Protective effects of dietary selenium on abalone Haliotis discus hannai against the toxicity of waterborne cadmium

This study was conducted to investigate protective effects of dietary selenium (Se) on abalone Haliotis discus hannai Ino against the toxicity of cadmium (Cd). A 60‐day feeding trial was conducted with abalone (initial weight: 3.17 ± 0.01 g), which were exposed to 0.34 mg/L of waterborne Cd. During a feeding trial, abalone were fed graded levels of Se at 0.10 (controls), 1.31, and 4.20 mg/kg diet respectively. Results showed that there was no significant difference in specific growth rate and survival rate of abalone among the three treatments. Compared with the controls, dietary Se significantly decreased Cd concentrations in serum, muscle, mantle, gill, mantle, and hepatopancreas of abalone. Besides, compared with the controls, dietary Se significantly increased metallothionein concentration in the hepatopancreas of abalone. Additionally, compared with the controls, dietary Se significantly decreased concentrations of malondiadehyde and protein carbonyl in hepatopancreas of abalone. Meanwhile, compared with the controls, dietary Se significantly increased activities of glutathione peroxidase, thioredoxin reductase, and thioredoxin peroxidase, and concentration of glutathione in the hepatopancreas of abalone. Based on the data above, in abalone, dietary Se showed protective effects against waterborne Cd.     

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.     

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.     

Dietary selenium requirement for on‐growing gibel carp (Carassius auratus gibelio var. CAS III)

A 12‐week growth trial was conducted in a flow‐through system to determine dietary selenium (Se) requirement for on‐growing gibel carp (initial body weight: 76.2 ± 0.05 g, mean ± SEM). Selenomethionine was supplemented to the basal diet to formulate seven semi‐purified diets containing 0.26, 0.58, 0.72, 1.14, 1.34, 1.73 and 2.09 mg Se kg^?1 diet. The results showed that plasma superoxide dismutase (SOD) activity significantly increased when fish were fed with 0.58 mg Se kg^?1 diet (P < 0.05) and then decreased at 2.09 mg Se kg^?1 diet (P < 0.05). Plasma T‐AOC activity was higher in fish fed with 0.72 mg Se kg^?1 diet (P < 0.05) and plasma malondialdehyde (MDA) was higher in fish fed with 0.26 mg Se kg^?1 diet (P < 0.05). When fish were fed 1.14 mg Se kg^?1 diet, hepatic GSH‐Px, T‐AOC, GSH and CAT activities were significantly higher than those fed with 0.26 mg Se kg^?1 diet (P < 0.05). Hepatic superoxide dismutase (SOD) activity was higher at 1.34 mg Se kg^?1 diet (P < 0.05). Fish liver Se concentrations were significantly higher when fed with 0.72 mg Se kg^?1 diet (P < 0.05) and then kept constant when Se ≥ 0.72 mg kg^?1 (P > 0.05). Whole‐body and muscle Se concentrations were higher when fed with 1.34 mg Se kg^?1 diet (P < 0.05) and kept a plateau when Se ≥ 1.34 mg kg^?1 (P > 0.05). In conclusion, based on broken‐line regression of hepatic Se concentrations, hepatic SOD activity and hepatic T‐AOC activity, dietary Se requirements for on‐growing gibel carp was 0.73 mg kg^?1, 1.12 mg kg^?1 and 1.19 mg kg^?1 diet respectively.     

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.     

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.     

