Dietary manganese requirement of juvenile grass carp (Ctenopharyngodon idella Val.) based on growth and tissue manganese concentration

A growth trial was conducted to estimate the optimum concentration of dietary Manganese (Mn) for grass carp (Ctenopharyngodon idella). Triplicate groups of grass carp (3.97 ± 0.05 g) were fed diets containing graded levels (4.0, 8.9, 13.8, 18.7, 23.6 and 33.3 mg kg^?1) of Mn for 8 weeks. Weight gain, specific growth rate and feed efficiency were linearly increased up to the 18.7 mg kg^?1 dietary Mn and then levelled off beyond this level. For body composition, lipid contents in whole body, muscle and liver decreased significantly with increasing dietary Mn level. Grass carp fed with dietary Mn levels higher than 19.7 mg kg^?1 significantly decreased condition factor. Whole body, vertebrae and scales mineralization were all affected significantly by dietary Mn levels. Mn contents in whole body, vertebrae and scales were linearly increased up to the 18.7 mg kg^?1 dietary Mn and then levelled off beyond this level. Contrarily, Ca and P contents seem to be inversely related to dietary Mn. However, dietary Mn levels had no significant effect on body Fe contents. Broken‐line analysis indicated that 20.6 mg kg^?1 dietary Mn was required for maximal tissue Mn storage, as well as satisfied for the optimal growth of juvenile grass carp.     

Increased dietary phosphorous prevents vertebral deformities in triploid Atlantic salmon (Salmo salar L.)

Triplicate groups of triploid and diploid Atlantic salmon were fed diets with a low (LP, total P: 7.1 g kg^?1), medium (MP, total P: 9.4 g kg^?1) or high (HP, total P: 16.3 g kg^?1) phosphorous (P) level from first feeding (0.18 g) to transfer to sea water (~50 g, duration: 203 days) and subsequently fed a commercial diet in sea water for 426 days (~3 kg). This study examined the short‐ and long‐term effects of dietary P on freshwater performance (mortality, growth), vertebral deformities (radiology), bone cell activity (ALP and TRACP enzyme activity in vertebrae and scales, and fgf23, bgp and igf‐I relative gene expression in vertebrae), bone mineralization (ash content) and some parameters related to fish condition (heart and liver size). Irrespective of ploidy, at seawater transfer, fish fed the MP diet had significantly highest length and weight and those fed the LP diet significantly lowest length and weight, while those fed the HP diet had intermediate lengths and weights. Increased dietary phosphorus reduced deformities in both ploidies at seawater transfer; however, triploids fed the LP and MP diets had more deformities than diploids fed the respective diets, while there was no ploidy effect observed for fish fed the HP diet. The vertebral bone ash content at seawater transfer was significantly higher in diploids than in triploids when fed the MP diet only. Alkaline phosphatase (ALP) and tartrate‐resistant acid phosphatase (TRACP) enzyme activities and relative gene expression of bone hormones involved in metabolism of plasma phosphate (fgf23) and bone growth (bgp) were not affected by ploidy at seawater transfer, but by dietary P level; LP increased ALP activity and reduced TRACP activity and fgf23 and bgp expression levels in vertebral bone. In scales, LP increased both ALP and TRACP activity. At the termination of the seawater period, the group‐wise pattern in occurrence of vertebral deformities was the same as at seawater transfer. The present results on mortality, growth, bone mineralization and development of skeletal deformities all demonstrate that triploids have a higher P requirement than diploids in fresh water. This study shows that an optimalization of P nutrition for triploid Atlantic salmon can improve health and welfare and reduce down‐grading of triploid salmon.     

Dietary zinc requirement of juvenile grass carp (Ctenopharyngodon idella) based on growth and mineralization

