The influence of dietary phospholipid level on the performances of juvenile amberjack, Seriola dumerili, fed non-fishmeal diets

The objective of the present study was to investigate the effect of dietary phospholipid (PL) level on growth and feed intake of juvenile amberjack ( Seriola dumerili ) fed non-fishmeal (non-FM) diet containing alternative protein sources; soybean protein isolate, tuna muscle by-product powder and krill meal. Three non-FM diets were prepared to contain three levels (14, 37 and 54 g kg⁻¹ dry diet) of PL (soybean lecithin acetone insoluble, 886 g kg⁻¹) and growth performance was monitored in a 30-day growth trial by using 2.6 g of fish. The results indicated that final body weight, weight gain and feed intake significantly increased with increasing dietary PL level. At the highest dietary PL level (54 g kg⁻¹ dry diet), the fish consumed 14.8% and 10.2% as much feed as those fish fed diets containing 14 g kg⁻¹ dry diet and 37 g kg⁻¹ dry diet PL, respectively. An increasing tendency with increasing dietary PL level on feed efficiency was observed. In conclusion, the present study demonstrated that dietary PL supplementation could increase feed intake, and improve the growth of juvenile S. dumerili fed non-FM diets. Therefore, purified PL might be a good candidate to stimulate the growth of fish through enhancing the feed intake when they are fed diets containing alternative protein sources.     

The effect of phytase on apparent digestibility of four practical plant feedstuffs fed to striped bass, Morone saxatilis

This study was conducted to determine the effect of phytase on apparent dry matter (DM), crude protein and phosphorus (P) digestibility of four plant feedstuffs (isolated soya protein, ISP; soyabean meal, SBM; corn gluten meal, CGM and wheat middlings, WM) fed to striped bass Morone saxatilis . One reference diet was formulated based solely on animal feed ingredients. Four test diets were prepared by mixing 60–75% of the reference diet with 40–25% of the test ingredient in order to reach similar levels of total P (0.67–0.73%) and to have a minimum of 35% protein (36.1–53.0%). Chromic oxide was added at 0.5% of the diet and used as an indigestible marker. A phytase solution was sprayed postpelleting on the test diets at a concentration of 1000 phytase units kg⁻¹ (PU kg⁻¹) dry diet. The test diets (with or without phytase supplementation) and the reference diet (nine treatments total) were fed to 3-year-old striped bass and were replicated in time ( n =3) during the 4-week period. Digestibility of DM was significantly lower ( P  < 0.001) for SBM and WM when compared with CGM and ISP and was not influenced by phytase supplementation. Crude protein digestibility was also not affected by phytase supplementation and was significantly lower ( P  < 0.09) for SBM when compared with ISP. Phosphorus digestibility was improved by approximately 23% with the addition of phytase for all four feedstuffs tested ( P  < 0.001). Furthermore, WM had significantly lower ( P  < 0.0001) P digestibility when compared with the other feedstuffs, irrespective of phytase supplementation.     

Effects of dietary protein to metabolizable energy ratios and total protein concentrations on the performance of yellow perch Perca flavescens

Juvenile yellow perch Perca flavescens were fed semipurified diets with varying protein to metabolizable energy ratios (PME, g protein MJ⁻¹ metabolizable energy) and nutrient densities in three experiments to determine recommended dietary protein and energy concentrations. Experiment 1 fish (18.6 g) were fed diets containing 450 g crude protein kg⁻¹ dry diet and 14.5–18.8 MJ ME kg⁻¹ dry diet for 10 weeks. No differences were found in the growth of experiment 1 fish fed the different diets. Experiment 2 fish (21.9 g) were fed diets containing 15.7 MJ ME kg⁻¹ dry diet and 210–420 g crude protein kg⁻¹ dry diet for 8 weeks. Fish fed the diet containing 340 g kg⁻¹ protein (diet PME = 22) exhibited the greatest weight gain. Experiment 3 fish (27.1 g) were fed diets with a PME of 22 and varying nutrient density (yielding 205–380 g crude protein kg⁻¹ dry diet) for 8 weeks. No differences were found in the growth of experiment 3 fish. Yellow perch fed the semipurified diets exhibited increased liver fat content, liver size and degree of liver discoloration compared with fish fed a commercial fish meal-based diet. Liver changes may have resulted from high dietary carbohydrate levels. We conclude that a protein level of 210–270 g kg⁻¹ dry diet is suitable for juvenile yellow perch provided that the dietary amino acid profile and carbohydrate content are appropriate for yellow perch.     