Effects of dietary inorganic copper on growth performance and immune responses of juvenile beluga,Huso huso

A 12‐week feeding trial was conducted to evaluate the optimum dietary inorganic copper (copper sulphate) in juvenile beluga, Huso huso. Eight semi‐purified diets containing 1.1 (Cu_1.0), 3.5 (Cu_4.0), 7.1 (Cu_7.0), 9.7 (Cu₁₀), 13.1 (Cu₁₃), 25.1 (Cu₂₅), 49.9 (Cu₅₀) and 195 (Cu₁₉₅) mg Cu kg^?1 diet in the form of CuSO₄.5H₂O were fed to fish of initial body weight 8.49 ± 0.32 g and length 11.85 ± 0.66 cm (mean ± SD) in triplicate groups in a flow‐through system. Weight gain (WG) of fish fed Cu₁₀ and Cu₁₃ diets was significantly higher than that of fish fed Cu_1.0, Cu_4.0, Cu₂₅, Cu₅₀ and Cu₁₉₅ diets (P < 0.05). Whole‐body and muscle crude protein increased with dietary Cu up to the supplementation level of 13.1 mg kg^?1 diet and then decreased. Whole‐body lipid content was negatively correlated, while whole‐body ash was positively correlated with dietary copper concentration. Hepatic copper–zinc superoxide dismutase activity of fish fed Cu₁₀ and Cu₁₃ diets was significantly higher than that of fish fed Cu_1.0, Cu_4.0 and Cu₁₉₅ diets. Hepatic thiobarbituric acid‐reactive substances of fish fed Cu₁₃ diet was significantly lower than those of fish fed the other diets except for that of fish fed Cu₁₀ diet. Aspartate aminotransferase, alanine aminotransferase and copper accumulation in tissues increased with dietary copper. Broken‐line analysis of WG suggested that the optimum dietary Cu level was 10.3 mg Cu kg^?1 diet. Therefore, these results may indicate that the optimum dietary Cu levels could be greater than 10.3 mg Cu kg^?1 diet but less than 13.1 mg Cu kg^?1 diet in juvenile beluga, when copper sulphate is used as the dietary source of inorganic copper.     

Effect of dietary chitosan on growth performance,haematology, immune response,intestine morphology,intestine microbiota and disease resistance in gibel carp (Carassius auratus gibelio)

A 75‐day experiment was conducted with juvenile gibel carp (Carassius auratus gibelio) (4.80 ± 0.01 g) to evaluate effects of dietary chitosan on fish growth performance, haematology, intestine morphology and immune response. Six isonitrogenous (crude protein: 383 g kg^?1), isolipid (97.5 g kg^?1) and isocaloric (gross energy: 16.7 kJ g^?1) diets were formulated to contain 0, 1800, 4000, 7500, 10 000, 20 000 mg kg^?1 chitosan, respectively. The results showed that the growth was depressed when the fish fed with 10 000 mg kg^?1 chitosan. Serum cholesterol, triglyceride and low‐density lipoprotein decreased in 10 000 and 20 000 mg kg^?1 chitosan. On day 75, blood leucocyte phagocytic activity respiratory burst and alternative pathway of complement haemolytic activity were enhanced in 4000 mg kg^?1 chitosan. The number of goblet cell, intraepithelial lymphocyte of mid‐intestine and microvilli height of distal intestine increased at 4000 mg kg^?1 dietary chitosan. Dietary chitosan modulated intestine microbiota, depressed pathogen bacteria Aeromonas veronii‐like and improved Cellulomonas hominis‐like, Bacillus oceanisediminis‐like and two uncultured bacterium‐like species on day 75. Dietary 7500 and 10 000 mg kg^?1 chitosan enhanced the protection against Aeromonas hydrophila infection. In conclusion, oral administration of dietary 7500 mg kg^?1 chitosan for 75 days is recommended for the survival of gibel carp.     

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.     

Effects of the dietary protein to energy ratio on growth,feed utilization and body composition in Macrobrachium nipponense

