Dietary methionine requirement of juvenile blunt snout bream (Megalobrama amblycephala) at a constant dietary cystine level

A 9‐week feeding trial was conducted to investigate the dietary methionine requirement of juvenile Megalobrama amblycephala at a constant dietary cystine level. Six semipurified diets were formulated to contain graded dietary methionine levels from 3.9 to 15.4 g kg^?1 in about 2.5 g kg^?1 increments in the presence of 2.2 g kg^?1 cystine. Results showed that specific growth rate (SGR) and protein efficiency ratio (PER) significantly increased with increasing dietary methionine levels from 3.9 to 12.4 g kg^?1 and thereafter kept stable. Maximum protein productive value (PPV), nitrogen retention efficiency (NRE) and liver weight were observed in 8.5 g methionine kg^?1 diet. Protein contents in whole fish body were positively correlated with dietary methionine level, while lipid contents were negatively correlated with it. Morphological index and hepatic glutamate‐pyruvate transaminase (GPT) activities were independent of dietary methionine levels. However, dietary methionine supplementation significantly improved haematological parameters, plasma methionine and total essential amino acid contents and hepatic glutamate‐oxaloacetate transaminase (GOT) activities. Analysis of dose response using broken‐line regression on the basis of SGR and PPV versus dietary methionine level estimated the optimum dietary methionine requirements of juvenile M. amblycephala to be between 8.5 and 8.4 g kg^?1 of diet (25.0 and 24.7 g kg^?1 of protein) in the presence of 2.2 g kg^?1 cystine, respectively. Hence, the corresponding total sulphur amino acids requirements of this species were calculated to be 10.7 and 10.6 g kg^?1 of diet (31.5 and 31.2 g kg^?1 of dietary protein).     

The effect of dietary methionine on growth,antioxidant capacity,innate immune response and disease resistance of juvenile yellow catfish (Pelteobagrus fulvidraco)

An 11‐week feeding trial was conducted to evaluate the effect of dietary methionine on the growth, antioxidant status, innate immune response and disease resistance to Aeromonas hydrophila of juvenile yellow catfish. Six isonitrogenous and isolipidic practical diets were formulated to contain different graded methionine levels ranging from 6.1 to 16.4 g kg^?1 of dry weight. The results indicated that growth performance and feed utilization were significantly influenced by the dietary methionine levels; fish fed the diet containing 6.1 g kg^?1 methionine level had lower specific growth rate, percentage weight gain (PWG), feed efficiency and protein efficiency ratio than those fed the other diets (P < 0.05). Fish fed the diet containing 16.4 g kg^?1 methionine level had lowest protein contents in whole body and muscle among all treatments. Triacylglycerols, cholesterol, aspartate aminotransferase, alanine aminotransferase and haemoglobin (Hb) in plasma or whole blood were significantly affected by dietary methionine levels. Fish fed the diet containing 6.1 g kg^?1 methionine level had higher superoxide dismutase, glutathione peroxidase activities and malondialdehyde values than those fed other diets. Fish fed diets containing 9.7 and 11.8 g kg^?1 methionine levels had higher lysozyme activity, total immune globulin, phagocytic activity and respiratory burst than those fed other diets. The lowest survival after A. hydrophila challenge was observed in fish fed a diet containing 6.1 g kg^?1 methionine. Quadratic regression analysis of PWG against dietary methionine levels indicated that the optimal dietary methionine requirement for the maximum growth of juvenile yellow catfish was estimated to be 11.5 g kg^?1 of the diet in the presence of 4.0 g kg^?1 cystine (corresponding to 23.5 g kg^?1 of dietary protein on a dry weight basis).     

Partial replacement of fish meal by soybean meal with or without methionine and phytase supplement in diets for juvenile Chinese sucker,Myxocyprinus asiaticus

