Optimal dietary methionine requirement of juvenile Chinese sucker,Myxocyprinus asiaticus

A total of 630 juvenile Chinese sucker, with an average initial weight of 1.72 ± 0.05 g, were fed seven diets for 56 days to study the effect of dietary methionine levels on growth, feed utilization, body composition and haematological parameters on juvenile Chinese sucker. Diet 1 using fish meal as the sole protein source and diets 2–7 using fish meal and fermented soybean meal as intact protein sources supplemented with crystalline amino acids contained six levels of l ‐methionine ranging from 6.4 to 18.9 g kg^?1 of dry diet at a constant dietary cystine level of 3.7 g kg^?1. Each diet was randomly assigned to three aquaria. Results indicated that the highest weight gain, specific growth rate (SGR), feed efficiency ratio, protein efficiency ratio and protein productive value occurred at 13.9 g methionine kg^?1 diet among the methionine supplemented dietary groups, beyond which they showed declining tendency. The whole body and muscle protein contents of juvenile Chinese sucker were positively correlated with dietary methionine level, while muscle lipid content was negatively correlated with it. The total essential amino acids content of muscle was increased significantly with increasing dietary methionine level from 6.4 to 13.9 g kg^?1 (P < 0.05). Apparent digestibility coefficients of dietary protein were significantly affected by dietary treatments. Serum protein, cholesterol and triacylglycerol increased with increasing dietary methionine levels, but showed a relatively lower value for fish fed the 18.9 g methionine kg^?1 diet. Quadratic regression analysis of SGR against dietary methionine level indicated that optimal dietary methionine requirement for juvenile Chinese sucker was 14.1 g kg^?1 of the diet in the presence of 3.7 g kg^?1 cystine (corresponding to 32.0 g kg^?1 of dietary protein on a dry‐weight basis).     

Dietary thiamin could improve growth performance,feed utilization and non‐specific immune response for juvenile Pacific white shrimp (Litopenaeus vannamei)

This study evaluated the effect of dietary thiamin on growth performance, feed utilization and non‐specific immune response for juvenile Pacific white shrimp, Litopenaeus vannamei. Six isonitrogenous and isolipidic practical diets were formulated with graded thiamin levels of 6.9, 32.7, 54.2, 78.1, 145.1 and 301.5 mg kg^?1 of dry diet, respectively. Each diet was randomly assigned to triplicate groups of 30 juvenile shrimp and provided four times each day to apparent satiation. Weight gain (WG) and specific growth rate (SGR) of the shrimp were significantly influenced by the dietary thiamin levels, the maximal WG and SGR occurred at 54.2 mg kg^?1 dietary thiamin level. However, with further increase in dietary thiamin level from 54.2 to 301.5 mg kg^?1, the WG and SGR significantly decreased. Shrimp fed the 54.2 mg kg^?1 thiamin diet exhibited higher feed efficiency, protein efficiency ratio and protein productive value than those fed the other diets. Dry matter and protein content in whole body were significantly affected by the dietary thiamin levels. Thiamin concentration in hepatopancreas significantly increased when the dietary thiamin level increased from 6.9 to 145.1 mg kg^?1. The total protein, glucose, triacylglycerol and cholesterol contents in hemolymph were not significantly affected by the dietary thiamin levels. Dietary thiamin had significantly influenced superoxide dismutase, catalase and lysozyme activities in hemolymph. Results of this study indicated that the optimal dietary thiamin requirements estimated using a two‐slope broken‐line model based on WG and thiamin concentration in hepatopancreas were 44.66 and 152.83 mg kg^?1, respectively.     

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.     

