Effect of dietary magnesium supplementation on the growth performance of juvenile gibel carp,Carassius auratus gibelio

Gibel carp (Carassius auratus gibelio) of mean initial weight 3.1 g were fed one of seven casein‐dextrin‐based diets containing graded levels of magnesium (Mg) (39, 120, 220, 380, 700, 1600 and 2900 mg kg^?1) for 3 months with the waterborne Mg concentration of 10.6–12.7 mg L^?1. Magnesium sulphate was used as the supplementation Mg source in the diets. The experiment was carried out in a flow‐through system. Growth, survival rate, Na⁺/K⁺‐ATPase, Mg²⁺‐ATPase and tissue mineral contents were measured to investigate the effect of dietary magnesium in gibel carp. At the end of the experiment, the hepatopancreas of fish were collected for enzyme determination. The hepatopancreas, vertebrae and whole body were collected for tissue magnesium content analysis. After 3 months, dietary magnesium supplementation did not improve the growth performance, including feed intake, weight gain and feed conversion efficiency of juvenile gibel carp. On the contrary, negative impacts on survival, reduced growth performance and dramatically decreased Na⁺/K⁺‐ATPase, Mg²⁺‐ATPase and superoxide dismutase activities were observed in gibel carp fed a high Mg diet of 2900 mg kg^?1. Although serum and hepatopancreas Mg and Ca contents were not affected by dietary Mg supplementation, vertebrae and whole‐body Mg contents increased significantly with the increasing dietary Mg concentrations. Based on the relationship between whole‐body Mg retention and dietary Mg concentration, a suitable dietary Mg level of 745 mg kg^?1 could be estimated for gibel carp. It could be concluded that dietary Mg supplementation did not improve the growth performance, but could increase vertebrae Mg contents of gibel carp. Considering the adverse effects, a dietary Mg concentration of above 2900 mg kg^?1 is not recommended and it should be careful to supplement magnesium in practical diets for gibel carp as most feed ingredients contain high magnesium concentrations.     

Dietary magnesium requirements of juvenile grass carp,Ctenopharyngodon idella

To determine dietary magnesium (Mg) requirements of juvenile grass carp, Ctenopharyngodon idella, magnesium sulphate was added to the basal diet at 0, 150, 300, 600, 1200, 2400 mg Mg kg⁻¹ diet. Each diet was fed to three replicate groups of juvenile grass carp (initial weight: 7.69 ± 0.13 g) in a closed, recirculating rearing system for 76 days. No mortality or nutritional deficiency signs were observed except the growth depression in fish fed the Mg‐deficient diet. Growth performance and activities of serum superoxide dismutase (SOD), glutathione peroxidase (GPx) and lysozyme (LSZ) were highest (P <0.05) in fish fed the diet supplemented with 600 mg Mg kg⁻¹. The serum malondialdehyde (MDA) content was higher (P <0.05) in fish fed the diets supplemented with 0 and 150 mg Mg kg⁻¹ than that in fish fed the diets with ≥300 mg Mg kg⁻¹. Mg concentrations both in whole‐body and vertebrae increased with the increase in dietary Mg level up to 300 mg kg⁻¹, whereupon the response reached a plateau. Analysis by second‐order polynomial regression of weight gain, by broken‐line regression of vertebrae Mg concentration and by linear regression of whole‐body Mg retention of fish indicated that the adequate dietary Mg concentration for juvenile grass carp was 713.5, 627.7 and 469.8 mg kg⁻¹ diet, respectively.     

Dietary magnesium requirement and effects on growth and tissue magnesium content of juvenile grass carp (Ctenopharyngodon idella)

A growth trial was conducted to estimate the optimum concentration of dietary magnesium (Mg) for grass carp (Ctenopharyngodon idella). Triplicate groups of grass carp (5.56 ± 0.02 g) were fed diets containing graded levels (187, 331, 473, 637, 779 and 937 mg kg^?1) of Mg for 8 weeks. Weight gain, specific growth rate and feed efficiency were linearly increased up to 637 mg kg^?1 dietary Mg and then levelled off beyond this level. For body composition, dietary Mg levels higher than 473 mg kg^?1 significantly decreased the moisture content but increased the lipid content of whole body, muscle and liver. Dietary Mg levels higher than 473 mg kg^?1 significantly decreased the ash contents of vertebrae, scales and muscle. Mg contents in whole body, vertebrae, scales and plasma were increased up to 637 mg kg^?1 dietary Mg and then levelled off beyond this level. However, Ca and P contents seem to be inversely related to dietary Mg. Dietary Mg levels higher than 473 mg kg^?1 significantly decreased Zn and Fe contents in whole body and vertebrae. Broken‐line analysis indicated that 687 mg kg^?1 dietary Mg was required for maximal tissue Mg storage, as well as satisfied for the optimal growth.     