This study was designed to evaluate the effects of using soybean meal supplemented with or without methionine (M) and graded levels of phytase (P) to replace high‐level (60%) fish meal in the diets for juvenile Chinese sucker. Seven experimental diets (about 430 g kg^?1 crude protein on dry matter basis) were formulated from practical ingredients. The control diet (FM) was formulated to contain 400 g kg^?1 white fish meal (FM), whereas in the other six diets (diets 2–7), soybean meal (SBM) was used to replace 60% fish meal with or without methionine (3 g kg ^?1) and 0,500, 1000, 1500 and 2000 U kg^?1 phytase (designated as SBM, SM, SMP500, SMP1000, SMP1500 and SMP2000, respectively). Results from the feeding trial indicated that SBM without any methionine or phytase supplement replacing about 60% FM significantly affected the growth of fish (P < 0.05). Weight gain of fish fed diet SM was significantly higher than the fish fed diet SBM, but still much lower than fish fed the control diet (P < 0.05). SBM with methionine and phytase supplement significantly improved the growth of fish and apparent digestibility coefficients of phosphorus compared with the groups which fed diet SBM and diet SM (P < 0.05). Weight gain of fish fed SMP1000, SMP1500 and SMP2000 had no significant difference than fish fed control diet. Furthermore, fish fed SMP1500 showed optimum weight gain and ADC of phosphorus between these three groups. This suggested that soybean meal with 3 g kg^?1 methionine and 1500 U kg^?1 phytase supplement could successfully replace 60% fish meal in the diet for juvenile Chinese sucker without affecting growth and enhanced the apparent digestibility coefficient of phosphorus.     

The sparing effect of cystine on methionine at a constant TSAA level in practical diets of juvenile Nile tilapia Oreochromis niloticus

The feeding experiment was conducted to evaluate the replacement effect of cystine on methionine at a constant total sulphur amino acid (TSAA) level in practical diets of juvenile Nile tilapia (Oreochromis niloticus). Soybean meal, cottonseed meal and rapeseed meal were used as the main protein sources in the diets containing 16.4 MJ kg^?1 gross energy and 301 g kg^?1 crude protein. Crystalline DL‐methionine (Met) to L‐cystine (Cys) were supplemented to fulfil various ratios of Met to Cys (60:40, 50:50, 40:60 and 30:70, based on an equimolar sulphur basis; and the analysed ratios were 53:47, 49:51, 34:66 and 31:69). Each diet was fed to triplicate groups of Nile tilapia juveniles (10.1 g mean initial weight) in a recirculation system for 8 weeks. The results showed that the growth performance and nutrient accretion were not affected by dietary methionine:cystine ratios (P > 0.05). However, the survival rates of fish tended to decrease with the decreasing methionine: cystine ratios. The only dietary treatment to achieve 100% survival was the 53:47 methionine: cystine treatment. And methionine digestibility decreased linearly with the decreasing methionine: cystine ratios (P < 0.05). Thus, it was concluded that cystine could replace up to approximately 47% of TSAA requirement on an equimolar sulphur basis without hampering growth performance in the practical diets of juvenile Nile tilapia.     

Dietary arginine requirement of juvenile swimming crab,Portunus trituberculatus

An 8‐week feeding trial was conducted to determine the optimal dietary arginine requirement for juvenile swimming crab Portunus trituberculatus. Six isonitrogenous and isolipidic experimental diets were formulated to contain graded arginine levels which ranged from 15.9 to 33.0 g kg^?1. Each diet was randomly assigned to triplicate groups of 60 juvenile swimming crabs (4.72 ± 0.12 g). The results indicated that dietary arginine had significant effects on weight gain (WG), specific growth rate (SGR), protein productive value, feed efficiency and protein efficiency ratio. Weight gain and SGR significantly increased with the dietary arginine increasing from 15.9 to 27.4 g kg^?1, while with the further increasing from 27.4 to 33.0 g kg^?1, WG and SGR did not increase significantly. Maximum arginine, proline and total essential amino acid contents in muscle were observed in 27.4 g kg^?1 group diet. The swimming crab fed the diet with lower dietary arginine level showed higher AST and lower ALT in the serum. Crab fed with the lower dietary arginine level had significantly lower ALT in the serum than the other groups. Haemolymph indexes were significantly affected by the dietary arginine level except for the cholesterol concentration, and the highest values were all found in 27.4 g kg^?1 group diet. The two slope broken‐line model using SGR showed that the optimal dietary arginine requirement was 27.7 g kg^?1 of the dry matter (56.0 g kg^?1 dietary protein) for juvenile swimming crab.     

