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.     

Effect of dietary protein and lipid source on the growth, survival, condition indices, and body composition of marron, Cherax tenuimanus (Smith)

A trial was conducted in 12 purpose-built, commercial, drainable, earthen ponds to evaluate the effect of fish and plant protein and lipid source on the growth, condition indices, and body composition of marron (Cherax tenuimanus). Juvenile marron (1.3±0.28 S.E. g) at the stocking densities of three per square meter were fed for a period of 1 year with four different formulated isoenergetic practical diets (D₁, D₂, D₃, and D₄). Three of the test diets (D₁, D₂, and D₃) were isonitrogenous whereas the fourth test diet (D₄) was protein-free. Protein and lipid sources in D₁ were from Lupin (Lupinus albus) whereas protein and lipid sources in D₂ and D₃ were from fish meal. Fish oil (3.5%) was added to D₁, D₃, and D₄ whereas sunflower oil was added to D₂ and D₄ in order to make them isoenergetic. The four test diets were randomly allocated to three replicate ponds.

The lack of protein in D₄ did not significantly influence (P>0.05) the mean final weight and specific growth rate of marron. Survival was low in all ponds (13.82–34.66%) but feeding with D₄ resulted in a significantly (P<0.05) higher survival than marron fed with D₁ and D₂. Feeding a diet containing a combination of fish protein and fish oil (D₃) resulted in significantly higher (P<0.05) wet tail muscles-to-body weight ratio than was observed with other diets. Tail muscles protein level of all marron was significantly lower (P<0.05) at the end of the trial than at the beginning. EPA and DHA in hepatopancreas and tail muscles of marron were affected by the four test diets. The inclusion of plant protein in formulated diets had a negative impact on the pond environment due to significantly higher unionised ammonia levels that resulted in lower survival. Juvenile marron fed with a plant protein diet had significantly lower protein levels in their hepatopancreas compared to those fed with diets containing animal protein. Feeding marron with lupin protein source (D₁) and plant oil (D₂) for 1 year did not alter the lipid content of their hepatopancreas. Four test diets had no influence on the fat content of marron hepatopancreas; however, these test diets significantly reduced the protein content of the tail muscles of marron.

Environmental variables, particularly temperature, nitrogen metabolites, and the natural productivity of the ecosystem, greatly influenced the nutritional requirements of the juvenile marron under culture.     

Amino acid-chelate: a better source of Zn, Mn and Cu for rainbow trout, Oncorhynchus mykiss

This study aimed to evaluate the amino acid-chelated trace elements as dietary supplement to rainbow trout. Three diets were formulated containing trace elements either from the inorganic salt (SF) or amino acid-chelate (AM). Diets 1 (SF) and 2 (AM) contained the same amount of trace elements from inorganic and amino acid-chelates, respectively. Diet 3 (AM-Hf) was added with trace elements from amino acid-chelatex at one-half of their levels in Diets 1 and 2. Each diet was fed for 15 weeks to three groups of 30 fish each, with an average weight of 1.52±0.21 g. Growth of fish was not affected by the treatment (P>0.05). However, bone (P<0.01) and liver (P<0.05) Cu contents were higher in the AM than the SF group. Similarly, hematocrit level (P<0.05) and alkaline phosphatase (ALP) activity (P<0.01) were higher in the chelate-fed fish. Further, DNA polymerase and CuZnSOD expression in the AM group was highly upregulated (P<0.05) compared to the SF fed fish as quantified by RT-PCR. Absorption and whole body retention of Mn and Zn from the AM were higher (P<0.05) than the inorganic salt. Half supplementation of those fed the elements from AM was at par with the full provision from the inorganic source tested.     

