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 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.     

Effect of dietary vitamin B6 on growth,feed utilization,health and non‐specific immune of juvenile Pacific white shrimp,Litopenaeus vannamei

Six diets were formulated with vitamin B₆ levels (2.6, 32.7, 54.8, 90.7, 119.6 and 247.4 mg kg⁻¹, dry diet) to determine the requirement for juvenile Pacific white shrimp, Litopenaeus vannamei. Triplicate groups of 40 juvenile shrimp (approximately 1.0 g) were provided four times each day to apparent satiation (8 weeks). Weight gain (WG), specific growth rate, feeding efficiency, protein efficiency ratio (PER) and protein productive value of the shrimp were significantly influenced by the vitamin B₆ levels. No significant differences in whole‐body and muscle composition, except for dry matter and protein contents in whole body. Vitamin B₆ concentration in the hepatopancreas significantly increased with the dietary vitamin B₆ level increasing from 2.6 to 32.7 mg kg⁻¹. High‐density lipoprotein cholesterol in the haemolymph improved with the dietary vitamin B₆ levels increasing from 2.6 to 90.7 mg kg⁻¹ diet and no significant differences in low‐density lipoprotein cholesterol, cholesterol, glucose and total protein concentrations. Aspartate aminotransferase, alanine aminotransferase, superoxide dismutase, catalase and lysozyme in the haemolymph were significantly influenced by dietary vitamin B₆ levels. The optimal dietary vitamin B₆ requirements estimated using a two‐slope broken‐line model based on WG and SGR and an exponential model based on the vitamin B₆ concentration in the hepatopancreas were 110.39, 110.08 and 167.5 mg kg⁻¹, respectively.     

Effect of dietary vitamin C on the growth performance,antioxidant ability and innate immunity of juvenile yellow catfish (Pelteobagrus fulvidraco Richardson)

A 12‐week feeding trial was conducted to evaluate the effects of dietary vitamin C on growth performance, antioxidant status and innate immune responses in juvenile yellow catfish, Pelteobagrus fulvidraco. Six isonitrogenous and isolipidic diets (44% crude protein and 7% lipid) were formulated to contain six graded dietary vitamin C (ascorbate‐2‐poly‐ phosphate, ROVIMIX^® STAY‐C^® 35) levels ranging from 1.9 to 316.0 mg kg^?1 diet. The results of present study indicated that fish fed the lowest vitamin C diet had lower weight gain (WG) and specific growth rate (SGR) than those fed the diets supplemented vitamin C. WG and SGR did significantly increase with dietary vitamin C levels increasing from 1.9 to 156.5 mg kg^?1. However, no significant increase was observed with further dietary vitamin C levels increasing from 156.5 to 316 mg kg^?1. Survival, protein efficiency ratio and feed efficiency were not significantly affected by the dietary vitamin C levels. The activities of serum superoxide dismutase, catalase and glutathione peroxidase significantly increased when dietary vitamin C levels increased from 1.9 to 156.5 mg kg^?1, fish fed the lowest vitamin C diet had higher serum malondialdehyde content than those fed the diets supplemented with vitamin C. Fish fed the diet containing 156.5 mg kg^?1 vitamin C had the highest lysozyme, total complement activity, phagocytosis index and respiratory burst of head kidney among all treatments. The challenge test with Aeromonas hydrophila indicated that lower cumulative survival was observed in fish fed the lowest vitamin C diet. Analysis by broken‐line regression of SGR and lysozyme activity indicated that the dietary vitamin C requirement of juvenile yellow catfish was estimated to be 114.5 and 102.5 mg kg^?1 diet, respectively.     