Comparative studies on dietary protein requirements of juvenile and on‐growing gibel carp (Carassius auratus gibelio) based on fishmeal‐free diets

Two trials were conducted to investigate protein requirements of juvenile (3.18 g in Trial 1) and on‐growing (87.1 g in Trial 2) gibel carp, Carassius auratus gibelio var. CAS III. Six isoenergetic diets containing 250–500 g kg^?1 dietary protein were formulated using soy protein concentrate (SPC) and casein as protein sources. The results showed that weight gain (WG) increased when dietary protein increased from 250 to 400 g kg^?1 and decreased at 400 to 500 g kg^?1 CP in Trial 1, while WG increased when dietary protein increased from 250 to 350 g kg^?1 and kept constant at 350 to 500 g kg^?1 CP in Trial 2. With increasing dietary protein, feed conversion ratio (FCR) decreased, while protein retention efficiency (PRE) decreased in Trial 1 and was not affected in Trial 2. Apparent digestibility coefficient of protein (ADC_p) increased with increasing dietary protein in two trails. Trypsin activity increased with dietary protein in the juveniles and was not affected in on‐growing fish. Hepatic alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities increased with dietary protein. Broken‐line and quadratic regression of WG estimated that dietary protein requirements for maximum growth were about 402–427 g kg^?1 for the juvenile and 337–418 g kg^?1 for on‐growing gibel carp.     

Dietary niacin levels in practical diets for Litopenaeus vannamei to support maximum growth

This study investigated the effects of dietary niacin on growth performance, feed utilization and non‐specific immune response in juvenile Pacific white shrimp. Six isonitrogenous and isolipidic practical diets were formulated with graded niacin levels of 10.9, 65.8, 121.2, 203.4, 387.5 and 769.3 mg kg^?1 of dry diet, respectively. Results indicated that per cent weight gain (WG), specific growth rate (SGR), feed efficiency (FE), protein efficiency ratio (PER) and protein productive value (PPV) were significantly influenced by the dietary niacin levels. The maximum WG and SGR occurred at 121.2 mg kg^?1 niacin diet. However, survival and proximate composition of whole body were not significantly affected by the dietary niacin levels. Dietary niacin levels had no significant effects on the total protein, glucose, triacylglycerol and cholesterol contents in the haemolymph. The activity of catalase and lysozyme in the haemolymph was significantly affected by dietary niacin levels. Based on a two‐slope regression analysis of SGR against dietary niacin level, the dietary niacin requirement of juvenile Pacific white shrimp was 109.6 mg kg^?1.     

Dietary isoleucine requirement of juvenile blunt snout bream,Megalobrama amblycephala

A 9‐week feeding trial was conducted to estimate the dietary isoleucine requirement of juvenile blunt snout bream. Six isonitrogenous and isoenergetic experimental diets were formulated to contain graded isoleucine levels ranging from 5.3 to 20.1 g kg^?1 dry diet. At the end of the experiment, weight gain (WG), specific growth rate (SGR), feed efficiency ratio (FER) and protein efficiency ratio (PER) increased with increasing dietary isoleucine level up to 11.1 g kg^?1 dry diet, and dietary isoleucine level above 14.2 g kg^?1 dry diet declined these performances. Dietary isoleucine levels (14.2 and 17.3 g kg^?1 dry diet) significantly improved whole‐body protein content, but decreased whole‐body lipid, plasma triglyceride and cholesterol contents. Significantly lower visceral fat index (VFI) in fish fed with 14.2 g kg^?1 dietary isoleucine was observed compared to those fed with deficient or excessive isoleucine. Dietary isoleucine supplementation significantly increased plasma isoleucine concentration, while plasma valine and leucine concentrations showed a reversed trend. Dietary isoleucine levels regulated the target of rapamycin (TOR) gene expression and improved plasma superoxide dismutase (SOD) activity in juvenile blunt snout bream. Based on second‐order polynomial regression model analysis of SGR and FER, the optimum dietary isoleucine requirement was estimated to be 13.8 g kg^?1 dry diet (40.6 g kg^?1 dietary protein) and 14.0 g kg^?1 dry diet (41.2 g kg^?1 dietary protein), respectively.     