Protein requirement of jundia fingerlings, Rhamdia quelen, at two dietary energy concentrations

A feeding trial was carried out where five protein concentrations [26%, 29%, 33%, 37%, and 41% crude protein (CP)] were fed to jundia fingerlings at two dietary energy concentrations [3200 and 3650 kcal metabolizable energy (ME)/kg diet] to establish the protein requirement for this species. Triplicate groups of 23 fish (average weight 1.52±0.34 g) were each stocked in 120-l aquaria and fed semipurified diets twice a day to apparent satiation. After 90 days, fish weight gain (WG), specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER), energy retention (ER), apparent net protein utilization (ANPU), feed consumption (% body weight) and body composition (crude protein, fat, and ash) were affected by diet composition. Weight gain, SGR, FE, ANPU and ER increased (P<0.05) as the dietary protein concentration increased up to 33% and 37%, for fish fed diets containing 3650 and 3200 kcal, respectively. A significant interaction between dietary protein and energy was observed for WG, SGR, and PER. Feed consumption was not affected by dietary energy concentration, but decreased with increasing dietary protein concentration (P<0.05). Body fat decreased as dietary protein increased at both energy concentrations, but was higher in fish fed the 3650 kcal diet. The opposite was observed for body protein, ER, and ANPU (P<0.05). Our findings demonstrate that jundia presents dietary protein sparing effect when the energy concentration increases from 3200 to 3650 kcal/kg. Jundia protein requirement, determined by the broken line method, is between 32.6% and 37.3% CP, depending on dietary energy concentration.     

Lactic acid fermentation of wheat and barley whole meal flours improves digestibility of nutrients and energy in Atlantic salmon (Salmo salar L.) diets

The effects of lactic acid fermentation of wheat and barley whole meal flours (WMF) on digestibility parameters in Atlantic salmon were studied. The WMFs were inoculated with a specific Lactobacillus strain and fermented for 16 h at 30 °C prior to mixing with other feed ingredients and processing by extrusion. Fermentation of the WMFs significantly decreased total starch (P<0.01) and total mixed-linked (1–3)(1–4)-β-glucan (P<0.001) contents in both cereals. Soluble β-glucans decreased (P<0.001) from 25.2 to 12.0 g kg⁻¹ dry matter in barley WMF during fermentation. In Experiment 1, where diets with 24% untreated wheat or barley WMF and 12%, 24%, or 36% fermented WMFs were fed to Atlantic salmon (0.5 kg) for 25 days, there were indications of improved starch and fat digestibility by fermentation. Experiment 2 comprised diets containing 24% untreated or fermented wheat or barley WMFs fed to each of triplicate groups of Atlantic salmon (0.5 kg) during a 17-day experimental period. This experiment showed that protein (P<0.001), fat (P<0.05) and energy (P<0.001) were more efficiently digested in diets with wheat than in diets with barley. Apparent digestibility of starch was greatly improved by fermentation (P<0.001), more in barley diets (from 47.5% to 67.0%) than in wheat diets (from 51.7% to 65.4%). Improvements in digestibility of fat (P<0.05) and energy (P<0.001) were obtained by fermenting the cereals. The absorption of Na was higher for salmon fed wheat than barley diets (P<0.05). Fermentation resulted in improved Na absorption (P<0.01); from 68.8% to 73.2% for wheat diets and from 60.3% to 71.7% for barley diets. Fermentation caused a significant (P<0.05) improvement in Zn absorption from 32.7% to 40.5% for wheat diets and from 33.2% to 43.5% for barley diets. This may be related to the significant reduction in phytic acid levels seen in both fermented cereals (P<0.001). In conclusion, the potential of wheat and especially barley as ingredients in salmon diets is greatly improved by fermentation.     

Effects of docosahexaenoic, eicosapentaenoic, and arachidonic acids on the early growth, survival, lipid composition and pigmentation of yellowtail flounder (Limanda ferruginea): a live food enrichment experiment

The role of dietary ratios of docosahexaenoic acid (DHA, 22:6n−3), eicosapentaenoic acid (EPA, 20:5n−3) and arachidonic acid (AA, 20:4n−6) on early growth, survival, lipid composition, and pigmentation of yellowtail flounder was studied. Rotifers were enriched with lipid emulsions containing high DHA (43.3% of total fatty acids), DHA+EPA (37.4% and 14.2%, respectively), DHA+AA (36.0% and 8.9%), or a control emulsion containing only olive oil (no DHA, EPA, or AA). Larvae were fed differently enriched rotifers for 4 weeks post-hatch. At week 4, yellowtail larvae fed the high DHA diet were significantly larger (9.7±0.2 mm, P<0.05) and had higher survival (22.1±0.4%), while larvae fed the control diet were significantly smaller (7.3±0.2 mm, P<0.05) and showed lower survival (5.2±1.9%). Larval lipid class and fatty acid profiles differed significantly among treatments with larvae fed high polyunsaturated fatty acid (PUFA) diets having higher relative amounts of triacylglycerols (18–21% of total lipid) than larvae in the control diet (11%). Larval fatty acids reflected dietary levels of DHA, EPA and AA while larvae fed the control diet had reduced amounts of monounsaturated fatty acids (MUFA) and increased levels of PUFA relative to dietary levels. A strong relationship was observed between the DHA/EPA ratio in the diet and larval size (r²=0.75, P=0.005) and survival (r²=0.86, P=0.001). Following metamorphosis, the incidence of malpigmentation was higher in the DHA+AA diet (92%) than in all other treatments (50%). Results suggest that yellowtail larvae require a high level of dietary DHA for maximal growth and survival while diets containing elevated AA exert negative effects on larval pigmentation.     