Effects of dietary ethoxyquin on growth,feed utilization and residue in the muscle of juvenile Japanese seabass,Lateolabrax japonicus

Ethoxyquin (EQ) is the most common synthetic antioxidant used for preventing rancidity in fish foodstuffs. However, literature related to the effects of dietary EQ on performance of fish was limited. The present study was conducted to investigate the effects of EQ on performance and EQ residue in muscle of juvenile Japanese seabass Lateolabrax japonicus and to estimate the optimal EQ concentration in the diet. Graded levels [0 (control), 50, 150, 450 and 1350 mg EQ kg^?1 diet] of EQ were added to the basal diet, resulting in five dietary treatments in the experiment. Each diet was fed to triplicate groups of seabass (initial body weight 8.01 ± 0.76 g) for 12 weeks in floating sea cages (1.5 × 1.5 × 2.0 m, 30 fish per cage). Survival ranged from 78.9 to 86.7%, and was irrespective of dietary EQ levels. The specific growth rate (SGR) of fish fed diets supplemented with ≤50 mg kg^?1 EQ had significantly (P < 0.05) higher SGR than fish fed diets supplemented with ≥150 mg kg^?1 EQ, the highest SGR was observed in fish fed diet with 50 mg kg^?1 EQ supplementation. Feed intake (FI) and feed efficiency (FE) were not significantly (P > 0.05) different among dietary treatments. Fish fed diets with 50 and 1350 mg kg^?1 EQ had a significant (P < 0.05) lower body lipid content than fish in the control group. Muscle EQ level significantly increased when dietary EQ increased. Optimal EQ concentration estimated by polynomial regression based on maximum growth of juvenile Japanese seabass was 13.78 mg kg^?1 diet.     

Effects of various dietary levels of copper hydroxychloride on growth performance and tissue response in Pacific white shrimp Litopenaeus vannamei fed practical diets

Two trials were conducted to evaluate the performance of Pacific white shrimp Litopenaeus vannamei offered diets containing various copper (Cu) levels from Cu hydroxychloride (Cu₂(OH)₃Cl) containing 58.81% copper in the clear water recirculating system. In both trials, the basal diet (360 g kg^?1 protein, 80 g kg^?1 lipid) containing approximately 10 mg Cu kg^?1 was primarily comprised of fishmeal, soybean meal, corn protein concentrate and whole wheat. In trial 1, test diets were produced supplementing the basal diet with 5, 10, 20, 40 and 60 mg Cu kg^?1 from Cu hydroxychloride. Four replicate groups of 15 shrimp per tank (initial weight 0.28 g) were offered diets in slight excess over 8 weeks. In trial 2, the basal diet was supplemented with 30, 90, 150, 210 and 270 mg Cu kg^?1 from Cu hydroxychloride. Seven replicate groups of 15 shrimp per tank (initial weight 0.22 g) were offered feed in slight excess over 7 weeks. At the end of the two growth trials, no significant differences were observed in final biomass, final mean weight, percentage weight gain, feed conversion ratio (FCR) and survival. In trial 1, the Cu concentrations of the carapace, hepatopancreas and whole shrimp linearly increased with increasing dietary Cu supplements. In trial 2, polynomial regression of Cu concentrations of the carapace, hepatopancreas and whole shrimp against analysed dietary Cu content indicated that a plateau was reached at 215 mg analysed Cu kg^?1. Results of this study indicate that there was no negative effect of high levels of Cu supplement with regard to growth and survival. Tissue levels generally increased up to around 200 mg Cu kg^?1 diet and then decreased, possibly indicating a shift in physiology.     

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.     

Dietary choline requirement in slight methionine‐deficient diet for juvenile gibel carp (Carassius auratus gibelio)