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

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

Effects of dietary phosphorus level on non-faecal phosphorus excretion from yellowtail (Seriola quinqueradiata Temminck & Schlegel) fed purified and practical diets

Non-faecal phosphorus (P) was determined for large yellowtail to estimate a minimum available P requirement (Experiment  1) and to justify inorganic P supplementation in a fish meal-based diet (Experiment 2). In Experiment 1, purified diets with incremental P concentrations were fed to yellowtail (mean weight 917 g) at a feeding rate of 1.5% of body weight. The peaks of non-faecal P excretion appeared 5–6 h after feeding in fish fed more than 4.5 g available P kg⁻¹ dry diet. Broken-line analysis indicated that the minimum available P requirement was 4.4 g kg⁻¹ dry diet. In Experiment 2, a purified diet (PR) containing 6.5 g available P kg⁻¹ and a fish meal-based diet with (F1) and without (F0) additional phosphorus were fed to yellowtail (mean weight 1.1 kg) at 1.5% (PR) and 2% (F0 and F1) feeding rates respectively. There was no significant difference in P excretion between fish fed the F0 (5.5 g soluble P kg⁻¹ dry diet) and the PR diet. However, significantly higher (34.5%) amounts of non-faecal P excretions (7.4 g soluble P kg⁻¹ dry diet) were found in fish fed F1 compared with the F0 diet. This suggested that there was an excess of dietary P in the F1 diet and that supplementation is not needed in fish meal-based diets for large yellowtail.     

Effect of fermentation on the nutritive value of sesame seed meal in the diets for rohu, Labeo rohita (Hamilton), fingerlings

Six isonitrogenous (350 g kg⁻¹ crude protein) and isoenergetic (17573 kJ kg⁻¹) experimental diets incorporating raw and fermented sesame ( Seasamum indicum ) seed meal at 200, 300, and 400 g kg⁻¹ into a fishmeal based diet were fed to rohu Labeo rohita fingerlings for 60 days and the growth performance and feed utilization efficiency of the fish was studied. The antinutritional factor phytic acid, from raw sesame seed meal, could be reduced below detection limit by fermentation with lactic acid bacteria ( Lactobacillus acidophilus ). Fermentation of the oilseed meal resulted in reduction of the tannin content from 20 to 10 g kg⁻¹. In terms of growth response, feed conversion ratio and protein efficiency ratio, a diet containing 400 g kg⁻¹ fermented sesame seed meal resulted in a significantly ( P  < 0.01) best fish performance. In general, growth and feed utilization efficiencies of fish fed fermented sesame seed meal diets were superior to those fed raw oilseed meal diets. Apparent protein digestibility (APD) values decreased with increasing levels of raw oilseed meal. APD was, however, significantly ( P  < 0.01) higher at all levels of incorporation of fermented sesame seed meal, while diets containing raw oilseed meal resulted in poor protein and lipid digestibility. Carcass protein and lipid contents of fish fed fermented sesame seed meal diets increased with increasing level of incorporation, being highest with 400 g kg⁻¹ fermented oilseed meal-containing diet. The results showed that sesame seed meal may be incorporated in carp diets up to 200 g kg⁻¹ and 400 g kg⁻¹ in raw and treated (fermented) forms respectively.     