A growth trial was conducted to estimate the optimum requirement of dietary zinc (Zn) for grass carp (Ctenopharyngodon idella). Triplicate groups of grass carp (3.97 ± 0.05 g) were fed diets containing graded levels (13, 25, 34, 53, 89 and 135 mg kg^?1) of Zn for 8 weeks. Grass carp fed with dietary Zn levels higher than 34 mg kg^?1 significantly increased final body weight, weight gain and specific growth rate (P < 0.05). For body composition, fish fed with dietary Zn levels higher than 53 mg kg^?1 significantly decreased the moisture contents but increased the lipid contents of whole body and liver. Whole body, scales, vertebrae and liver mineralization were all affected significantly (P < 0.05) by dietary Zn levels. Zn contents in whole body, scales, vertebrae and plasma were linearly increased up to the 53 mg kg^?1 dietary Zn and then remained stable beyond this level. Grass carp fed with dietary Zn levels higher than 53 mg kg^?1 significantly increased triacyglyceride and total cholesterol contents and plasma alkaline phosphatase activity in plasma (P < 0.05). Broken‐line analysis indicated that 55.1 mg kg^?1 dietary Zn was required for maximal tissue storage and mineralization as well as optimal growth of grass carp.     

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.     

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.     

Optimizing zinc supplementation levels of rainbow trout (Oncorhynchus mykiss) fed practical type fishmeal‐ and plant‐based diets

Rainbow trout (23.1 ± 0.4 g) were fed either a fishmeal‐ or plant‐based diet supplemented with various levels of zinc (0, 15, 30, 60 or 120 mg kg^?1) for 12 weeks. Trout fed the fishmeal diet had significantly higher weight gain than with the plant‐based diet. Zinc supplementation in the fishmeal diet had no effect on growth performance, suggesting that additional dietary supplementation of zinc is not required. However, in trout fed the plant‐based diet, growth increased significantly up to 30 mg kg^?1 zinc after which growth was not affected. Trout fed the plant‐based diet containing no zinc exhibited severe growth retardation, and in fish fed the 0 and 15 mg kg^?1 zinc diets, cataracts were present. Use of broken‐line quadratic modelling suggests that dietary supplementation of zinc needed to prevent deficiency and promote adequate growth in rainbow trout fed the plant‐based diet in this study was 30.1 mg kg^?1 (80 mg kg^?1 total dietary zinc). This is higher than the NRC (2011, Nutrient Requirements of Fish and Shrimp) dietary recommended level of 15 mg kg^?1 for rainbow trout. Following the NRC recommendation could lead to zinc deficiency in rainbow trout fed a plant‐based diet.     

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.     

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.     

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.     

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.     

Dietary vitamin C requirement of juvenile Chinese sucker (Myxocyprinus asiaticus)

An 8‐week growth experiment was conducted to quantify the appropriate dietary vitamin C requirement of juvenile Chinese sucker (Myxocyprinus asiaticus). Triplicate groups of 30 experimental fish [initial body weight: (7.1 ± 0.3) g] were cultured in 500 L aquaria and fed with semi‐purified diets containing six levels [10.1 (unsupplemented diet), 37.4, 64.9, 125.2, 244.2 and 482.0 mg kg^?1 diet, respectively] of vitamin C (supplied as L‐ascorbyl‐2‐polyphosphate). Results showed that weight gain of Chinese sucker was significantly increased with increasing dietary vitamin C levels, but there was no significant difference of weight gain among fish fed the diets containing more than 125.2 mg kg^?1 vitamin C. As dietary vitamin C increased, the liver vitamin C content of fish showed the increasing trend firstly and then stabled, while the muscle vitamin C content significantly increased without reaching a constant level. Lower liver malondialdehyde content was observed in 125.2, 244.2 and 482.0 mg kg^?1 vitamin C groups, and higher antioxidant capacity and superoxide dismutase activities were observed in supplemented groups when compared to the unsupplemented group. Liver aspartate aminotransferase and alkaline phosphatase activities were also significant affected by dietary vitamin C. Ash content of fish fed the diet with 244.2 or 482.0 mg kg^?1 vitamin C was significantly higher than that of fish fed the other diets. However, dietary vitamin C had no significant effects on whole‐body crude protein, lipid and moisture contents. The vitamin C requirement of juvenile Chinese sucker was estimated to be 84.6 and 126.1 mg kg^?1 based on weight gain and liver vitamin C concentration 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.     