A 10‐week feeding trial was conducted in a flow‐through system to determine dietary choline requirement for juvenile gibel carp (Carassius auratus gibelio) (5.5 ± 0.1 g). Purified basal diet was formulated using vitamin‐free casein as protein source. Choline chloride was supplemented to the basal diet to formulate seven diets containing 76.1, 163, 356, 969, 1457, 2024 and 4400 mg kg^?1 choline. Dietary methionine was 0.58%, less than the requirement (0.69%). The results indicated that specific growth rate (SGR) was higher in the fish fed 2024 mg kg^?1 diet than the control group. Feeding rate and feed efficiency were not significantly affected. Protein productive value increased as dietary choline increased from 76.1 to 2024 mg kg^?1 diet and was lower in the fish fed the diet containing 4400 mg choline kg^?1 diet. Serum high‐density lipoprotein cholesterol (HDL‐C) and total cholesterol significantly increased with increasing dietary choline up to 1457 mg kg^?1, and no differences were found with further increase. Fish carcass fat contents decreased significantly with increased dietary choline. Hepatic lipid contents increased with dietary choline up to 1457 mg kg^?1 and then decreased. Quadric regression of SGR and plasma HDL‐C indicted dietary choline requirement was 2500 and 2667 mg kg^?1 diet, respectively.     

Growth,digestive and absorptive abilities and antioxidative capacity in the hepatopancreas and intestine of young grass carp (Ctenopharyngodon idellus Val.) fed graded levels of dietary manganese

To study the effects of manganese on growth performance, digestive and absorptive abilities, as well as the antioxidative capacity in the hepatopancreas and intestine, young grass carp (Ctenopharyngodon idellus Val.) (264 ± 1 g) were fed diets containing graded levels of manganese at 3.65 (control), 8.62, 13.48, 18.24, 22.97 and 27.86 mg kg^?1 diet for 8 weeks. Per cent weight gain (PWG) and feed intake were the poorest in fish fed the basal diet (P < 0.05). The activities of trypsin, lipase and alkaline phosphatase in the intestine were significantly enhanced with dietary manganese level at 13.48 mg kg^?1 diet (P < 0.05). Additionally, in the hepatopancreas and intestine, the protein carbonyl and malondialdehyde contents were the lowest in fish fed the diet with dietary manganese level at 13.48 mg kg^?1 diet (P < 0.05), while the anti‐hydroxyl radical capacities, manganese superoxide dismutase (MnSOD), glutathione peroxidase and glutathione‐S‐transferase activities were significantly enhanced with dietary manganese level at 13.48 mg kg^?1 diet (P < 0.05). Moreover, the catalase activity and glutathione content in the intestine were the highest in fish fed the diet with dietary manganese level at 18.24 mg kg^?1 diet (P < 0.05). These results indicated that optimum dietary manganese promoted growth, enhanced the digestive and absorptive abilities, and improved the antioxidative capacity in young grass carp. Based on the quadratic regression analysis for PWG and intestinal MnSOD activity, the manganese requirements for young grass carp with the initial body weight of 264 g were 16.91 and 18.21 mg kg^?1 diet respectively.     

Effects of dietary L‐carnitine level on growth performance,body composition and antioxidant status in beluga (Huso huso L. 1758)

A 17‐week feeding trial was carried out to evaluate the effects of dietary L‐carnitine level in beluga, Huso huso. A total of fish averaging 1247 ± 15.6 g (mean ± SD) were randomly distributed into 18 fibreglass tanks, and each tank holding 10 fish was then randomly assigned to one of three replicates of six diets with 50, 150, 350, 650, 950 and 1250 mg L‐carnitine kg^?1 diet. At the end of 17 weeks of feeding trial, average weight gain (WG), feed efficiency (FE), protein efficiency ratio (PER) and condition factor (CF) of fish fed 350 mg kg^?1 diet were significantly (P < 0.05) higher than those of fish fed 50, 150, 950 and 1250 mg kg^?1 diets. WG, FE, PER and CF of beluga fed 650 mg kg^?1 diet were also significantly higher than those of fish fed 50, 950 and 1250 mg kg^?1 diets. Whole body and muscle protein were significantly improved by the elevation of dietary L‐carnitine level up to 350 mg kg^?1. Liver superoxide dismutase and glutathione peroxidase activities of fish fed 350 and 650 mg kg^?1 diets were significantly higher than those of fish fed 50, 950 and 1250 mg kg^?1 diets. The dietary L‐carnitine level of 350–650 mg kg^?1 diet could improve growth performance, feed utilization, protein‐sparing effects of lipid, antioxidant defence system and reproductive success. Polynomial regression of WG suggested that the optimum dietary L‐carnitine level was 480 mg kg^?1 diet. Therefore, these results may indicate that the optimum dietary L‐carnitine could be higher than 350 but <650 mg kg^?1 diet in beluga reared in intensive culture conditions.     

