groups. These results indicated that Δ5 desaturation, required for the conversion of 20:4n‐3 to EPA, may be lacking or very low, suggesting incomplete LC‐PUFA biosynthesis ability in T. ovatus.     

Effects of dietary macroalgae meal and lipid source on growth performance and body wall fatty acid composition of sea cucumber Apostichopus japonicus

A 70‐day experiment was conducted to examine the effects of different macroalgal meals and lipid sources on growth, body wall composition and fatty acid (FA) profile of sea cucumber Apostichopus japonicus. Two macroalgal meals including Sargassum muticum (SM) and Gracilaria lemaneiformis (GL) and two lipid sources including fish oil (FO) and vegetable oil (VO) were formulated into four diets, i.e., S. muticum and fish oil (SF), S. muticum and vegetable oil (SV), G. lemaneiformis and fish oil (GF) and G. lemaneiformis and vegetable oil (GV). The results showed that the specific growth rates (SGR) of A. japonicus fed diets containing SM were significantly higher than those fed diets containing GL. No significant differences in SGR between the FO‐based and VO‐based groups were observed. Similar results were observed in the body wall lipid content. Most body wall FAs changed to resemble the dietary FA proportions because of the dietary effect. Concentrations of 20:4n‐6 of the SF and GF groups were significantly lower than the SV and GV groups, while levels of 20:5n‐3 and 22:6n‐3 were significantly higher than the SV and GV groups. The n‐3/n‐6 polyunsaturated fatty acids (PUFA) ratios of the SF and GF groups were significantly higher than the SV and GV groups. Moreover, the SF group had significantly higher 20:5n‐3 and 22:6n‐3 contents and n‐3/n‐6 PUFAs ratio than the GF group. These findings reveal that the SF diet can show beneficial effects on both growth performance and body wall n‐3 PUFAs content of A. japonicus.     

Effect of light intensity and photoperiod on biomass and fatty acid composition of the microalgae, Chlorella vulgaris

The effects of irradiance and photoperiod on the biomass and fatty acid (FA) composition of Chlorella vulgaris were examined in the exponential growth phase. Results indicated significant differences in biomass and FA at different intensities and photoperiods. Maximum biomass (2.05 ± 0.1 g l⁻¹) was at 62.5 μmol photons m⁻² s⁻¹ and 16:8 h light/dark photoperiod. FA composition changed considerably in different light regimes; the maximum percentage of total saturated (SFA) (33.38%) was recorded at 100 μmol photons m⁻² s⁻¹ and 16:8 h photoperiod, while monounsaturated (MUFA) and polyunsaturated (PUFA) fatty acids decreased with increasing irradiance and light duration. The maximum percentage of total MUFA (15.93%) and PUFA (27.40%) was recorded at 37.5 μmol photons m⁻² s⁻¹ and 8:16 h photoperiod.     

The fatty acid composition of Nereis diversicolor cultured in an integrated recirculated system: Possible implications for aquaculture

The potential of solid waste originating from a recirculated fish culture system, i.e. faecal material, uneaten food pellets and bacterial biofilms was examined as food source for the marine polychaete Nereis diversicolor. These polychaetes could be a valuable food for fish if they provide essential fatty acids to the fish. Therefore, we analysed the fatty acid profiles from feed and faecal materials, the sediment as well as the cultured organisms — fish and several batches of N. diversicolor — from an integrated recirculating aquaculture system.The major fatty acids (saturated, monounsaturated and polyunsaturated) for all analysed fish feed, fish and faeces samples were C16:0, C18:1 and C22:6 (n − 3), accounting for 48% to 57% of the fatty acids in the samples. The major fatty acids within the sediment were C16:0, C18:1 and C18:3 (n − 3), accounting for 61% of the total fatty acids. The samples of N. diversicolor revealed C16:0, C18:1 and C20:5 (n − 3) as the major fatty acids. Combined, they accounted for 56% of the total fatty acids detected within the worm samples.The results indicate that a recycling or even an upgrade of excreted feed nutrients such as fatty acids, which were otherwise discharged, can be achieved through integrated aquaculture combining fish and worm culture.