Effect of supplemental dietary chromium and vanadium on the utilization of different carbohydrates in tilapia, Oreochromis niloticus×O. aureus

Diets containing 40% glucose or starch with either 2 ppm chromium (Cr), 2 ppm vanadium (V) or without either supplement were fed to tilapia, Oreochromis niloticus×O. aureus, to investigate the effect of Cr and V on carbohydrate utilization. Each diet was fed to three aquaria with 18 fish/aquarium in a recirculating, filtered rearing system for 8 weeks. Results indicated that weight gain, protein and energy deposition were significantly (P<0.05) higher in fish fed the starch diet than in those fed the glucose diet. Chromium supplementation significantly increased the weight gain, energy deposition and liver glycogen content in fish fed the glucose diet. Delayed plasma glucose plateau and significantly higher body lipid content were observed in fish fed the glucose diet with Cr than in those without the Cr supplementation.     

Dietary phytase supplementation and the utilisation of phosphorus by Atlantic salmon (Salmo salar L.) fed a canola-meal-based diet

The effect of phytase supplementation to a canola-meal-based diet on phosphorus utilisation in Atlantic salmon was studied in a two-by-two factorial design. Diets were prepared without phytase or inorganic phosphorus supplementation, with phytase, with supplemental inorganic phosphorus and with both phytase and supplemental inorganic phosphorus. Available phosphorus was set below requirement and the total phosphorus set to meet requirements for salmonids. After 12 weeks, there were no significant differences in survival, feed intake and weight gain between diets. There was an interaction effect between supplements on bone ash, bone phosphorus and whole-body phosphorus so that adding phytase, inorganic phosphorus, or both resulted in significantly (P<0.05) higher values for these parameters. An interaction effect was also observed for phosphorus digestibility, phosphorus retention efficiency and phosphorus load. Phosphorus digestibility and retention efficiency were significantly (P<0.05) higher, and phosphorus load was significantly (P<0.05) lower in fish fed the phytase supplemented diet compared with diets containing supplemental inorganic phosphorus. In conclusion, phytase increased phosphorus availability, therefore reducing the need to add inorganic phosphorus and reducing phosphorus waste from plant-meal-based diets for Atlantic salmon.     

Phosphorus requirement of European sea bass (Dicentrarchus labrax L.) juveniles

A growth trial was conducted to estimate the phosphorus requirement of European sea bass juveniles. Six experimental isonitrogenous and isoenergetic semi‐purified diets (casein based) were formulated to contain 0.48%, 0.65%, 0.77%, 0.86%, 1.05% and 1.25% phosphorus (diets D1, D2, D3, D4, D5 and D6 respectively). Dicalcium phosphate was used as dietary phosphorus source. Twelve groups of 25 fish of 10 g initial body weight were allocated to 55‐L tanks in a thermoregulated water recirculating system. Each experimental diet was assigned to duplicate groups of these fish. The trial lasted for 10 weeks and fish were fed two times a day, 6 days a week, to apparent visual satiation. At the end of the trial, final weight of fish fed diet D1 was significantly lower than that of the other groups, except of fish fed diet D4. Mortality of fish fed diet D1 was significantly higher than that of fish fed the other diets, except for diet D6. Feed efficiency and protein efficiency ratios were significantly lower with diet D1 than with the other diets. Nitrogen retention (% nitrogen intake) of fish fed diet D1 was significantly lower than in the other groups, except that of fish fed diet D4. Energy retention (% energy intake) was not significantly different among groups. At the end of the trial there were no differences in whole body composition among groups. Whole body phosphorus content averaged 0.72% (on a fresh weight basis) and was not significantly affected by dietary phosphorus content. Phosphorus retention averaged 6.1 g kg^?1 weight gain and was not significantly different among groups. Phosphorus retention (% phosphorus intake) was significantly higher in fish fed diets D2 and D3 than in fish fed higher dietary phosphorus levels. Expressed per unit body weight per day, phosphorus retention was not significantly different among groups fed diets D2 to D6, while phosphorus losses linearly increased with dietary phosphorus intake. Results of this trial indicate that the phosphorus requirement of sea bass juveniles was satisfied with a diet containing 0.65% of phosphorus.     