Dose‐dependent protective effects of dietary selenium on abalone Haliotis discus hannai Ino against the toxicity of waterborne copper

This study was designed to assess the protective effects of dietary selenium (Se) on abalone Haliotis discus hannai Ino against the toxicity of waterborne copper (Cu). A 60‐day feeding trial was conducted in a static water system for abalone (initial weight: 3.17 ± 0.01 g) exposed to 0.02 mg L^?1 of waterborne Cu. The animals were fed one of the three experimental diets with 0.10, 1.31 and 4.20 mg kg^?1 of Se from Na₂SeO₃·5H₂O respectively. Results showed that the abalone fed 1.31 mg kg^?1 of dietary Se had the lowest Cu concentration in shell, muscle, mantle, gill, hepatopancreas and serum. Meanwhile, the significant lowest contents of malondiadehyde and protein carbonyl in hepatopancreas were also found in the treatment with 1.31 mg kg^?1 of dietary Se (P < 0.05). In addition, this treatment had significant higher glutathione content and thioredoxin reductase activity in hepatopancreas (P < 0.05). However, the activity of Se‐dependent glutathione peroxidase (Se‐GPx) was significantly decreased in the treatment with 4.20 mg kg^?1 of dietary Se (P < 0.05). In this treatment, the protein carbonyl content in hepatopancreas was significantly higher than that in the group with 1.31 mg kg^?1 of dietary Se (P < 0.05). In conclusion, in terms of anti‐oxidation and Cu accumulation, the protective effects of dietary Se on abalone against waterborne Cu were dose‐dependent. The 1.31 mg kg^?1 of dietary Se had this effect, but not 4.20 mg kg^?1 of dietary Se. Moreover, the latter increased the oxidative stress in abalone exposed to the waterborne Cu.     

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.     

Effects of dietary manganese source and supplemental levels on growth performance,antioxidant enzymes activities,tissue Mn concentrations and cytosolic manganese superoxide dismutase (cMnSOD) mRNA expression level of juvenile Litopenaeus vannamei

This experiment was conducted to study the effects of different forms and levels of manganese (Mn) on the growth performance, antioxidant activities, tissue Mn content and cytosolic manganese superoxide dismutase (cMnSOD) gene expression of Litopenaeus vannamei. Treatments consisted of 0, 10, 20, 30, 40 and 60 mg Mn kg^?1 from manganese sulphate (Mn‐S) and manganese methionine (Mn‐Met), providing the actual dietary value of 5.17, 15.62, 25.55, 34.22, 44.48 and 67.90 mg Mn kg^?1 Mn‐S, and 5.17, 15.71, 25.36, 35.86, 45.16 and 65.06 mg Mn kg^?1 Mn‐Met, respectively. Each diet was fed to triplicate groups of L. vannamei (initial body weight: 1.925 ± 0.002 g) in a recirculated fresh water rearing system for 8 weeks. Weight gain rate (WGR) increased in prawns provided with from 25.55 to 44.48 mg Mn kg^?1 Mn‐S and 15.71 to 45.16 mg Mn kg^?1 Mn‐Met and then declined above these levels. The lowest protein efficiency ratio (PER) and the highest feed conversion rate (FCR) were observed in prawns fed the control diet (P < 0.05) and showed no significant differences among other treatments (P > 0.05). Survival rate (SR) was not affected by the dietary treatments (P > 0.05). Total SOD and Mn‐SOD activities were higher in the hepatopancreas of prawns fed with Mn‐supplemented diets from 15.71 to 44.48 mg Mn kg^?1 (P < 0.05). On the contrary, malondialdehyde (MDA) content was lower in the hepatopancreas of prawns fed the basal diet (P < 0.05). Mn concentrations in the hepatopancreas and muscles increased with increasing levels of dietary Mn supplementation. Moreover, Mn accumulation was lower in the muscle than in the hepatopancreas of the prawns. The mRNA expression of cMnSOD gene in the hepatopancreas of prawns was upregulated with increasing dietary Mn levels of Mn‐S from 25.55 to 44.48 mg Mn kg^?1, Mn‐Met from 15.71 to 45.16 mg Mn kg^?1 and then plateaued above these levels. Broken‐line regression analysis of WGR indicated that the optimal dietary Mn requirements for juvenile L. vannamei were 32.26 mg Mn kg^?1 Mn‐S and 23.90 mg Mn kg^?1 Mn‐Met, respectively.     