Effectiveness of l‐ascorbyl‐2‐polyphosphate as an ascorbic acid source for sea cucumber,Apostichopus japonicus

A feeding trial was conducted to determine the adequate dietary ascorbic acid (AsA) levels and the effects on growth, meat quality and antioxidant status of sea cucumber (10.04 ± 0.06 g), Apostichopus japonicus. l ‐ascorbyl‐2‐polyphosphate (35% AsA equivalent) was supplemented separately to the basal diet to obtain five AsA levels, 0, 598, 1473, 4676 and 14340 mg kg^?1 diet respectively. After 60‐day feeding trial, the sea cucumbers fed diets containing 598 and 1473 mg AsA kg^?1 showed significantly higher (P < 0.05) body weight gain and specific growth rate values than the sea cucumbers fed control diets. The sea cucumbers fed diets containing 1473 and 4676 mg AsA kg^?1 showed significantly higher (P < 0.05) hydroxyproline contents than those of the sea cucumbers fed diets containing 0 and 598 mg AsA kg^?1. Antioxidant enzymes such as total antioxidant capacity, superoxide dismutase and glutathione peroxidase showed increasing trends with the increasing dietary AsA levels, but no significant differences (P > 0.05) were observed when the sea cucumbers fed diets with high dietary AsA levels. The content of malondialdehyde had the opposite trend of antioxidant enzymes. In conclusion, the adequate dietary AsA level focusing on growth performance of sea cucumber is between 598 and 1473 mg kg^?1 diet. Furthermore, high level of dietary AsA (between 598 and 4676 mg kg^?1 diet) improved meat quality and antioxidant status.     

Dietary vitamin E could improve growth performance,lipid peroxidation and non‐specific immune responses for juvenile cobia (Rachycentron canadum)

An 8‐week feeding trial was conducted to establish the dietary vitamin E requirement of juvenile cobia. The basal diet was supplemented with 10, 20, 30, 40, 60, 120 mg vitamin E kg^?1 as all‐rac‐α‐tocopheryl acetate. The results indicated that fish fed the diets supplemented vitamin E had significantly higher specific growth rate, protein efficiency ratio, feed efficiency and survival rate than those fed the basal diet. It was further observed that vitamin E concentrations in liver increased significantly when the dietary vitamin E level increased from 13.2 to 124 mg kg^?1. Fish fed the basal diet had significantly higher thiobarbituric acid‐reactive substances concentrations in liver than those fed the diets supplemented vitamin E. Fish fed the diets supplemented with 45.7 and 61.2 mg kg^?1 vitamin E had significantly higher red blood cell and haemoglobin than those fed the basal diet, while fish fed the diets supplemented with 61.2 and 124 mg kg^?1 vitamin E had higher immunoglobulin concentration than those fish fed the basal diet. Lysozyme and superoxide dismutase were significantly influenced by the dietary vitamin E level. The dietary vitamin E requirement of juvenile cobia was established based on second‐order polynomial regression of weight gain and lysozyme to be 78 or 111 mg all‐rac‐α‐tocopheryl acetate kg^?1 diet, respectively.     

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.     

Interactive effects of dietary magnesium and vitamin E on growth performance,body composition,blood parameters and antioxidant status in Japanese seabass (Lateolabrax japonicus) fed oxidized oil

A study was conducted to investigate effects and interactions of magnesium (Mg) and vitamin E (VE) on growth performance, body composition, hepatic antioxidant capacity and serum biochemistry parameters of juvenile Japanese seabass Lateolabrax japonicus under oxidative stress condition. Fish (initial average body weight of 6.10 ± 0.20 g) were fed 9 oxidized oil diets supplemented with 3 grade levels of Mg (0, 520 and 1570 mg kg^?1 diet) and VE (0, 60 and 200 mg kg^?1 diet) for 8 weeks in freshwater. The results showed that diets supplemented 520 mg kg^?1 Mg and/or 60 mg kg^?1 VE had highest growth and muscle lipid content. There were highest total superoxide dismutase, catalase, glutathione peroxidase activities and lowest malondialdehyde content in liver of fish fed diets supplemented 520 mg kg^?1 Mg and/or 60 mg kg^?1 VE. Contrary to Mg concentrations, Ca concentrations and Ca/Mg ratio in whole body were inversely related to dietary Mg levels. However, combined deficiency or excess of dietary Mg and VE led to the decrease of hepatic antioxidant capacity, body lipid deposition and growth of Japanese seabass under oxidative stress condition.     