Optimum Dietary Level of L-ascorbic Acid for Japanese Eel, Anguilla japonica

A feeding experiment was conducted to determine the optimum dietary level of ascorbic acid (AsA) for Japanese eel juveniles using L-ascorbic acid Ca based on growth, AsA content in tissues, hematology, and bactericidal activity of serum with Escherichia coli . Test diets with six levels of AsA (3, 10, 27,126, 645, and 3,135-mg/kg diet) as Ca ascorbate were fed to juvenile Japanese eels (11.0 ± 0.2 g) once a day for 8 wk. High survival rates (> 80%) were observed among all dietary treatment groups. The specific growth rates of the fish fed diets containing 3 and 10-mg AsA/kg were significantly (P < 0.05) lower than those of other groups. Liver and brain AsA contents of the fish fed diets containing 3, 10, and 27-mg AsA/kg were significantly (P < 0.05) lower than those of the fish fed diets containing 645 and 3,135-mg AsA/kg. Hemoglobin content tended to be higher in the fish fed diets containing 645 and 3,135-mg AsA/kg than those of the fish fed other diets. Hematocrit value and total serum protein content of the fish fed diets containing 645 and 3135 mg AsA/kg were significantly (P < 0.05) higher than those of the other groups. The fish fed diets containing more than 27-mg AsAlkg showed a higher bactericidal activity of serum than the fish fed the diets containing 3-mg and 10-mg AsA/kg. The optimum dietary level of AsA for the Japanese eel juveniles growth was estimated to be more than 27-mg AsA/kg. Furthermore, the inclusion of 645-mg AsA/kg or more also increased the hematocrit, hemoglobin, total serum protein value, and liver and brain vitamin C concentrations.     

Total sulfur amino acid requirement of juvenile hybrid striped bass (Morone chrysops×M. saxatilis)

Two separate feeding trials were conducted to determine the total sulfur amino acid requirement of hybrid striped bass. Semipurified diets containing 35% crude protein from fish muscle and crystalline amino acids were supplemented with graded levels of methionine. Each diet was fed to juvenile fish in triplicate aquaria receiving freshwater for 8 weeks. Fish fed the basal diet which contained 0.38% methionine and 0.13% cystine experienced complete mortality within 1 week. Prior to death, some fish fed inadequate methionine were observed to have bilateral cataracts. Weight gain and feed efficiency of fish were significantly (P<0.01) affected by supplemental methionine. Regression analysis of weight gain data using the broken-line model indicated a total sulfur amino acid requirement (±s.e.) of 1.0% (±0.02%) of dry diet or 2.9% of dietary protein.     

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.     

Vitamin E sparing effect by dietary vitamin C in juvenile hybrid tilapia, Oreochromis niloticus×O. aureus

In order to investigate sparing effects of vitamin C on vitamin E for juvenile hybrid tilapia, fish were fed diets with or without vitamin E each supplemented with either adequate or a high (3× adequate) level of two ascorbate sources, -ascorbic acid (AA) and its derivative, -ascorbyl-2-monophosphate-Mg (C2MP-Mg). Each diet was fed to three replicate groups of fish initially weighing a mean value of 0.54±0.01 g/fish in a closed-recirculated rearing system for 8 weeks. Weight gain and feed efficiency of fish fed the vitamin E-deficient diet supplemented with adequate levels of either AA or C2MP-Mg were significantly lower (P<0.05) than fish fed the other diets. Plasma and liver -tocopherol concentrations were lower in fish fed vitamin E-deficient diets regardless of the level or source of supplemented ascorbate. Gill -tocopherolxxxxxxxx concentration was highest in fish fed vitamin E-adequate diets, intermediate in fish fed vitamin E-deficient diets supplemented with a high level of AA or C2MP-Mg and lowest in fish fed a vitamin E-deficient diet supplemented with an adequate level of AA or C2MP-Mg. Fish fed a vitamin E-deficient diet supplemented with an adequate level of AA or C2MP-Mg had higher hepatic thiobarbituric acid-reactive substances than fish fed the other diets. These data suggest that the high supplementation level (3× adequate) of ascorbate could spare vitamin E in diets for hybrid tilapia and that both AA and C2MP-Mg exhibits the same sparing effect.     