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.     

The effects of dietary vitamin C on growth performance,serum enzymes activities and resistance to Vibrio alginolyticus challenge of yellow drum Nibea albiflora

A 9‐week feeding trial was conducted to determine the optimal dietary vitamin C requirement and its effects on serum enzymes activities and bacterial resistance in the juvenile yellow drum Nibea albiflora (initial weight 33.2 ± 0.10 g). Six practical diets were formulated containing vitamin C 2.1, 45.3, 89.6, 132.4, 178.6 and 547.1 mg kg^?1 diet supplied as l ‐ascorbyl‐2‐monophosphate. The fish fed 547.1 mg kg^?1 diet showed a significantly higher survival than that fed 2.1 mg kg^?1 diet. The weight gains and specific growth rate of the fish fed 2.1 mg kg^?1 diet were significantly lower than those of the fish fed 89.6–547.1 mg kg^?1 diets. The liver vitamin C concentration firstly increased with increasing dietary vitamin C supply from 2.1 to 178.6 mg kg^?1 diet and then stabilized. The serum superoxide dismutase activities of the fish fed 547.1 mg kg^?1 diet were significantly lower than those of the fish fed 2.1–89.6 mg kg^?1 diet. The fish fed 2.1 mg kg^?1 diet had a significantly higher alkaline phosphatase activity than those in the other groups except the 45.3 mg kg^?1 group. Fish that received diets containing vitamin C at 547.1 mg kg^?1 had significantly higher nitro blue tetrazolium and lysozyme activity, and fish that received diets containing vitamin C at 45.3–547.1 mg kg^?1 exhibited resistance against Vibrio alginolyticus infection. The dietary vitamin C requirement of the juvenile yellow drum was established based on broken‐line model of weight gain to be 142.2 mg l ‐ascorbyl‐2‐monophosphate kg^?1 diet.     

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 graded levels of dietary thiamine on the growth performance,body composition and haemato‐biochemical parameters of juvenile Sclizothorax prenanti

This study was conducted to determine dietary thiamine requirement of juvenile Sclizothorax prenanti and evaluate the effect of dietary thiamine levels on growth performance, body composition and haemato‐biochemical parameters for this fish species. The seven experimental diets were formulated to contain the graded levels of thiamine (0, 10, 20, 30, 40, 60 and 100 mg kg^?1 diet, respectively), providing the actual dietary thiamine values of 0.31 (control), 9.82, 21.49, 29.83, 41.66, 62.24 and 114.58 mg kg^?1 diet, respectively. Each diet was assigned to three replicate groups of S. prenanti (initial body weight: 13.46 ± 0.28 g, means ± SD) for 60 days. Increasing dietary thiamine level up to 21.49 mg kg^?1 diet increased weight gain rate (WGR), specific growth rate (SGR), feed efficiency (FE) and protein efficiency ratio (PER) (P < 0.05), beyond which they remained nearly unchanged. Similarly, hepatic thiamine concentration and several serum biochemical parameters (transketolase activity, triglyceride and total cholesterol contents) increased with increasing levels of thiamine up to 21.49 mg kg^?1 diet (P < 0.05) and, thereafter, remained almost constant. However, no significant differences in body composition (moisture, protein, lipid and ash contents) were found among dietary thiamine treatments (P > 0.05). Analysis by the broken‐line regression of WGR, SGR, FE, PER, hepatic thiamine concentration and serum transketolase activity indicated that dietary thiamine requirements in juvenile S. prenanti were 18.45–25.91 mg kg^?1 diet.     