Quantitative dietary threonine requirement of juvenile Pacific white shrimp, Litopenaeus vannamei (Boone) reared in low-salinity water

An 8-week feeding trial was conducted to determine the threonine requirement of juvenile Pacific white shrimp Litopenaeus vannamei (Boone) in low-salinity water (0.50–1.50 g L⁻¹). Diets 1–6 were formulated to contain 360 g kg⁻¹ crude protein with fish meal, wheat gluten and pre-coated crystalline amino acids with six graded levels of l -threonine (9.9–19.0 g kg⁻¹ dry diet). Diet 7, which was served as a reference, contained only intact proteins (fish meal and wheat gluten). Each diet was randomly assigned to triplicate groups of 30 shrimps (0.48±0.01 g), each four times daily. Shrimps fed the reference diet had similar growth performance and feed utilization efficiency compared with shrimps fed the diets containing 13.3 g kg⁻¹ or higher threonine. Maximum specific growth rate (SGR) and protein efficiency ratio were obtained at 14.6 g kg⁻¹ dietary threonine, and increasing threonine beyond this level did not result in a better performance. Body compositions, triacyglycerol and total protein concentrations in haemolymph were significantly affected by the threonine level; however, the threonine contents in muscle, aspartate aminotransferase and alanine aminotransferase activities in haemolymph were not influenced by the dietary threonine levels. Broken-line regression analysis on SGR indicated that optimal dietary threonine requirement for L. vannamei was 13.6 g kg⁻¹ dry diet (37.8 g kg⁻¹ dietary protein).     

Effects on growth and feed utilization of Chinese longsnout catfish Leiocassis longirostris Günther of replacement of dietary fishmeal by soybean cake

Four practical diets containing different levels of soybean cake (0, 155, 320, 490 g kg⁻¹) were prepared to investigate the effect of replacement of fishmeal by soybean cake on the Chinese longsnout catfish ( Leiocassis longirostris Günther) during a 62-day growth trial. The diets were isonitrogenous, isoenergetic and contained about 430 g kg⁻¹ crude protein and 20 MJ kg⁻¹ gross energy. With increasing levels of dietary soybean cake, growth rate and feed utilization decreased; feeding rate and the contents of dry matter, fat and energy of fish body were not significantly affected while body protein showed lowest value in the fish fed the diet containing 320 g kg⁻¹ soybean cake.     

Use of full-fat winged bean Psophocarpus tetragonolobus seed meal as a protein feedstuff in fish-meal free diets for African catfish Clarias gariepinus

Mature winged bean Psophocarpus tetragonolobus seeds were quick-cooked and the full-fat meal derived was used to completely replace menhaden fish meal as a dietary protein source for the African catfish Clarias gariepinus . Five dry practical diets (400 g crude protein kg⁻¹ and 17.5 kJ gross energy g⁻¹ dry diet) containing menhaden fish meal (diet 1) or winged bean meal with or without graded levels of supplemental L -methionine (diets 2, 3, 4 and 5; 0, 5, 10 and 15 g kg⁻¹, respectively) were fed to catfish fingerlings (5.8  +  1.2 g) for 70 days. Weight gain, growth rate, feed conversion and protein utilization by catfish fed a winged bean meal diet without L -methionine supplementation (diet 2) was inferior ( P  > 0.05) to that in catfish fed the other diets, where performance differed nonsignificantly. Carcass protein of catfish was lower ( P  < 0.05) while liver protein was higher ( P  < 0.05) in catfish fed the winged bean meal diet without methionine supplementation. Results suggest that winged bean meal cannot replace fish meal as a protein source in catfish diets except with a minimum supplementation with 5 g L -methionine kg⁻¹ diet.     

Bioavailability of feed grade calcium phosphate incorporated into practical diets for Penaeus vannamei

Practical diets designed for penaeid shrimp are commonly supplemented with phosphorus, which may lead to unnecessary nutrient loading of the culture system and effluent waters as well as unnecessary investments in a nutrient that is not utilized by the culture species. To facilitate the optimization of phosphorus levels in practical shrimp feeds, research was conducted with Penaeus vannamei juveniles to determine the biological availability of two feed-grade calcium phosphate sources. A practical basal diet containing 350 g protein kg⁻¹ diet and 9.8 g P kg⁻¹ diet was formulated using anchovy and soybean meal as the primary protein and phosphorus sources. The basal diet was supplemented with graded levels of phosphorus and offered to juvenile shrimp (0.57 ± 0.017 g) over a 10-week period. Weight gain and estimated feed efficiency values increased with phosphorus supplements, indicating a dietary deficiency of the basal diet. Under the reported conditions, a dietary supplement of 1.4 or 2.3 g P kg⁻¹ diet was required for maximum growth and estimated feed efficiency values if Cefkaphos (primarily monobasic calcium phosphate) or Dynafos (primarily dibasic calcium phosphate) was utilized. Dynafos was determined to have a relative biological value (RBV) of 63.8% of Cefkaphos based on final weights of the shrimp offered diets containing 1.25 g supplemental P kg⁻¹ diet. A similar RBV of 60.9% was estimated based on broken-line analyses of growth data. There were no significant differences in apparent net phosphorus retention (ANPR) for the basal diet (23.1%) or diets supplemented with 1.25 g P kg⁻¹ diet originating from Cefkaphos (25.7%) or Dynafos (17.9%). However, shifts in ANPR values of the diets corresponded to biological availability of the two phosphorus sources.     