Oriental river prawn (Macrobrachium nipponense) has been widely cultured in Asian countries. However, its nutritional studies are very limited. In the present 8‐week study, we investigated the effects of dietary protein to energy ratio (P/E ratio) on the growth, feed utilization and body composition in juvenile M. nipponense (initial weight 0.302 ±0.03 g). Two‐factor experiment was designed and nine semi‐purified diets were formulated to contain three lipid levels (20, 80 and 140 g kg^?1) and three protein levels (330, 380 and 430 g kg^?1), producing P/E ratios from 16.5 to 23.4 mg KJ^?1 protein. The results indicated that the growth, survival rate and protein efficiency were dose dependently improved by the increased dietary lipid, but not dietary protein content. Increased dietary lipid content and/or protein content increased lipid accumulation in whole body, hepatopancreas and muscle, but did not change the feed intake and hepatopancreas weight. In conclusion, our present study indicated that M. nipponense is a species with relatively high‐energy requirement. It could utilize dietary lipid content up to 140 g kg^?1, while the dietary protein with more than 330 g kg^?1 would not promote growth and protein efficiency. Taken together, 330 g kg^?1 dietary protein and 140 g kg^?1 dietary lipid level with P/E ratio 16.49 could be optimum for M. nipponense.     

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.     

Effect of dietary selenium level on growth performance,body composition and hepatic glutathione peroxidase activities of largemouth bass Micropterus salmoide

An 8‐week growth trial was conducted to determine the effect of dietary selenium (Se) level on growth performance, body composition and hepatic glutathione peroxidase (GPx) activities of largemouth bass. Sodium selenite was added to the fish meal basal diet at 0, 0.2, 0.4, 0.6, 0.8 and 1.0 mg kg^?1 Se providing 0.97, 1.17, 1.42, 1.60, 1.85 and 2.06 mg Se kg^?1 diet respectively. Each diet was fed to triplicate groups of fish (initial mean body weight: 4.95 ± 0.03 g) in a closed indoor recirculating system. The Se concentration in the rearing water was not detectable during the whole experimental period. The highest weight gain was obtained in fish fed diets with 1.60 mg Se kg^?1, which was significant higher (P < 0.05) than the basal diet with 0.97 mg Se kg^?1 and did not differ significantly (P > 0.05) with the other treatments. Feed conversion ratio, protein efficiency ratio, protein productive value, apparent digestibility coefficients of dry matter and muscle composition were not significantly impacted (P > 0.05) by dietary treatments. Fish fed diets with ≥1.42 mg Se kg^?1 obtained higher liver lipid contents than treatments with lower dietary Se levels. Hepatic malondialdehyde (MDA) was unchanged (P > 0.05) in relation to dietary Se concentration. Hepatic GPx and glutathione reductase (GR) activities markedly increased and decreased (P < 0.05) with increasing dietary Se concentration, respectively, and both reached a plateau with ≥1.85 mg Se kg^?1. Based on growth performance, hepatic MDA and enzymatic responses of GPx and GR, the highest Se concentration (2.06 mg kg^?1) employed in our study was not harmful for largemouth bass, and the optimal dietary level should be 1.60–1.85 mg Se kg^?1 from sodium selenite, at a dietary vitamin E level of 400 IU kg^?1.     

Effect of γ‐aminobutyric acid supplementation on growth performance,endocrine hormone and stress tolerance of juvenile Pacific white shrimp,Litopenaeus vannamei,fed low fishmeal diet

An 8‐week feeding trial was conducted to evaluate the optimum dietary γ‐aminobutyric acid (GABA) level in low fishmeal diet for juvenile Pacific white shrimp, Litopenaeus vannamei. Six practical diets (449 g kg^?1 protein, 87 g kg^?1 lipid) supplemented with graded levels of GABA (0, 50, 100, 150, 200, 250 mg kg^?1) were formulated. Each diet was randomly assigned to triplicate groups of 30 shrimps (approximately 0.44 g), and the shrimps were fed four times a day to apparent satiation. Weight gain and gain rate were significantly increased with the supplementation of GABA (P < 0.05). Hepatosomatic index and survival were also significantly influenced by the dietary GABA levels (P < 0.05) and show a similar trend to those of growth performance. Insulin and neuropeptide Y concentrations in blood were increased with the supplementation of GABA. In total, 150 mg GABA kg^?1‐supplemented diets significantly increased the survival after 12, 24 and 36 h of NH₃ stress, also increased the total antioxidant capacity, total superoxide dismutase, catalase, antihydroxyl radical and phenoloxidase activities before and after the 36 h NH₃ stress compared to basic group. These results clearly indicated that GABA could improve growth performance, antioxidative capacity and resistance against NH₃ stress in L. vannamei, and 150 mg kg^?1 GABA supplementation was suitable for L. vannamei fed with low fishmeal diet.     