Influence of different dietary amino acid patterns on growth and body composition of juvenile Japanese flounder, Paralichthys olivaceus

A feeding trial using five semi-purified diets (50% crude protein) was conducted to investigate the effects of different dietary amino acid patterns on growth and body composition of juvenile Japanese flounder. The control diet contained casein and gelatin as intact protein sources and four other diets contained 30% casein–gelatin (2:1, w/w) and 20% crystalline amino acids (CAA). CAA were added to the diets to simulate the amino acid pattern found in red sea bream egg protein (REP), Japanese flounder larvae whole body protein (FLP), Japanese flounder juvenile whole body protein (FJP), and brown fish meal protein (BFP), respectively. The test diets were fed to triplicate groups of juveniles (2.75±0.05 g) twice a day for 40 days to evaluate weight gain, survival, feed conversion efficiency (FCE), protein efficiency ratio (PER), and apparent protein utilization (APU). The apparent retention of total dietary amino acids in the whole body and A/E ratios of the whole body were also evaluated. The highest weight gain was observed in fish fed the diet containing the dietary amino acid pattern of BFP followed by fish fed the control, FJP, FLP and the REP diets. Percent survival, FCE, PER and APU were also significantly (P<0.05) affected by the amino acid pattern in the diets, indicating the highest value in fish fed the BFP diet. Except for a few amino acids, the amino acid composition of the whole body did not show marked differences with different dietary amino acid pattern. Results suggest that BFP could be more suitable as a reference amino acid pattern in the diet of juvenile Japanese flounder compared to the amino acid pattern of FLP, FJP or REP.     

Nutrient budgets in tanks with different stocking densities of hybrid tilapia

Nitrogen and phosphorus budgets were estimated in 12 indoor fiberglass tanks stocked with hybrid tilapia (Oreochromis niloticus×O. aureus) at densities of 1 kg, 5 kg, 10 kg and 15 kg/m³ and reared for 14 days. Each density was replicated three times, and the experiment was repeated five times. The water in each tank was changed daily. Fish were fed a 34% protein tilapia feed to satiation twice daily. Feed consumption rate significantly decreased (P<0.05) with increasing density, but the FCR did not vary significantly (P>0.05) among the treatments. The production of one kilogram of fish required 2.0–2.2 kg of feed in different stocking density treatments, while 87.1–95.6 g nitrogen and 12.6–13.8 g phosphorus were released into the water, as metabolic waste. Of the feed input, 21.4% of the nitrogen and 18.8% of the phosphorus were incorporated in the fish harvested.     

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.     

Reduction of stress response in carp,Cyprinus carpioL., held under deteriorating environmental conditions, by oral administration of bovine lactoferrin

Bovine lactoferrin (LF) was evaluated for its ability to suppress stress reactions in carp, Cyprinus carpio L., held under deteriorating environmental conditions. Three test diets containing different levels of LF (0.01, 0.1 and 1%) were fed at 2% of fish body weight per day, i.e. LF at 2, 20 and 200 mg kg(-1) body weight day(-1) was administered orally to carp for 14 days at 20 °C. In the fish reared at a density of 2 individuals 10 l(-1) , plasma cortisol, adrenaline and noradrenaline decreased in the groups fed with 0.1 and 1% LF content diets. In the fish held at a density of 10 individuals 10 l(-1) for 3 days, plasma cortisol, adrenaline, noradrenaline, dopamine and glucose were higher than those at 2 individuals 10 l(-1) in both the control and LF-treated groups. The extent to which these parameters were elevated in the fish held at the same density was reduced with increasing LF content of the diet. Twenty-four hours after exposure to hypoxic conditions (dissolved oxygen level, 2.5 mg l(-1) ), haemoglobin, haematocrit, plasma cortisol, adrenaline, noradrenaline and dopamine increased significantly in all groups. The responses of hypoxic fish fed with 0.1 and 1% LF diets for 14 days were smaller than those of the controls. These results suggest that LF has an ability to reduce the stress response of carp held under deteriorating environmental conditions.     