Dietary manganese requirement for juvenile cobia,Rachycentron canadum L

A 10‐week feeding trial was conducted to estimate the optimum dietary manganese requirement for juvenile cobia, Rachycentron canadum L. The basal diet was formulated to contain 501 g kg^?1 crude protein from vitamin‐free casein, gelatin and fish protein concentrate. Manganese sulphate was added to the basal diet at 0 (control group), 6, 12, 18, 24 and 36 mg Mn kg^?1 diet providing 5.98, 7.23, 16.05, 23.87, 28.87 and 41.29 mg Mn kg^?1 diet, respectively. Each diet was randomly fed to three replicate groups of cobia for 10 weeks, and each tank was stocked with 30 fish (initial weight, 6.27 ± 0.03 g). The manganese concentration in rearing water was monitored during the feeding period and was < 0.01 mg L^?1. Dietary manganese level significantly influenced survival ratio (SR), specific growth ratio (SGR), feed efficiency ratio (FER) and the manganese concentrations in the whole body, vertebra and liver of cobia. When the dietary manganese level rose from 5.98 mg kg^?1 to 23.87 mg kg^?1, the superoxide dismutase (SOD; EC 1.15.1.1) activities in liver also increased (P < 0.05). But there was no significant change in SOD activities for the groups fed with diets containing manganese level higher than 23.87 mg kg^?1. On the basis of broken‐line regression of SGR, manganese concentration in whole body and vertebra the manganese requirements of juvenile cobia were 21.72 mg kg^?1, 22.38 mg kg^?1 and 24.93 mg kg^?1 diet in the form of manganese sulphate, respectively.     

Effects of dietary magnesium on the growth,carapace strength and tissue magnesium concentrations of soft‐shelled turtle,Pelodiscus sinensis (Wiegmann)

A feeding trial was conducted to evaluate the effects of dietary magnesium on the growth, carapace strength, tissue and serum Mg concentration of soft‐shelled turtles, Pelodiscus sinensis (Wiegmann). Juvenile soft‐shelled turtles of approximate 5.4 g body weight were fed diets with seven levels of Mg (48, 206, 369, 670, 955, 1195 and 1500 mg Mg kg^?1) for eight weeks. No significant difference (P ≥ 0.05) was found in weight gain (WG), feed conversion ratio or protein efficiency ratio among treatments. However, the WG of turtles continued to increase with increasing dietary Mg levels up to 670 mg kg^?1, beyond which the WG levelled off. The plasma alkaline phosphatase activity and the muscle, bone Mg concentrations of the turtles increased with the increasing dietary Mg levels between 48 and 955 mg kg^?1, beyond which the tissue Mg concentrations remained relatively constant. Furthermore, the carapace strengths of turtles fed with the control diet of 48 mg Mg kg^?1 were significantly weaker (P < 0.05) than that of turtles fed with diets containing higher Mg levels. Based on a broken‐line modelling analysis, the required dietary Mg level for the optimal WG of juvenile soft‐shelled turtles was estimated to be approximately 650 mg kg^?1. By contrast, the required dietary Mg levels for turtles to reach the optimal muscle and bone Mg concentrations were 1050 and 1000 mg kg^?1 respectively. The required dietary Mg level for maximal alkaline phosphatase activity was approximately 980 mg kg^?1.     

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.