Effects of dietary folic acid on growth,antioxidant capacity,non‐specific immune response and disease resistance of juvenile Chinese mitten crab Eriocheir sinensis (Milne‐Edwards, 1853)

An 8‐week study was conducted to determine folic acid requirement and its effect on antioxidant capacity and immunity in juvenile Chinese mitten crab Eriocheir sinensis (Milne‐Edwards, 1853), followed by a challenge assay with the pathogen Aeromonas hydrophila for 2 weeks. Folic acid was added to a basal diet at seven levels (0, 0.5, 1.0, 2.0, 4.0, 8.0, 16.0 mg folic acid kg^?1 diet), and a diet free of folic acid and vitamin B₁₂ was also included as a control. Crabs were fed twice daily in 32 tanks with 7.76–8.17 mg oxygen L^?1, 25.0–31.0 °C and 7.5–8.3 pH. Growth and feed efficiency were significantly greater in crabs fed ≥2.0 mg folic acid kg^?1, but not significantly different between crabs fed diets >2.0 mg folic acid. The superoxide dismutase activity and glutathione S‐transferase activity were highest in crabs fed ≥2.0 mg folic acid kg^?1, followed by those fed 0.5 and 1.0 mg folic acid kg^?1, and the control diet. The malondialdehyde content was highest in crabs fed the control diet, followed by those fed 0 mg folic acid kg^?1, and the lowest value occurred in those fed ≥0.5 mg folic acid kg^?1. Phenoloxidase activity and total haemocytes were significantly higher in crabs fed ≥2.0 mg folic acid kg^?1 than other diets. Crabs fed 2.0 mg folic acid kg^?1 had the highest lysozyme, acid phosphatase and alkaline phosphatase activities but the lowest cumulative mortality. The optimum dietary folic acid requirement by E. sinensis was estimated at 2.29–2.90 mg kg^?1 diet.     

A tolerance and safety assessment of daidzein in a female fish (Carassius auratus gibelio)

Daidzein is widely used in farmed animals as a dietary additive. However, limited information is available about its use in aquaculture. The effects of daidzein inclusion in the diet of gibel carp was assessed in terms of growth performance, immune response, disease resistance, antioxidant activity, hormone levels, daidzein tissue residues, as well as intestinal and liver morphology. The dietary daidzein inclusion levels were 0, 40, 200 and 400 mg kg^?1 and six replicates of 30 fish were used for each group. No mortality was observed during the 80‐day feeding trial. The growth performance of experimental fish was not significantly affected by dietary daidzein supplementation. However, the non‐specific immune responses, resistance to Aeromonas hydrophila, antioxidant activities, 17β‐oestradiol level, vitellogenin concentration, gonadosomatic index (GSI) and intestinal morphology were significantly affected by dietary daidzein. A dietary dose of 400 mg kg^?1 daidzein significantly decreased the GSI, increased 17β‐oestradiol and vitellogenin concentrations, and impaired the intestinal structure. The daidzein residue in muscle of gibel carp was increased by the high level (400 mg kg^?1) of dietary daidzein. Equol was not detected in fish muscle among all treatments. The present study proved that 40 mg kg^?1 daidzein was safe to be included in diets of gibel carp, and a safety margin of 5 folds of the use‐level (40 mg kg^?1) was determined.     