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.     

Effect of Dietary Lipid Level and Feeding Frequency on the Growth,Feed Utilization,and Body Composition of Juvenile Spotted Seabass,Lateolabrax maculatus

A 6‐wk feeding trial was conducted to evaluate the effects of different dietary lipid levels and feeding frequencies on the growth performance, feed utilization, and body composition of juvenile spotted seabass, Lateolabrax maculatus. Two experimental diets were prepared with two different dietary lipid contents, low lipid (7%; LL) and high lipid (14%; HL). Each diet was fed to triplicate groups of fish (5.5 ± 0.01 g) to apparent satiation at three meals per day, two meals per day, one meal per day, and one meal every 2 d, respectively, for 6 wk. Fish growth performance in terms of weight gain (WG) and specific growth rate (SGR) was significantly affected by frequency of feeding, with increasing values as feeding frequency increased up to twice daily, regardless of dietary lipid content. In addition, fish fed the diet with the HL level (14%) showed significantly higher WG and SGR than those fed the LL diet (7%) at all the feeding frequencies tested. Feed efficiency (FE) and protein efficiency ratio (PER) were affected by both dietary lipid level and feeding frequency. FE and PER values were significantly higher in fish fed the HL diet and/or when fish were fed twice or thrice a day. However, daily feed intake and daily energy intake were significantly affected only by feeding frequency and were significantly reduced when the fish were fed only once every 2 d compared with those fed more frequently. Whole‐body moisture content of fish tended to decrease with increasing dietary lipid level and frequency of feeding. In contrast, whole‐body lipid content increased in fish as dietary lipid level and feeding frequency increased. Consequently, we can conclude that feeding spotted seabass twice daily to apparent satiation is acceptable and sufficient to achieve good growth and FE, as fish performance was not significantly enhanced when feeding was increased from two to three times daily.     

Effects of dietary lipid and environmental salinity on growth,body composition,and cold tolerance of juvenile red drum (Sciaenops ocellatus)

Simultaneous, 6-week feeding trials were conducted in which diets containing menhaden, corn, coconut and hydrogenated menhaden oil at 7.0%, plus a diet containing 14% menhaden oil, were fed to triplicate groups of juvenile red drum (Sciaenops ocellatus) at two different salinities (5 and 32%.). Weight gain was significantly (p < 0.05) affected by diet and salinity. Fish fed the diet containing 14% menhaden oil had the greatest weight gain; whereas, fish fed the diet containing coconut oil gained the least weight. Fish in brackish water had significantly greater weight gain than fish in full-strength seawater over the 6-week period, although fish fed coconut and saturated menhaden oil in brackish water had reduced survival. Dietary lipid also significantly affected muscle and liver total lipid, hepatosomatic index (HSI), and intraperitoneal fat (IPF) ratio, as fish fed the diets containing 14% menhaden oil had higher values for all of these body condition indices.After the feeding trial, fish were subjected to a chronic cold tolerance assay. In the chronic trial, where temperature was gradually reduced over a 3-week period, fish fed the diets containing menhaden oil had significantly lower median lethal temperatures (MLT) than those fish fed the diets containing coconut, corn and saturated menhaden oils. No significant effects of cold exposure were observed on muscle and liver total lipid. Cold exposure prompted a modification in lipid metabolism by lowering total saturated fatty acids and raising (n – 3) highly unsaturated fatty acids (HUFA) in the neutral lipid of liver. Fish with the lowest MLT in the chronic assay exhibited signs of conserving (n – 3) HUFA and depleting (n – 6) fatty acids [primarily 18:2 (n – 6)], resulting in higher (n – 3)/(n – 6) ratios in the polar lipid of liver. These data suggest that the lower lethal temperature of juvenile red drum can be reduced through dietary manipulation involving the inclusion of high levels of dietary lipid rich in (n – 3) HUFA.