The effects of dietary lipid levels on performance and heat‐shock protein response of juvenile white seabass,Atractoscion nobilis

A feeding trial was conducted to study the effect of dietary lipid on growth performance and heat‐shock protein (HSP70 and HSP60) response of white seabass (WSB), Atractoscion nobilis. Five diets were formulated to contain 440 g kg^?1 protein from 300 g kg^?1 fish meal, 240 g kg^?1 soybean meal and 100 g kg^?1 soy protein concentrate with different levels of lipid: 100, 120, 140, 160 or 180 g kg^?1. At the end of the trial, heat shock response based on HSP70 and HSP60 was measured in liver and white muscle from fish at ambient temperature and temperature shock conditions. Final weight and percent gain were significantly higher for fish fed the 100 g kg^?1 lipid diet than for fish fed the rest of the diets (P ≤ 0.05). Feed conversion ratio was lowest for fish fed the 100 g kg^?1 lipid diet. The HSP70 and HSP60 responses were positively correlated to dietary lipid levels following temperature shock. At ambient temperature, HSP60 and HSP70 responses in muscle and HSP60 response in liver increased with dietary lipid level. Temperature shock significantly increased the HSP response of fish in all treatments. Results of this study demonstrated that a moderate (110–120 g kg^?1) level of dietary lipids would be recommended for production diets but a higher dietary lipid level may be required for optimal stress tolerance.     

Effect of dietary l‐methionine concentrations on growth performance,serum immune and antioxidative responses of juvenile Nile tilapia,Oreochromis niloticus

An 8‐week feeding trial was conducted to determine the effect of dietary l ‐methionine supplementation on growth performance, serum immune and antioxidative responses of juvenile Nile tilapia Oreochromis niloticus. Six iso‐nitrogenous (282 g kg^?1 crude protein) diets were formulated to contain graded levels of methionine (0.32%, 0.54%, 0.75%, 0.93%, 1.14% and 1.33% of dry weight) at a constant dietary cysteine level of 0.83 g kg^?1. Each diet was randomly assigned to triplicate groups of 25 juvenile fish (2.3 ± 0.0 g), which were fed three times daily (8:30, 12:30 and 17:00 hours). The results showed that growth performance and feed utilization significantly improved when dietary methionine levels increased (P < 0.05). Using quadratic regression analysis of weight gain against dietary methionine levels indicated that, the optimal dietary methionine requirement for maximum growth of juvenile tilapia was 9.12 g kg^?1 of the dry diet in the presence of 0.83 g kg^?1 cystine. In addition, maximum C4 content and lysozyme activity were observed in fish fed 7.50 g kg^?1 methionine diet; maximum C3 content and superoxide dismutase activity were obtained in fish fed 9.30 g kg^?1 dietary methionine level. While there was no significant difference in serum glutathione peroxidase activity among all methionine supplemented treatments (P > 0.05). Methionine supplementation decreased malondialdehyde content in serum significantly (P < 0.05) when compared with the control diet, while there was no significant difference among supplemented treatments. These data suggested that l ‐methionine affected antioxidant status and promoted serum immune response in juvenile Nile tilapia, and at non‐stressed status, the requirement of dietary methionine in maintaining normal immunity and physiology is lower than that for maximum growth.     

Dietary methionine requirement of juvenile Pseudobagrus ussuriensis

An 8‐week feeding trial was conducted to determine the optimum dietary methionine (Met) requirement of juvenile Pseudobagrus ussuriensis with an initial average weight of 0.60 g reared in indoor flow‐through and aerated aquaria. Six isonitrogenous (430 g kg^?1 protein) and isolipidic (50 g kg^?1 lipid) test diets were formulated to contain graded levels of crystalline L‐methionine (4.9, 9.0, 11.8, 14.2, 18.1 and 20.8 g kg^?1 dry diets, respectively) at a constant dietary cystine level of 2.5 g kg^?1 dry diets. Equal amino acid nitrogen was maintained by replacing methionine with non‐essential amino acid mixture. Fish were randomly allotted to 18 aquaria (1.0 × 0.5 × 0.8 m) with 50 fish to each glass aquarium. Fish were fed twice daily (08:00 and 16:00) to apparent satiation. No significant difference was observed in survival of fish (84.67–91.33%). Specific growth rate (SGR), weight gain (WG), feed conversion ratio (FCR), protein productive value (PPV) and protein efficiency ratio (PER) were significantly affected by different dietary methionine levels (P < 0.05). WG, SGR PPV and PER increased, while FCR decreased with increasing dietary methionine level from 4.9 to 11.8 g kg^?1 (P < 0.05). However, with further increase from 11.8 to 20.8 g kg^?1, WG, SGR PPV and PER significantly decreased, FCR increased (P < 0.05). The whole body and muscle composition were affected by different dietary methionine levels (P < 0.05). Condition factor (CF) increased with increasing dietary methionine levels up to 11.8 g kg^?1 (P < 0.05) and after 11.8 g kg^?1 methionine diet, but not significant, declines were observed (P > 0.05). Hepatosomatic index (HSI) of the 4.9, 9.0, 11.8 and 14.2 g kg^?1 Met diets was significantly higher than that of fish fed diets 18.1 and 20.8 g kg^?1 Met diets (P < 0.05). Viscerosomatic index (VSI) of the 4.9, 9.0 and 11.8 g kg^?1 Met diets was significantly higher than that of fish fed diets 14.2, 18.1 and 20.8 g kg^?1 Met diets (P < 0.05). Quadratic regression analysis of WG and PER against dietary methionine levels indicated that the optimal dietary methionine requirement for maximum growth and feed utilization of juvenile Pseudobagrus ussuriensis was 14.3 and 14.1 g kg^?1 dry diet (35.3 and 34.8 g kg^?1 dietary protein), respectively, in the presence of 2.5 g kg^?1 dry diets cystine.     