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

A growth trial was conducted to estimate the optimum concentration of dietary potassium (K) for grass carp (Ctenopharyngodon idella). Triplicate groups of grass carp (3.96 ± 0.06 g) were fed diets containing graded levels (0.87, 2.90, 5.37, 7.54, 9.87 and 12.4 g kg^?1) of K for 8 weeks. Final body weight, weight gain and feed efficiency and gill Na⁺‐K⁺ ATPase activity were highest in fish fed with 9.87 g kg^?1 dietary K and lowest in fish fed the basal diet (P < 0.05). The K contents in whole body and muscle were linearly increased up to the 9.87 g kg^?1 dietary K and then levelled off beyond this level, whereas in scales and vertebrae up to the 7.54 g kg^?1 dietary K (P < 0.05). However, dietary K levels had no significant effect on ash, Ca, P and Mg contents in whole body, scales, vertebrae or muscle. Analysis using polynomial regression of weight gain and gill Na⁺‐K⁺ ATPase activity and using the broken‐line regression of whole body K concentrations indicated that the adequate dietary K concentration for grass carp is about 9.45–9.99 g kg^?1 diet.     

Growth performance and tissue mineral content of juvenile grouper (Epinephelus coioides) fed diets supplemented with various levels of manganese

This study was conducted to investigate the effect of dietary manganese (Mn) on growth, vertebrae and whole‐body Mn content of juvenile grouper, and to examine the effect of dietary Mn on copper (Cu), iron (Fe), zinc (Zn), calcium (Ca), phosphorus (P) and magnesium (Mg) content of vertebrae and whole body. Seven casein‐gelatin‐based diets were supplemented with 0, 5, 10, 15, 20, 50 and 1000 mg kg^?1 of Mn from MnSO₄·H₂O. Grouper with an initial weight of 12.9 ± 0.4 g were fed to satiation with one of the seven diets for 8 weeks. Growth was not significantly affected by dietary Mn supplements. Vertebrae Mn increased from 31.7 to 118.1 mg kg^?1 dry weight with dietary Mn supplement increasing from 0 to 50 mg kg^?1 (y = ?0.0002x³ + 0.0162x² + 1.3903x + 26.27, R² = 0.9561, where y is the vertebrae Mn content and x is the dietary Mn content). Whole‐body Mn increased from 2.5 to 7.8 mg kg^?1 wet weight with dietary Mn supplement increasing from 0 to 50 mg kg^?1 (y = 0.00001x³ ? 0.00107x² + 0.11054x + 2.24615, R² = 0.9080, where y is the whole‐body Mn content and x is the dietary Mn content). Dietary Mn had no significant effect on vertebrae Fe, Ca, P and Mg content, and whole‐body Cu, Zn and Mg content. However, vertebrae Zn and whole body Ca, P were highest in fish fed diet supplemented with 15 mg kg^?1 of Mn. Based on this, Mn supplement of 15 mg kg^?1 might be the optimum when the basal diet contained 4 mg kg^?1 of Mn. Fish fed diet supplemented with 1000 mg kg^?1 of Mn did not show any gross abnormality or change in feeding behaviour, but Mn contents of vertebrae and whole body were as high as 695.1 mg kg^?1 dry weight and 42.5 mg kg^?1 wet weight, respectively. Also, whole body Fe decreased significantly when Mn supplement was up to 1000 mg kg^?1.     

Dietary magnesium did not affect calcium and phosphorus content in juvenile grouper,Epinephelus coioides

Most of magnesium (Mg) in fish is located in the bone. Dietary calcium (Ca) and phosphorous (P) has been reported to affect scales and vertebrae Mg dramatically in juvenile grouper, but the effect of dietary Mg on tissue Ca and P is unknown. This study was conducted to investigate the effect of dietary Mg supplement on growth, feed efficiency, morphometry, and the ash and Ca, P, sodium (Na) content in scales and vertebrae of juvenile grouper. Seven experimental diets were formulated to contain graded levels of Mg by supplementing the basal diet with 0, 200, 400, 600, 800, 1000 and 2000 mg kg^?1 Mg in the form of Mg sulphate (MgSO₄·7H₂O). Juvenile grouper with an initial body weight of 11.8 ± 0.1 g were fed to apparent satiation twice per day for 10 weeks. Dietary Mg supplement had no significant effect on growth, feed efficiency, and Mg concentration in scales and vertebrae of grouper, which indicates the Mg requirement of grouper was met in fish fed the basal diet. Mg supplements had significant effect on morphometry index such as body length, condition factor, viscera somatic index and mesenteric fat index. Extra dietary Mg supplement to the basal diet had no negative effect on ash, Ca and P concentrations in scales and vertebrae.     