Effects of dietary aflatoxin B1 on growth performance,body composition,haematological parameters and histopathology of juvenile Pacific white shrimp (Litopenaeus vannamei)

An 8‐week feeding trial was conducted to evaluate the effects of dietary aflatoxin B₁ (AFB₁) on growth performance, haematological parameters and histological changes in juvenile Pacific white shrimp, Litopenaeus vannamei. Six practical diets (455 g kg^‐1 protein, 78 g kg^‐1 lipid) with different levels of AFB₁ (0, 25, 50, 100, 500, 1000 μg kg^?1) were formulated. Each diet was fed to triplicate groups of shrimps (initial weight: 0.52 g). The results showed that shrimp fed with control diet (0 μg kg^?1 AFB₁) had significant higher weight gain (WG) and specific growth rate (SGR) than other groups. However, there were no significant differences in feed efficiency (FE) or hepatosomatic index (HSI) among all groups. Compared to the control diet, AFB₁ supplementation significantly changed the activities of shrimp serum alanine aminotransferase (ALT), aspartate aminotransferase (AST), total antioxidant capacity (T‐AOC) and glutathione S‐transferase (GST) and the content of cholesterol (CHO). Histological damages were identified in the hepatopancreas of shrimp when dietary AFB₁ level was over 107.6 μg kg^?1. Based on this study, it was concluded that the AFB₁ level in Pacific white shrimp diet should be <38.1 μg kg^?1.     

Dietary arginine requirement of juvenile grass carp Ctenopharyngodon idella (Valenciennes in Cuvier & Valenciennes, 1844)

This experiment was conducted to estimate the optimum requirement of arginine for juvenile grass carp Ctenopharyngodon idella. Six isonitrogenous (38%) and isoenergetics (16 MJ kg^?1) semi‐purified diets containing casein and gelatine with graded level of arginine (0.93, 1.20, 1.51, 1.84, 2.10 and 2.41 g 100 g^?1 DM) were formulated. Each diet was randomly assigned to triplicate groups of 25 fish each tank (initial weight: 3.84 ± 0.01) for 10 weeks. The highest weight gain (WG, %) was recorded when arginine level was 2.10% of the diet. Dietary arginine level higher than 1.84% significantly increased the protein contents of whole body. Whole body amino acid composition of juvenile grass carp was not significantly affected by the dietary arginine level. Plasma‐free arginine level was increased linearly with increasing of arginine level in the diets, and the plasma‐free ornithine level was significantly higher when the dietary arginine level was 2.41% compared with other groups. Quadratic model analysis of SGR data indicated that the minimum recommended dietary arginine requirement for grass carp was 2.17% of the diet, corresponding to 5.71% of dietary protein.     

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.     

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.     

Effects of extruded and pelleted diets with differing lipid levels on growth,nutrient retention and serum biochemical indices of tilapia (Oreochromis aureus × Tilapia nilotica)

This study was conducted to evaluate the effects of extruded diets and pelleted diets with varying dietary lipid levels on growth performance and nutrient utilization of tilapia. Six diets, containing three levels of lipid at 40, 60 or 80 g kg^?1 (with the supplemental lipid of 0, 20 or 40 g kg^?1, respectively), were prepared by extruding or pelleting and then fed to tilapia juveniles (8.0 ± 0.1 g) in cages (in indoor pools) for 8 weeks. The results indicated that the fish that were fed the diet with 60 g kg^?1 of lipid had a higher weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER), lipid retention (LRE), energy retention (ERE), apparent protein digestibility, apparent dry matter digestibility and a lower feed conversion ratio (FCR) than those fed the diet with 40 g kg^?1 lipid in both the extruded diet and pelleted diet (P < 0.05). As the dietary lipid level increased from 60 to 80 g kg^?1, these parameters were not further improved, even digestibilities of the crude protein and dry matter decreased (P < 0.05). With the dietary lipid level increased, whole‐body lipid content significantly increased (P < 0.05), serum aspartate aminotransferase, alkaline phosphatase, total cholesterol and low‐density lipoprotein cholesterol (LDL‐C) tended to increase (P > 0.05), whereas whole‐body protein content, serum triglyceride (TG), high‐density lipoprotein cholesterol (HDL‐C) and HDL‐C/LDL‐C tended to decrease (P > 0.05). Fish fed with the extruded diets had a higher WG, SGR, hepatosomatic index (HSI), PER, protein retention (PRE), LRE, ERE, TG, apparent digestibility of protein and dry matter, as well as a lower FCR, than those fed with the pelleted diets at the same dietary lipid level (P < 0.05). These results suggested that tilapia fed with the extruded diets had a better growth and higher nutrient utilization than fish fed with the pelleted diets, when dietary lipid level ranged from 40 to 80 g kg^?1 and at dietary crude protein level was 280 g kg^?1. The optimum dietary lipid level was 60 g kg^?1 in both the pelleted and extruded diets, and extrusion did not affect dietary lipid requirement of the tilapia.     