Dietary nucleotides improve the growth performance,antioxidative capacity and intestinal morphology of turbot (Scophthalmus maximus)

A growth trial was conducted to evaluate the effects and safety of nucleotides in low fish meal diets on the growth performance, antioxidative capacity and intestinal morphology of turbot (Scophthalmus maximus). High fish meal control diet was formulated with 500 g kg^?1 fish meal. Seven levels (0.075, 0.15, 0.225, 0.300, 1.5 and 3.0 g kg^?1, respectively) of nucleotides were added to a low fish meal basal diet, which was formulated with 400 g kg^?1 fish meal. The eight experimental diets were fed to groups of juvenile turbot (initial weight: 6.0 ± 0.03 g) for 60 days. Results showed that compared with high fish meal control diet, low fish meal basal diet treatment had lower total antioxidative capacity (T‐AOC), glutathione peroxidase activity, fold height of proximal and distal intestine, enterocyte height of all evaluated enteric section and microvillus height of mid‐intestine and distal intestine (P < 0.05). However, supplemented nucleotides in diets could significantly improve growth (specific growth rate, SGR), feed utilization, antioxidative capacity and intestinal morphology of turbot (P < 0.05). Broken‐line regression analysis of SGR and T‐AOC showed that the optimal supplemental levels of dietary nucleotide for juvenile turbot were 0.366 and 0.188 g kg^?1, respectively. In summary, 0.300 g kg^?1 of dietary nucleotides was helpful in improving growth, feed utilization, antioxidative capacity and intestinal morphology of turbot fed with low fish meal diet. Excessive dietary nucleotides (3.0 g kg^?1) might cause oxidative stress and morphological damage in intestine and then reduce the growth of turbot.     

The effect of dietary methionine concentrations on growth performance of juvenile Nile tilapia (Oreochromis niloticus) fed diets with two different digestible energy levels

A growth trial was conducted to examine the effect of dietary digestible energy (DE) content on methionine (Met) utilization and requirement in juvenile Nile tilapia (Oreochromis niloticus). Ten iso‐nitrogenous (288 g kg^?1 protein) practical diets, with two DE levels (10.9 MJ kg^?1; 12.4 MJ kg^?1) and five methionine supplementation levels (0, 1, 2, 4 and 6 g kg^?1), were hand‐fed twice daily to triplicate groups of Nile tilapia (initial body weight 8.95 ± 0.06 g) for 8 weeks. Weight gain (WG) and specific growth rate (SGR) increased significantly with increasing dietary methionine concentration at the same DE content (P < 0.001). At the same dietary methionine level, WG and SGR of fish fed high‐DE diets were significantly higher than that of fish fed low‐DE diets (P = 0.0001), although no interaction was found between dietary DE and methionine supplementation. Based on quadratic regression analysis between dietary methionine concentration and weight gain, optimal methionine requirement for maximum growth, expressed as g Met required kg^?1 diet (low‐ versus high‐DE diets), increased as diet DE concentration increased (7.34 versus 9.90 g kg^?1 diet, respectively; with cysteine 4.70 g kg^?1 diet). The results indicated that diet DE content affects methionine utilization and requirement in juvenile Nile tilapia, fish fed high‐DE diets required more methionine for maximum growth.     