Effect of dietary zinc level on growth,enzyme activity and body trace elements of hybrid tilapia,Oreochromis niloticus × O. aureus,fed soya bean meal‐based diets

A feeding experiment was conducted to determine the dietary zinc (Zn) requirement of hybrid tilapia fed on a diet with soya bean meal as the sole protein source. The quantity of phytic acid in the experimental diet was 15.5 g kg^?1. Juvenile hybrid tilapia were fed on diets containing 31–227 mg Zn kg^?1 in triplicates for 6 weeks. Haematology of the fish was not affected by various dietary Zn levels. Fish fed on a diet containing 31 mg kg^?1 endogenous Zn showed the lowest growth rates, feed utilization, and body and plasma Zn levels. Weight gain (WG), plasma Zn level and superoxide dismutase (SOD) activity increased when a higher quantity of dietary Zn of 127 mg kg^?1 was administered to the experimental fish. Beyond this level, the values of these parameters were relatively stable. On the other hand, within the dietary Zn range tested, whole‐body Zn and ash increased with higher dietary Zn levels. Analysis using a broken‐line model showed that the dietary Zn requirements of hybrid tilapia fed on soya bean meal‐based diets containing 15.5 g kg^?1 endogenous phytic acid were 115, 115 and 105 mg kg^?1 based on WG, whole‐body Zn retention and plasma Zn level, respectively.     

Influence of dietary biotin levels on growth and non‐specific immune response in large yellow croaker,Larimichthys crocea R

A 9‐week feeding experiment was conducted to determine the effect of dietary biotin levels on growth performance and non‐specific immune response of large yellow croaker. Fish (6.16 ± 0.09 g) were fed twice daily to apparent satiation with diets containing 0.00 (as the basal diet), 0.01, 0.05, 0.25, 1.24 and 6.22 mg biotin kg^?1 diet. Results showed that fish fed the basal diet had the lowest survival rate, and fish fed 0.05 mg kg^?1 dietary biotin achieved significantly higher final weight and weight gain. Dietary biotin levels had no significant influence on carcass crude lipid, moisture and ash content, but significantly influenced the carcass crude protein. Liver biotin concentration significantly increased with the supplementation of biotin, but no tissue saturation was found within the supplementation scope of biotin. Broken‐line regression analysis of weight gain showed that juvenile large yellow croaker requires a minimum dietary biotin of 0.039 mg kg^?1 for maximal growth. The analyses of serum parameters showed that the moderate‐ (0.05 mg kg^?1) and high‐dose (6.22 mg kg^?1) dietary biotin significantly improved both lysozyme and alternative complement pathway activities, indicating dietary biotin within a certain range could improve the non‐specific immune response of large yellow croaker.     

Dietary astaxanthin levels affect colour,growth, carotenoid digestibility and the accumulation of specific carotenoid esters in the Giant Tiger Shrimp,Penaeus monodon

The carotenoid astaxanthin (Axn) plays a vital role in shrimp pigmentation, with direct influence on product quality, and forms a significant cost component of shrimp aquaculture feeds. However, the effects of dietary Axn on other measures of shrimp physiological performance are varied, and the efficiency of carotenoid uptake from the diet and deposition in shrimp tissues is poorly defined. This study fed juvenile shrimp (Penaeus monodon) diets that contained 0, 25, 50 or 100 mg kg^?1 Axn for 6 weeks. Shrimp fed carotenoid‐free diets had significantly reduced colour and growth than those fed carotenoids, but survival was unaffected. Carotenoid digestibility improved as dietary carotenoid levels increased, and was 98.5% in shrimp fed 100 mg kg^?1 Axn. After 6 weeks, whole body carotenoid levels were significantly depleted in 0 or 25 mg kg^?1 fed shrimp, compared with those fed 50 or 100 mg kg^?1 or compared with initial shrimp. This study also showed that Axn monoesters were enriched with saturated fatty acids, whereas Axn diesters were enriched with monounsaturated and polyunsaturated fatty acids. Combined, these studies demonstrate that a total dietary carotenoid intake of between 25 and 50 mg kg^?1 Axn is required for normal shrimp growth and health in P. monodon. Evidence suggests that there is a functional role for the accumulation of carotenoids and the formation of specific Axn fatty acid esters, and these may be linked to the metabolism, storage, mobilization or deposition of Axn within various tissues.     

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.