Requirements of vitamin C (L-ascorbyl-2-monophosphate-Mg and L-ascorbyl-2-monophosphate-Na) and its effects on immune responses of grouper, Epinephelus malabaricus

An 8‐week feeding trial was conducted to evaluate two vitamin C derivatives, L‐ascorbyl‐2‐monophosphate‐Mg (C2MP‐Mg) and L‐ascorbyl‐2‐monophosphate‐Na (C2MP‐Na), to satisfy the vitamin C requirement and to test their effects on the immune responses of juvenile grouper, Epinephelus malabaricus. C2MP‐Mg and C2MP‐Na were each supplemented at 20, 50, 80, 150, 250, and 400 mg kg^?1 diet in the basal diet providing of 7, 18, 31, 51, 93, 145 mg ascorbic acid (AA) equivalent of C2MP‐Mg kg^?1 diet and 4, 10, 17, 31, 47, 77 mg ascorbic acid (AA) equivalent of C2MP‐Na kg^?1 diet, respectively. Basal diet without AA supplementation was included as control. Each diet was fed to triplicate groups of grouper (mean initial weight 3.20 ± 0.05 g). Fish fed diets supplemented with either C2MP‐Mg or C2MP‐Na had significantly (P < 0.05) greater weight gain (WG), feed efficiency and survival than those fed the unsupplemented control diet. Liver ascorbate concentrations in fish generally increased as dietary C2MP‐Mg or C2MP‐Na supplementation level increased. Haemolytic complement activity was higher in fish fed diets supplemented with 92 mg AA equivalent of C2MP‐Mg kg^?1 or 10–17 mg AA equivalent of C2MP‐Na kg^?1 than fish fed the unsupplemented control diet. Lysozyme activity was higher in fish fed ≥51 mg AA equivalent of C2MP‐Mg kg^?1 or ≥47 mg AA equivalent of C2MP‐Na kg^?1 than fish fed the unsupplemented control diet. Analysis by broken‐line regression of WG indicated that the adequate dietary vitamin C concentration from each vitamin C derivative in growing grouper is 17.9 mg AA equivalent of 2MP‐Mg kg^?1 and 8.3 mg AA equivalent of C2MP‐Na kg^?1, and it also indicated that C2MP‐Mg is about 46% as effective as C2MP‐Na in meeting the vitamin C requirement of grouper.     

Fluoride retention of Atlantic salmon (Salmo salar) fed krill meal

The present experiment was performed to study how fluoride from krill meal enriched muscle, whole fish and bone of adult Atlantic salmon (Salmo salar) reared in sea water. Atlantic salmon (mean weight 0.5 kg) were divided into four triplicate groups and fed a commercial fish meal based diets with 0, 100, 200 and 300 g krill kg^?1 feed, respectively, for 12 weeks. The fluoride concentrations in the experimental feeds were analysed to be 18, 132, 235 and 358 mg kg^?1, respectively. Growth, mortality and feed efficiency were recorded through the experiment. Fluoride concentration was measured in muscle, whole‐body, and bone initially and after 12 weeks of feeding. The fluoride concentrations in the samples were determined by alkali fusion and fluoride ion‐selective electrode. Growth, mortality and feed efficiency ratio were not affected by the dietary treatments. The results showed that fluoride concentration in muscle, whole body and bone were not affected by the dietary fluoride level. The fluoride concentration in the tissues showed great variation among replicates of the group given the same diet. Fillets of the fish varied between 0.3 and 1.4 mg fluoride kg^?1 wet weight, whereas the whole‐body concentration of fluoride varied between 3.3 and 6.1 mg kg^?1 wet weight and the fluoride bone concentration varied between 5.8 and 7.2 mg kg^?1 fresh weight. These results suggest that Atlantic salmon are highly tolerant of dietary fluoride given as krill meal with concentration of fluoride up to 350 mg kg^?1 diet, and that accumulation of fluoride from feeding diets containing krill meal does not lead to tissue accumulation in the fish, at least over a short period of time.     

Manganese supplementation of a practical, fish meal based diet for Atlantic salmon parr

This experiment was conducted to study whether practical fish meal based feeds for Atlantic salmon, Salmo salar L., require manganese (Mn) supplementation. Three thousand parr of initial weight 4.7 g were randomly distributed into 10 tanks and given a fish meal based diet, either unsupplemented or supplemented with 5, 10, 50 or 100 mg Mn kg^?1 (as MnSO₄*H₂O) for 12 weeks. The basal diet contained 4.8 mg Mn kg^?1. Mn concentration in vertebrae and whole fish responded linearly to supplemented Mn up to a level of 10 mg kg^?1 and then reached a plateau. Dietary Mn supplementation did not affect weight gain, liver Mn concentration, blood haemoglobin concentration or haematocrit. To the practical feed, a supplementary level of 10 mg Mn kg^?1, giving a total Mn concentration of 15 mg kg^?1 diet, was necessary to maintain normal Mn status as determined by Mn level in vertebrae and whole fish. However, taking into account the variable Mn content in fish meal and the uncertainty about availability, we recommend a general supplementation of 15 mg Mn kg^?1.     