Effect of dietary protein reduction with lysine and methionnine supplementation on growth performance,body composition and total ammonia nitrogen excretion of juvenile grass carp,Ctenopharyngodon idella

A 63‐day growth trial was undertaken to estimate the effects of supplemented lysine and methionine with different dietary protein levels on growth performance and feed utilization in Grass Carp (Ctenopharyngodon idella). Six plant‐based practical diets were prepared, and 32CP, 30CP and 28CP diets were formulated to contain 320 g kg^?1, 300 g kg^?1 and 280 g kg^?1 crude protein without lysine and methionine supplementation. In the supplementary group, lysine and methionine were added to formulate 32AA, 30AA and 28AA diets with 320 g kg^?1, 300 g kg^?1 and 280 g kg^?1 dietary crude protein, respectively, according to the whole body amino acid composition of Grass Carp. In the groups without lysine and methionine supplementation, weight gain (WG, %) and specific growth rate (SGR, % day^?1) of the fish fed 32CP diet were significantly higher than that of fish fed 30CP and 28CP diets, but no significant differences were found between 30CP‐ and 28CP‐diet treatments. WG and SGR of the fish fed 32AA and 30AA diets were significantly higher than that of fish fed 28AA diets, and the performance of grass carp was also significantly improved when fed diets with lysine and methionine supplementation (P < 0.05), and the interaction between dietary protein level and amino acid supplementation was noted between WG and SGR (P < 0.05). Feed intake (FI) was significantly increased with the increase in dietary protein level and the supplementation of lysine and methionine (P < 0.05), but feed conversion ratio (FCR) showed a significant decreasing trend (P < 0.05). Two days after total ammonia nitrogen (TAN) concentration test, the values of TAN discharged by the fish 8 h after feeding were 207.1, 187.5, 170.6, 157.3, 141.3 and 128.9 mg kg^?1 body weight for fish fed 32CP, 32AA, 30CP, 30AA, 28CP and 28AA diets, respectively. TAN excretion by grass carp was reduced in plant‐based practical diets with the increase in dietary protein level and the supplementation of lysine and methionine (P < 0.05). The results indicated that lysine and methionine supplementation to the plant protein sources‐based practical diets can improve growth performance and feed utilization of grass carp, and the dietary crude protein can be reduced from 320 g kg^?1 to 300 g kg^?1 through balancing amino acids profile. The positive effect was not observed at 280 g kg^?1 crude protein level.     

Effects of partial substitution of dietary fish meal by fermented soybean meal on growth performance,amino acid and biochemical parameters of juvenile black sea bream Acanthopagrus schlegeli

A feeding trial was conducted to evaluate the effect of replacing fish meal protein with fermented soybean meal (FSM) on the growth performance, feed utilization, amino acid profile, body composition, morphological parameters, activity of antioxidant and digestive enzymes of black sea bream (Acanthopagrus schlegeli) juvenile. Five isonitrogenic and isolipidic diets were prepared with levels of 0 (control), 80, 160, 240 and 320 g kg^?1 FSM. Triplicate groups (40 fish per tank) of juvenile black sea bream with initial weight of 1.17 ± 0.04 g were hand‐fed to visual satiation at three meals per day for 8 weeks. The fish fed diets containing different levels of FSM had no significant differences regarding survival and specific growth rate compared with control group. Feed and protein efficiency ratios of fish fed diet containing 320 g kg^?1 FSM were significantly lower than those of control group. Daily feed intake and daily protein intake of fish fed diet containing 240–320 g kg^?1 were significantly higher than those of control group. Hepatosomatic index and condition factor of fish were not affected by different dietary FSM level. Fish fed diets containing 240–320 g kg^?1 FSM had significantly higher visceral somatic index than control group. Whole body proximate and amino acid compositions of fish were not affected by dietary FSM level. The activity of digestive enzymes in the intestine was not affected by dietary FSM level. The activity of glutathione peroxidase in liver was significantly higher for fish fed the diet containing 160 g kg^?1 FSM compared with control group. This study showed that up to 40% fish meal in the diets of juvenile black sea bream could be replaced by fermented soybean meal with supplementation of methionine, lysine and taurine.     