Dietary vitamin C requirement of genetically improved farmed Tilapia,Oreochromis Niloticus

A 12‐week growth experiment was conducted to quantify the appropriate dietary vitamin C requirement for GIFT tilapia Oreochromis niloticus. Triplicate groups of 25 experimental tilapia [initial body weight: (70.0 ± 1.6) g] were cultured in 5.6‐m³ aquaria (r = 1.5 m,h = 0.8 m) and fed with semi‐purified diets containing six levels [6.1 (un‐supplemented diet], 23.8, 41.9, 85.1, 167.4 and 339.0 mg kg^?1 diet respectively) of vitamin C (supplied as L‐ascorbyl‐2‐polyphosphate). The results showed that, increasing dietary vitamin C level up to 41.9 mg kg^?1 diet increased weight gain rate of tilapia, beyond which it remained nearly unchanged. Vitamin C contents in liver and muscle presented first increased linearly then tended to reach saturation at high vitamin C (167.4 and 339.0 mg kg^?1) treatments. Muscle collagen content significantly increased with increasing dietary vitamin C levels. Whole‐body lipid content significantly increased, whereas ash content significantly declined, but moisture and crude protein content showed no significant difference with the increasing of dietary vitamin C. The blood chemistry analysis showed that dietary vitamin C had significant effects on enzyme activities of serum alkaline phosphatase, aspartate aminotransferase and alanine aminotransferase. Significant effects were also observed on albumin and total protein content of serum, but haemoglobin content showed no significant differences among all the treatments. The vitamin C requirement for GIFT tilapia was estimated to be 45.0 mg kg^?1 diet based on maximum growth, 114.9 and 118.6 mg kg^?1 diet based on maximum liver and muscle vitamin C concentration respectively.     

Estimation of dietary vitamin A requirement of juvenile soft‐shelled turtle,Pelodiscus sinensis

A feeding trial was conducted to evaluate the dietary vitamin A requirement of the soft‐shelled turtle Pelodiscus sinensis. Turtles with an approximate body weight of 6.8 g were fed diets containing 0–4.58 mg kg^?1 (15 251 IU) vitamin A (retinyl acetate) for 8 weeks. Turtles fed diets without vitamin A showed the lowest growth performance. The animals gradually gained weight when dietary vitamin A increased from 0 to 3.6 mg kg^?1. Liver vitamin A gradually increased with supplementation of dietary vitamin A of up to 2.7 mg kg^?1. Beyond this concentration, the vitamin A in the liver significantly increased. Data analysis using a polynomial regression or exponential model showed that the estimated dietary vitamin A requirement for juvenile soft‐shelled turtles based on weight gain, red blood cell count and liver vitamin A measurements was 3.48, 2.84 and 2.58 mg kg^?1, respectively.     

Effects of dietary selenium on the growth,selenium status,antioxidant activities,muscle composition and meat quality of blunt snout bream,Megalobrama amblycephala

An 8‐week feeding trial was performed to investigate effects of dietary selenium (sodium selenite, Na₂SeO₃; selenium nanoparticle, Nano‐Se; selenium yeast, Se‐yeast) on the growth, selenium status, antioxidant activities, muscle composition and meat quality of blunt snout bream. Na₂SeO₃ and Nano‐Se were supplemented at 0.2 mg Se kg^?1, and Se‐yeast was supplemented at 0.1, 0.2, 0.4 and 0.8 mg Se kg^?1 in basal diet; no Se was added as a control. The results indicated that groups of 0.2 and 0.4 mg kg^?1 Se‐yeast had significantly higher weight gain and Nano‐Se, 0.2, 0.4 mg kg^?1 Se‐yeast had significantly lower feed conversation ratio compared with the control group. The Se concentrations of whole body, muscle and liver linearly increased with increasing dietary Se‐yeast levels. Group of 0.4 mg kg^?1 Se‐yeast significantly increased activities of catalase and glutathione peroxidase. Muscle colour of Nano‐Se, 0.2, 0.4 mg kg^?1 Se‐yeast groups, the water‐holding capacity of 0.4, 0.8 mg kg^?1 Se‐yeast groups showed significant differences compared with the control group. The results suggest that Se‐yeast and Nano‐Se had a better growth performance than Na₂SeO₃ at 0.2 mg Se kg^?1, and supplementing appropriate Se‐yeast in diet can increase antioxidant activities and enhance meat quality of blunt snout bream.     

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.     

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.