Optimum dietary soybean meal level for maximizing growth and nutrient utilization of on-growing gilthead sea bream (Sparus aurata)

Six isonitrogenous [450 g kg⁻¹ crude protein (CP)] and isoenergetic diets (23 kJ g⁻¹) with six levels of defatted soybean meal inclusion (0, 132, 263, 395, 526 and 658 g kg⁻¹) in substitution of fish meal were evaluated in gilthead sea bream of 242 g initial weight for 134 days. Fish fed diets S0, S13, S26 and S39 had a similar live weight (422, 422, 438 and 422 g, respectively) but fish fed diets S53 and S66 obtained the lowest final weight (385 and 333g, respectively), and similar results were presented in specific growth rate (SGR). Fish fed diets S53 and S66 also obtained the highest feed conversion ratio (FCR). Quadratic multiple regression equations were developed for SGR and FCR which were closely related to dietary soybean level. The optimum dietary soybean levels were 205 g kg⁻¹ for maximum SGR and 10 g kg⁻¹ for minimum FCR. Sensorial differences were appreciated by judges between fish fed S0 and S39 soybean level, but after a re-feeding period of 28 days with diet S0, these differences disappeared.     

Effect of methionine on intestinal enzymes activities, microflora and humoral immune of juvenile Jian carp (cyprinus carpio var. Jian)

An 8-week feeding experiment was conducted to determine the effect of dietary methionine supplementation on intestinal microflora and humoral immune of juvenile Jian carp (initial weight of 9.9 ± 0.0 g) reared in indoor flow-through and aerated aquaria. Eight amino acid test diets (350 g kg⁻¹ crude protein, CP), using fish meal, soybean-condensed protein and gelatin as intact protein sources supplemented with crystalline amino acids, were formulated to contain graded levels of methionine (0.6–22.0%) at a constant dietary cystine level of 3 g kg⁻¹. Each diet was randomly assigned to three aquaria. Growth performance and feed utilization were significantly influenced by the dietary methionine levels ( P  < 0.05). Maximum weight gain, feed intake occurred at 12 g kg⁻¹ dietary methionine ( P  < 0.05). Methionine supplementation improved hepatopancreas and intestine weight, hepatosomatic and intestine index, intestinal γ-glutamyltransferase and creatine kinase activity, Lactobacillus count, Bacillus count, lysozyme activities, lectin potency, sim-immunoglobulin M content, addiment C3,C4 contents and serum total iron-binding capacity and declined Escherichia coli and Aeromonas counts. Quadratic regression analysis of weight gain against dietary methionine levels indicated that the optimal dietary methionine requirement for maximum growth of juvenile Jian carp is 12 g kg⁻¹ of the dry diet in the presence of 3 g kg⁻¹ cystine.     

Dietary phosphorus requirement of juvenile Atlantic salmon, Salmo salar L.