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

The experiment was conducted to determine the leucine requirement of juvenile Pacific white shrimp Litopenaeus vannamei (Boone) in low‐salinity water (0.50–1.20 g L^?1). Six diets were formulated to contain 410 g kg^?1 crude protein with fish meal, peanut meal and precoated crystalline amino acids with different concentration of l ‐leucine (16.72, 19.60, 22.06, 24.79, 27.28 and 30.16 g kg^?1 dry diet). Each diet was randomly assigned to triplicate groups of 30 shrimps (0.38 ± 0.002 g), and the feed trial lasted for 8 weeks. The results indicated that the maximum weight gain was observed at 24.95 g kg^?1 dietary leucine group, whereas the diets containing higher leucine concentration conversely reduced the growth performance (P < 0.05). Moreover, the highest body protein content and body protein deposition and the lowest haemolymph AST and ALT activities were also found at 24.95 g kg^?1 dietary leucine group. With the increase in leucine in diets, a dose‐dependent increase was found in body lipid content and haemolymph urea concentration. The polynomial regression calculated using weight gain, feed efficiency and body protein deposition indicated that the optimal dietary leucine requirement for L. vannamei reared in low‐salinity water was 23.73 g kg^?1 leucine of dry diet, correspondingly 57.88 g kg^?1 of dietary protein.     

Effects of dietary protein and lipid levels on growth,feed utilization and body composition in Pseudobagrus ussuriensis fingerlings

An 8‐week feeding trial was conducted to investigate the optimum dietary protein and lipid levels for growth, feed utilization and body composition of Pseudobagrus ussuriensis fingerlings (initial weight: 3.40 ± 0.01 g). Twelve diets containing four protein levels (350, 400, 450 and 500 g kg^?1 crude protein) and three lipid levels (50, 100 and 150 g kg^?1 crude lipid) were formulated. Fish were randomly allotted to 36 aquaria (1.0 × 0.5 × 0.8 m) with 25 fish to each glass aquarium. Fish were fed twice daily (08:00 and 16:00) to apparent satiation. The results showed that weight gain and specific growth rate (SGR) decreased with increasing dietary lipid level from 50 to 150 g kg^?1 at the same dietary protein level. Fish fed the diets containing 150 g kg^?1 lipid exhibited higher feed conversion ratio (P < 0.05), lower protein efficiency ratio (PER) and nitrogen retention efficiency (NRE) relative to fish fed the diet containing 50 and 100 g kg^?1 lipid. Weight gain and SGR significantly increased with increasing dietary protein from 350 to 450 g kg^?1 at the same dietary lipid level, and even a little decline in growth with the further increase in dietary protein to 500 g kg^?1. Daily feed intake, NRE and PER were significantly affected by both dietary protein and lipid levels (P < 0.05) and tended to decrease with increasing dietary protein and lipid levels. Whole‐body protein content increased as protein levels increased and lipid levels decreased. Whole‐body lipid and muscle lipid content increased with increasing dietary lipid level, and decreased with increasing dietary protein at each lipid level. There was no significant difference in condition factor and viscerosomatic index among fish fed the diets. Hepatosomatic index was affected by dietary lipid level (P < 0.05), and increased with increasing dietary lipid level at the same protein level. These results suggest that the diet containing 450 g kg^?1 protein and 50 g kg^?1 lipid with a P/E ratio of 29.1 mg protein kJ^?1 is optimal for growth and feed utilization of P. ussuriensis fingerlings under the experimental conditions used in the study.     

Effects of DL‐methionine supplementation on the success of fish meal replacement by plant proteins in practical diets for juvenile gibel carp (Carassius auratus gibelio)