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).     

Effects of dietary arginine on growth performance,feed utilization,haematological parameters and non‐specific immune responses of juvenile Nile tilapia (Oreochromis niloticus L.)

An 8‐week feeding trial was conducted to evaluate the effects of dietary arginine on growth performance, feed utilization, haematological parameters and non‐specific immune responses of juvenile Nile tilapia (6.03 g). Five isonitrogenous and isoenergetic diets were formulated to contain graded levels of L‐arginine (8.5 g kg^?1, 11.5 kg^?1, 15.3 kg^?1, 18.8 kg^?1 and 22.4 kg^?1 dry diet) from dietary ingredients and crystalline arginine. Each diet was randomly assigned to triplicate groups of 25 juvenile fish (6.04 ± 0.02 g) three times daily (8:30, 12:30, and 17:00 hours) to apparent satiation. Results showed that the weight gain (WG) and special growth rate (SGR) increased with increasing dietary arginine levels up to 15.3 kg^?1 and remained nearly the same thereafter. Arginine supplementation had no impact on the survival, body composition and haematological parameters of tilapia. However, the immune responses (plasma nitric oxide content, total nitric oxide synthase (T‐NOS) and lysozyme activity) significantly (P < 0.05) increased with increasing dietary argentine level after stress. Quadratic regression analysis (y = ?0.7147x² + 25.986x + 147.53 R² = 0.8736) on weight gain against dietary arginine levels indicated that the optimal dietary arginine requirement was estimated to be 18.2 kg^?1 of the diet (corresponding to 6.24% of dietary protein on a dry weight basis). The present study indicates that arginine has an immunostimulatory potential to help juvenile Nile tilapia cope with stress conditions such as Streptococcus iniae infection.     

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).     

Effects of dietary microbial levan on growth performance,RNA/DNA ratio and some physio‐biochemical responses of Labeo rohita (Hamilton) juveniles

Six isonitrogenous and isocaloric semi‐purified diets were prepared with different levels of microbial levan: control (Basal), T1 (Basal + 2.5 g kg^?1 diet), T2 (Basal + 5 g kg^?1 diet), T3 (Basal + 7.5 g kg^?1 diet), T4 (Basal + 10 g kg^?1 diet) and T5 (Basal + 12.5 g kg^?1 diet), fed to six groups of fish in triplicate tanks. The results of the 60 days feeding trail showed that supplementation of dietary levan significantly affected the weight gain percentage and specific growth rate of the treatment groups fed at 10 g kg^?1 or more levan. Lowest feed conversion ratio (FCR) value and highest survival percentage among levan fed groups were observed with 12.5 g kg^?1 incorporation (T5) and was comparable with (T4) group. Significant increase in muscle RNA level and RNA/DNA ratio was observed with the increasing dietary levan. Fish fed 12.5 g kg^?1 levan had significantly higher protease, amylase and lipase activities compare with the control group. Lowest Aspartate aminotransferase (AST) activity in the liver and muscle was observed in the T5 group fed with highest level of dietary levan. Overall results conclude that dietary microbial levan incorporation at 12.5 g kg^?1 could be used as potent dietary prebiotic for the culture of L. rohita juveniles.     

Effects of dietary phosphorus and starch levels on growth performance,body composition and nutrient utilization of grass carp (Ctenopharyngodon idella Val.)