The objective of this study was to determine the dietary phosphorus (P) requirement of juvenile Atlantic salmon, Salmon salar L. Triplicate groups of fish (mean initial weight 1.4 g) were fed semipurified, casein-gelatine-based diets containing one of five levels of P (4, 8, 10, 15 and 25 g kg⁻¹) from Ca(H₂PO₄)₂·H₂O, or a commercial feed (17 g kg⁻¹ P) for 9 weeks. Weight gains did not differ significantly among treatment groups fed the experimental diets but were slightly less than gains in fish fed the commercial feed. Feed efficiency (wet weight gain/dry feed consumed) was similar in all groups, averaging 1.45. Availability of dietary P, estimated from apparent retention and apparent digestibility, was 86%. Whole-body P concentrations declined in fish fed diets containing less than 10 g kg⁻¹ P. Fitting a logistic curve to dietary P vs. whole-body P concentrations indicated that a minimum of 11 g kg⁻¹ dietary P (9 g kg⁻¹ digestible P) was required by juvenile Atlantic salmon to maintain whole-body P concentrations at initial levels. Calculation of a dietary requirement using a simple factorial model which incorporated measurements of P availability, feed efficiency and normal whole-body P concentration indicated that the dietary requirement was approximately 10 g kg⁻¹. The dietary requirement established in this study (10–11 g kg⁻¹) is higher than previously reported for Atlantic salmon or other fishes. Possible reasons for the wide range of reported dietary P requirements in fishes are discussed.     

Dietary microbial phytase increased the phosphorus digestibility in juvenile Korean rockfish Sebastes schlegeli fed diets containing soybean meal

This study was conducted to evaluate the effects of dietary microbial phytase supplementation on nutrient digestibility, growth performance and body composition in juvenile Korean rockfish fed soybean meal-based diets.Nine experimental diets were formulated to be isonitrogenous and isocaloric to contain 48.6% crude protein (CP) and 15.9 kJ of available energy/g with or without dietary phytase (Natuphos-5000™, BASF, NJ, USA) supplementation. White fish meal (FM) provided 89.1% of the total protein in the basal diet (S₀), in the other eight diets, 30 or 40% FM protein was replaced by soybean meal: 70% FM+30% soybean meal (S₃₀); 70% FM+30% 1000 U phytase pretreated SM (S₃₀PP₁₀₀₀); 70% FM+30% SM+1000 U phytase/kg diet (S₃₀P₁₀₀₀); 70% FM+30% SM+2000 U phytase/kg diet (S₃₀P₂₀₀₀); 60% FM+40% SM (S₄₀); 60% FM+40% 1000 U P_tre SM (S₄₀PP₁₀₀₀); 60% FM+40% SM+1000 U phytase/kg diet (S₄₀P₁₀₀₀); and 60% FM+40% SM+2000 U phytase/kg diet (S₄₀P₂₀₀₀). After 2 weeks of the adaptation, triplicate groups of 20 fish initially averaging 7.25±0.04 g (mean±S.D.) were randomly distributed into the aquarium and were fed one of the experimental diets for 8 weeks.By the end of the 8-week feeding trial, supplementation of phytase significantly improved the apparent digestibility coefficient (ADC) of phosphorus in rockfish diets (P<0.05) containing 30% and 40% soybean meal regardless of the level and method of phytase supplementation. Supplementation of phytase significantly increased the ADC of dry matter in diets containing 30% soybean meal (P<0.05). However, phytase had no influence on growth performance and whole body composition of fish. The pretreatment of soybean meal with 1000 U phytase improved weight gain (WG) when 30% fish meal protein was replaced by soybean meal. Based on the experimental results, we conclude that supplementation of phytase can improve the apparent digestibility coefficient of phosphorus in Korean rockfish.     

Effects of digestible protein levels in isonitrogenous diets on growth performance and tissue composition of juvenile Atractoscion nobilis

A study was undertaken to estimate the effects of isonitrogenous diets (ca. 604 g kg⁻¹ crude protein) containing formaldehyde-treated (FT) fish meal and graded levels of digestible protein (DP) (541, 491, 372, 347 and 247 g kg⁻¹) on growth performance and tissue composition of juveniles white seabass. Five diets were formulated to contain increasing levels of FT fish meal (from 0 to 384 g kg⁻¹) and decreasing levels of non-treated fish meal (from 480 to 96 g kg⁻¹). Each dietary treatment was fed in triplicate to apparent satiation to groups of 25 fish for 50 days. Significantly higher growth performance and feed conversion ratio were obtained in fish-fed diets containing 491 or 541 g kg⁻¹ DP, compared with all other treatments. Apparent digestibility coefficient of protein in the diets was not significantly affected by the inclusion of treated fish meal in the diets. Estimation of protein requirements using a broken-line regression analysis indicated that maximum weight gain would be obtained with a diet containing 503 ± 23 g kg⁻¹ DP. The results from this study suggest that a single-diet formulation using protein treated with formaldehyde as filler might be useful to estimate the requirement of DP for fish.     