A ten‐week feeding trail was conducted to investigate the effects of increasing DL‐methionine (Met) supplementation on the success of fish meal (FM) replacement with plant proteins in practical diets for juvenile gibel carp, Carassius auratus gibelio. Twelve isoenergetic diets were formulated including two 150 g kg^?1 FM diets (Diet 1—positive control 1 reflecting a commercial diet and Diet 2—positive control 2 reflecting a commercial diet but with balanced essential amino acid (EAA) profile) and ten 50 g kg^?1 FM diets (negative controls) supplemented with graded levels (0–3.0 g kg^?1) of DL‐Met (Diets 3–12). Each diet was fed to triplicate groups of gibel carp, near satiation four times daily for 10 weeks. Diet 2 with balanced EAA profile produced better final weight, specific growth rate (SGR) and feed conversion ratio (FCR) than the negative control diet containing no supplemental Met (Diet 3), but did not significantly differ from Diet 1. However, DL‐Met supplementation (0.5–3.0 g kg^?1) in the negative control diets (Diets 4–12) produced growth performances similar to those fed the positive control diets (Diets 1 and 2). Based on quadratic regression analysis, the optimal dietary Met level with 5.2 g kg^?1 of dietary cysteine (Cys) was found to be 7.1 g kg^?1 dry diet for SGR and FCR. The corresponding total sulphur amino acid requirements (Met + Cys) of this species were calculated to be 12.3 g kg^?1 dry diet for SGR and FCR. DL‐Met supplementation in 50 g kg^?1 FM diets showed a decreasing trend in plasma cholesterol contents (p < .05). No significant differences were observed in whole‐body composition, plasma protein, triglyceride and free EAA contents among dietary treatments, while plasma aspartate transaminase, albumin and ammonia contents were significantly influenced by dietary Met levels. Juvenile gibel carp grew equally well on 150 g kg^?1 FM diet or 50 g kg^?1 FM diets balanced for EAA profile with supplemental amino acids. The results of this study overall indicate that balancing dietary amino acid levels with DL‐Met supplementation is a key strategy in successfully reducing FM levels in the diets of gibel carp.     

Evaluation of dietary inclusion of housefly maggot (Musca domestica) meal on growth,fillet composition and physiological responses for barramundi,Lates calcarifer

The study was to evaluate the effects of dietary fish meal (FM) partially replaced by housefly maggot meal (HMM) on growth, fillet composition and physiological responses of juvenile barramundi, Lates calcarifera. HMM at 100, 150, 200 and 300 g kg^?1 was supplemented in the basal diet to replace dietary FM protein. Basal diet without HMM supplementation was used as control. Total of five experimental diets were fed to triplicate groups of juvenile barramundi (initial weight: 9.66 ± 0.22 g) in a flow‐through rearing system for 8 weeks. Fish fed all experimental diets showed no effects (P > 0.05) on weight gain and whole body protein, lipid and moisture content. Fish fed control diet and 100 g kg^?1 HMM diet had the highest (P < 0.05) hepatic superoxide dismutase (SOD) activity, followed by 150 g kg^?1 HMM group, the lowest in 200 and 200 g kg^?1 HMM groups. Hepatic thiobarbituric acid reactive substance (TBARS) value was the highest in fish fed 150–300 g kg^?1 HMM diets, followed by 100 g kg^?1 HMM group and the lowest in fish fed the control diet. Fish fed the 300 g kg^?1 HMM diet had lower plasma lysozyme activity than fish fed other diets. The results indicated that up to 300 g kg^?1 HMM can be used to substitute dietary FM protein without negative effect on growth. Although physiological responses were also considered, up to 100 g kg^?1 HMM in barramundi diet was recommended.     

Dietary thiamin and pyridoxine requirements of fingerling Indian major carp,Cirrhinus mrigala (Hamilton)

Two experiments were conducted to quantify the dietary thiamin (experiment I) and pyridoxine (experiment II) requirements of fingerling Cirrhinus mrigala for 16 weeks. In experiment I, dietary thiamin requirement was determined by feeding seven casein–gelatin‐based diets (400 g kg^?1 CP; 18.69 kJ g^?1 GE) with graded levels of thiamin (0, 0.5, 1, 2, 4, 8 and 16 mg kg^?1 diet) to triplicate groups of fish (6.15 ± 0.37 cm; 1.89 ± 0.12 g). Fish fed diet with 2 mg kg^?1 thiamin had highest specific growth rate (SGR), protein retention (PR), RNA/DNA ratio, haemoglobin (Hb), haematocrit (Hct), RBCs and best feed conversion ratio (FCR). However, highest liver thiamin concentration was recorded in fish fed 4 mg thiamin kg^?1 diet. Broken‐line analysis of SGR, PR and liver thiamin concentrations exhibited the thiamin requirement in the range of 1.79–3.34 mg kg^?1 diet (0.096–0.179 μg thiamin kJ^?1 gross energy). In experiment II, six casein–gelatin‐based diets (400 g kg^?1 CP; 18.69 kJ g^?1 GE) containing graded levels of pyridoxine (0, 2, 4, 6, 8 and 10 mg kg^?1 diet) were fed to triplicate groups of fish (6.35 ± 0.37 cm; 1.97 ± 0.12 g). Fish fed diet containing 6 mg kg^?1 pyridoxine showed best SGR, FCR, PR, RNA/DNA ratio, Hb, Hct and RBCs, whereas maximum liver pyridoxine concentration was recorded in fish fed 8 mg kg^?1 dietary pyridoxine. Broken‐line analysis of SGR, PR and liver pyridoxine concentrations reflected the pyridoxine requirement from 5.63 to 8.61 mg kg^?1 diet. Data generated during this study would be useful in formulating thiamin‐ and pyridoxine‐balanced feeds for the intensive culture of this fish.     