Six iso‐nitrogenous (410 g kg^?1) diets with three levels of total phosphorus (P4, P10 and P18 g kg^?1) and two levels of starch (S200 and S350 g kg^?1) were fed to triplicate groups of 30 fish to evaluate whether the high level of dietary phosphorus could improve the utilization of starch. Over 8‐week‐growth trial, best weight gain (WG) and specific growth rate (SGR) (P < 0.05) were observed in fish fed the P10/S200 and P18/S200 diets. WG and SGR significantly decreased as starch levels increased whereas for P4, while lipid contents of liver and whole body, hepatosomatic index and intraperitoneal fat ratio (IPF) significantly increased. These results suggested that high dietary starch will depress the growth performance and cause lipid accumulation. Within both starch levels, fish fed diet with P4 tended to produce lower (P < 0.05) WG and SGR, and had higher (P < 0.05) values of IPF. The whole body lipid, ash, calcium, phosphorus and iron contents were significantly affected by dietary phosphorus levels. Supplied phosphorus could improve the growth and decrease the whole body lipid, but there is no more effect after the phosphorus requirement was met at 10 g kg^?1.     

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.     

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.     

Effects of cholesterol on growth,feed utilization,body composition and immune parameters in juvenile oriental river prawn,Macrobrachium nipponense (De Haan)

An 8‐week feeding trial was conducted to investigate the effects of dietary cholesterol levels on growth, feed utilization, body composition and immune parameters in juvenile oriental river prawn, Macrobrachium nipponense. Six isolipid (80 g kg^?1 crude lipid) and isoproteic (400 g kg^?1 crude protein) diets, supplemented with 0, 3.0, 6.0, 9.0, 12.0 and 15.0 g kg^?1 cholesterol, were evaluated. Growth performance and feed utilization of M. nipponense were improved as dietary cholesterol levels increased. Weight gain and specific growth rate were highest, and feed conversation ratio was lowest, when prawns were fed a diet supplemented with 9.0 g kg^?1 cholesterol. However, final body weights and survival rates of juvenile M. nipponense were not affected significantly by dietary cholesterol. Body composition of prawns, including moisture, crude protein and crude lipid, was not significantly affected by changes in dietary cholesterol. The immune parameters measured in hepatopancreas, including total antioxidant capacity, and glutathione, catalase, alkaline phosphatase and acid phosphatase activities, were at optimum levels in prawns fed with 9.0 g kg^?1 dietary cholesterol. In summary, the best growth performance, lowest feed conversation ratio, and the most enhanced antioxidant capacity and immunity parameters were attained in juvenile M. nipponense when fed a diet supplemented with 9.0 g kg^?1 cholesterol.     

Growth,feed utilization and body composition of juvenile golden pompano Trachinotus ovatus fed at different dietary protein and lipid levels

A feeding trial was conducted to determine the suitable dietary protein and lipid levels for juvenile golden pompano Trachinotus ovatus reared in net pens. Ten test diets were formulated at five levels of crude protein (330, 370, 410, 450 or 490 g kg^?1) and two levels of crude lipid (65 or 125 g kg^?1). Golden pompano fingerlings (initial body weight 4.7 g ind^?1) were fed the test diets for 8 weeks. Weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), nitrogen retention efficiency (NRE), energy retention efficiency (ERE), condition factor (CF), hepatosomatic index (HSI), body protein content and total nitrogen waste (TNW) were dependent on both dietary protein and lipid levels. Feed intake (FI) and viscersomatic index (VSI) were dependent on dietary protein level, while body lipid content was dependent on dietary lipid level. Weight gain increased with increasing the dietary protein level (at the same lipid level) but was lower at the dietary lipid level of 65 g kg^?1 than at 125 g kg^?1 (at the same protein level). Fish fed at the dietary protein levels of 460–490 g kg^?1 had higher WG and lower FCR than at 330–410 g kg^?1. Energy retention efficiency tended to increase with increasing the dietary protein level from 330 to 410 g kg^?1, while no significant difference was found in nitrogen retention efficiency between the dietary protein levels (at the same lipid level). Results of this study suggest increasing the dietary lipid level from 65 to 125 g kg^?1 could not induce protein‐sparing action in golden pompano, and the suitable dietary protein and lipid levels for juvenile golden pompano reared in net pens should be 450–490 and 65 g kg^?1.