Nutritional evaluation of waste date fruit as partial substitute for soybean meal in practical diets of juvenile Nile tilapia, Oreochromis niloticus L.

The potential of waste date meal (WDM; low-quality date palm, Phoenix dactylifera L.) as a carbohydrate source in formulated diets for Nile tilapia was evaluated. Four isocaloric-practical diets (15.7 kJ g⁻¹) were formulated incorporating WDM at 0, 100, 200 and 300 g kg⁻¹ levels as partial substitutes for soybean meal (SBM). These were designated D₀ [284 g crude protein (CP) and 383 g carbohydrate (CHO) kg⁻¹ diet], D₁ (279 g CP and 446 g CHO kg⁻¹ diet), D₂ (207 g CP and 495 g CHO kg⁻¹ diet) and D₃ (175 g CP and 578 g CHO kg⁻¹ diet). Each diet was fed to three replicate groups of 30 fish [20.20 ± 0.09 g (±SE)] for 75 days. No feed-related mortality was observed during the entire experimental period. Final body weight (FBW) and specific growth rate (SGR) in the different treatments were statistically not significantly different ( P  > 0.05). Protein efficiency rate (PER) was lowest in diet D₀ and increased with decrease of SBM content (D₁–D₃). A significant increase in whole body lipid content was recorded in fish fed diets D₂ and D₃. Results showed that WDM could be a substitute for SBM up to 300 g kg⁻¹ in practical Nile tilapia diets without compromising growth.     

Supplementing copper to a fish meal based diet fed to Atlantic salmon parr affects liver copper and selenium concentrations

The present experiment was conducted to study growth and tissue responses in Atlantic salmon, Salmo salar L., fed a fish meal based diet supplemented with copper (Cu). The findings of the experiment were used to evaluate the need for dietary Cu supplementation. Atlantic salmon parr, initially weighing ≊ 7.5 g, were randomly distributed among 10 tanks, with 300 fish in each tank. Duplicate groups of fish were fed a fish meal based diet containing 3.5 mg Cu kg⁻¹, or this diet supplemented with 5, 10, 50 or 100 mg Cu kg⁻¹ (as CuSO₄*5 H₂O) for 12 weeks. Growth was recorded and blood haemoglobin measured. The Cu concentrations in whole body, liver, serum and selected muscle samples were measured, as was liver selenium (Se) concentration.
There were no difference in growth among the dietary treatments. There were, however, significant differences among the dietary groups in liver Cu and Se concentrations. The fish fed the diet supplemented with 5 mg Cu kg⁻¹ had increased liver Cu concentration compared with the other groups. Similar trends were found for serum Cu concentration and whole-body Cu concentration, but these effects were not significant. Liver Cu and Se concentrations were positively correlated and liver Se concentrations were inversely correlated to dietary Cu concentration, confirming an interaction between these two elements in salmon.
There may be a positive effect of a modest Cu supplementation level, and we suggest that a small amount of Cu (5–10 mg kg⁻¹) should be added to fish meal based diets.     

Effect of dietary lipid level on muscle composition in Atlantic salmon Salmo salar