Dietary leucine requirement of Juvenile Nile tilapia,Oreochromis niloticus

An 8‐week feeding trial was conducted to evaluate the effects of dietary leucine on growth performance, feed utilization, body composition and non‐specific immune responses of juvenile Nile tilapia. Five isonitrogenous and isoenergetic diets were formulated to contain graded levels of L‐leucine (5.3, 8.1, 10.9, 13.2, 15.6 and 18.1 g kg^?1 diet, respectively) from dietary ingredients and crystalline L‐leucine. Each diet was randomly assigned to triplicate groups of 20 juvenile fish (1.94 ± 0.01 g) three times daily to apparent satiation. Results showed that the weight gain (WG) and specific growth rate (SGR) increased as dietary leucine concentrations increased from 5.3 to 13.2 g kg^?1 and then decreased slightly with further increase in dietary leucine concentrations. Quadratic regression analysis (y = ?522.6x² + 1304.x + 132.6, R² = 0.684) on weight gain against dietary leucine levels indicated that the optimal dietary leucine requirement was estimated to be 12.5 g kg^?1 diet (corresponding to 43.1 g kg^?1 of dietary protein). Leucine supplementation had no impact on the survival and body composition of tilapia. Serum lysozyme activity of fish fed diet containing 13.2 g kg^?1 leucine significantly increased compared to fish fed diet containing 5.3 g kg^?1. Serum superoxide dismutase activity and immunoglobulin M (IgM) concentration were not significantly affected by dietary leucine supplementation.     

Replacement of dietary fish meal by soybean meal supplemented with crystalline methionine for Japanese seabass (Lateolabrax japonicus)

Two 8‐week feeding trials were conducted to evaluate soybean meal (SBM) as a fish meal substitute in diets for Japanese seabass, Lateolabrax japonicas. In trial I, a control diet (C) contained 400 g kg^?1 fish meal, and 20%, 40%, 60% and 80% of the fish meal were replaced with SBM, supplied with 3 g kg^?1 DL‐methionine and 2 g kg^?1 L‐lysine (S20, S40, S60 and S80). In trial II, 60% and 80% of the fish meal in diet C were replaced with SBM, supplied with DL‐methionine at 3 g kg^?1 (S60, S80) or 6 to 7 g kg^?1 (RS60, RS80). The feed intake was lower in fish fed diet C than in fish fed diets S20, S40, S60 and S80 (trial I). No significant differences were found in the weight gain, nitrogen retention efficiency and body composition between fish fed diets C, S20, S40 and S60 (trial I), between fish fed diets S60 and RS60 or between fish fed diets S80 and RS80 (trial II). This study indicates that dietary fish meal level for Japanese seabass can be reduced to 160 g kg^?1 by using SBM as a fish meal substitute.     

Total aromatic amino acid requirement of juvenile grass carp (Ctenopharyngodon idella)

This experiment was conducted to investigate total aromatic amino acid requirement of juvenile grass carp Ctenopharyngodon idella. Six isonitrogenous and isoenergetic semipurified diets containing casein and gelatin with graded level of phenylalanine (7.8, 11.1, 14.4, 17.6, 21.7, 24.9 g kg^?1 DM) were formulated. Each diet was randomly assigned to triplicate group of 30 fish (3.58 ± 0.002 g, mean ± SEM) each tank for 8 weeks. The highest weight gain (WG, %), final body weight (g) and specific growth rate were recorded when phenylalanine level was 17.6 g kg^?1 of the diet. Fish muscle protein content, protein efficiency ratio (PER), feed conversion ratio and alanine aminotransferase were significantly affected by dietary phenylalanine level. The polynomial regression calculated using WG and PER indicated that the optimal dietary total aromatic amino acid (phenylalanine + tyrosine) requirement for juvenile grass carp was 24.4 g kg^?1 of the diet, corresponding to 65.9 g kg^?1 of dietary protein.