This study was conducted to determine the effects of feeding increasing lipid concentrations (310, 380 and 470 g kg^–1 lipid on dry weight) in diets based mainly on herring byproducts to Atlantic salmon Salmo salar . The diets were isonitrogenous, varying in dietary lipid content at the expense dietary starch. Average fish weight increased from 1.2 kg in April to 2.2–2.7 kg at the end of the feeding trial in September. Significantly greater growth was found in fish fed either the 380 g kg⁻¹ or the 470 g kg⁻¹ lipid diets compared with the 310 g kg⁻¹ lipid diet. Muscle lipid content increased in all dietary groups on a wet weight basis from 7.7 ± 1.4% to 12 ± 3% in salmon fed the 310 g kg⁻¹ lipid diet, and to 16 ± 2% in salmon fed the 380 g kg⁻¹ and 470 g kg⁻¹ lipid diets. In fish of similar weight there was a positive correlation between dietary lipid and muscle lipid concentrations. Low concentrations of muscle glycogen were detected in fish fed each of the diets, while muscle vitamin E concentrations slowly decreased as muscle lipid increased. Muscle fatty acid composition reflected dietary fatty acid profiles, containing similar percentages of total saturated, monoenic and n-3 fatty acids (20:5n-3 and 22:6n-3) in fish from all dietary treatment groups. However, a higher ratio of n-3/n-6 was found in muscle from fish fed the 470 g kg⁻¹ lipid diet compared with the other two groups. Blood chemistry values varied somewhat, but all values were within normal ranges for Atlantic salmon of these sizes.     

Full-fat soybean meal in diets for Atlantic halibut: growth, metabolism and intestinal histology

Isonitrogenous and isocaloric diets containing 0, 18 or 36% toasted full-fat soybean meal (FFSM) were fed to Atlantic halibut. The diets were fed to five tanks of fish each for 34 days (period 1). Four tanks from each treatment were then retained in the growth experiment for a further 32 days (period 2), while the groups of fish from one tank from each of the 0 and 36% FFSM groups were split and transferred to two metabolism tanks each. The initial weight of the fish in the growth trial was 169 ± 1 g (mean ± SEM, n =12; weight range 89–253 g) and the final weight was 317 ± 5 g. There was no significant effect of dietary treatment on specific growth rate (range, 0.8–1.1% day⁻¹), feed consumption (0.5–0.7% body weight day⁻¹), feed efficiency (1.3–1.6 g wet gain g dry feed⁻¹), protein retention (48–55%) or energy retention (49–57%). The fat, protein and energy concentrations in the fish increased during the trial and were not affected by the diet. The hepatosomatic index in fish fed with 36% FFSM diet was significantly lower (1.7%) than in the other groups (2.2%) ( P  < 0.05). No differences in intestinal morphology were observed between dietary treatments and no pathological reactions were identified in any of the samples. In the metabolism trial, there were no significant differences in oxygen consumption or ammonia excretion between fish fed with 0 and 36% FFSM diets. In conclusion, up to 36% FFSM may be added to diets for Atlantic halibut without negative effects on growth, feed efficiency or intestinal morphology.     

Dietary vitamin E requirement of hybrid striped bass (Morone chrysops female × M. saxatilis male)

This study was conducted to determine the dietary vitamin E requirement of juvenile hybrid striped bass ( Morone chrysops female ×  Morone saxatilis male). Semi-purified diets supplemented with 0.2 mg Se kg⁻¹ from Na₂SeO₃ and either 0 (basal), 10, 20, 40, 60, or 80 mg vitamin E kg⁻¹ as  DL -α-tocopheryl acetate were fed to hybrid striped bass initially averaging 1.8 ± 0.1 g (mean ± SD) for 12 weeks. Fish fed the basal diet, which contained 5.8 mg α-tocopherol kg⁻¹ dry weight, were darker in colour and had reduced weight gain, as well as generally reduced haematocrit values compared with fish fed diets supplemented with vitamin E. In addition, fish fed diets containing less than 20 mg supplemental vitamin E kg⁻¹ had significantly ( P  < 0.05) reduced weight gain and feed efficiency compared with those fed diets supplemented with vitamin E at 20–80 mg kg⁻¹. Dietary supplementation of vitamin E caused incremental increases in the concentration of α-tocopherol in both plasma and liver tissues. However, hybrid striped bass fed graded levels of vitamin E did not exhibit a dose response in terms of ascorbic acid-stimulated lipid peroxidation of hepatic microsomes. Regression analysis of weight gain data using the broken-line model indicated a minimum vitamin E requirement ( ±  SE) of 28 ( ±  3) mg kg⁻¹ dry diet. Based on these data, the dietary vitamin E requirement of hybrid striped bass appears to be similar to that determined for other fish species.