Dietary available phosphorus requirement of juvenile grass carp (Ctenopharyngodon idella)

A growth trial was conducted to estimate the optimum concentration of dietary available phosphorus (P) for grass carp (Ctenopharyngodon idella). Triplicate groups of grass carp (5.59 ± 0.02 g) were fed diets containing graded levels (2.36, 4.27, 6.31, 8.36, 10.4 and 14.8 g kg^?1) of available P for 8 weeks. Grass carp fed with the P‐supplemented diets had significantly higher specific growth rate, weight gain, protein efficiency ratio and feed efficiency than fish fed with the basal diet. In whole‐body composition, protein content increased, while lipid content decreased with the increase in P level in diet (P < 0.05). Fish fed with the P‐supplemented diets had significantly higher whole body, vertebrae and scales mineralization (P < 0.05), but Ca/P ratios were not influenced. The blood chemistry analysis showed that dietary available P had distinct effects on P, Ca and Mg contents, as well as on the contents of triacylglycerol and total cholesterol. Broken‐line analysis indicated that 8.49 g kg^?1 dietary available P was required for maximal tissue storage and mineralization as well as optimal growth.     

Growth performance and bone mineralization of large Nile tilapia (Oreochromis niloticus) fed graded levels of available phosphorus

The effect of graded levels of dietary available phosphorus (AP) on large Nile tilapia (145.87 ± 9.51 g) performance, feed efficiency, body composition and mineral retention in vertebrae was evaluated. All male fish were distributed into three replicates in fiberglass aquaria (800 L each; 12 fish per tank) for 87 days and hand fed to pelletized diets three times a day until apparent satiation. Diets with approximately 302 g kg^?1 of digestible protein and 15.2 kJ g^?1 of digestible energy with graded levels of dibasic phosphate yield AP levels of 2.39, 4.17, 6.12 and 8.91 g kg^?1. At the end of the trial, feed intake, hepatosomatic index, fillet yield, whole body moisture and crude protein of fish fed 2.39–8.91 g kg^?1 of AP diets were not significantly different. The supplementation of 6.12 and 8.91 g kg^?1 of AP resulted in significantly increased weight gain, whole body ash and calcium. Whole body crude lipids significantly decreased with increasing AP from 6.12 to 8.91 g kg^?1. However, concentration of zinc in the vertebrae was not affected by dietary treatments. The magnesium contents of the fish vertebrae were lower in fish fed lower dietary AP level. No effects of the dietary AP on apparent digestibility coefficients of energy and nutrients were observed. The study indicated that the dietary AP level of at least 6.12 g kg^?1 satisfies the needs for growth performance, body composition and bone mineralization of large Nile tilapia.     

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 bovine lactoferrin on growth,haematology and non‐specific immune response in rainbow trout (Oncorhynchus mykiss)

The aim of this study was to investigate the effect of dietary lactoferrin (Lf) on growth, haematology and non‐specific immune response of rainbow trout Oncorhynchus mykiss (Walbaum). Fish were fed an experimental diet containing 0 (as control), 50, 100, 200 and 400 mg Lf kg^?1 diet twice daily for 8 weeks and sampled at 2, 4, 6 (immune function and growth), and 8 weeks (immune function, haematology and growth). Statistical analyses revealed no significant effects of dietary Lf on growth performance (specific growth rate, weight gain, feed conversion ratio, feed intake and condition factor) or haematological parameters (red and white blood cell count, haemoglobin, haematocrit, serum iron and total iron binding capacity [TIBC]). Among the serum non‐specific immune parameters, lysozyme activity increased significantly in fish fed 100, 200, or 400 mg Lf kg^?1 feed for 8 weeks, whereas haemolytic complement activity increased in fish fed 100 and 400 mg Lf kg^?1 diet after 6 weeks. The antiprotease activity increased in groups fed 100, 200 or 400 mg Lf kg^?1 diet after 8 weeks. However, no significant effect was observed on serum peroxidase level. It can be concluded that feeding of rainbow trout on the diet supplemented with 100 mg kg^?1 or higher for 8 weeks enhances the non‐specific immune response.     

Dietary phosphorus requirement of GIFT strain of Nile tilapia Oreochromis niloticus reared in freshwater

A study was conducted to estimate the optimum requirement of dietary available phosphorus for GIFT strain of Nile tilapia Oreochromis niloticus. Six purified diets were formulated to contain graded levels (0 (control diet), 2.9, 4.8, 7.6, 9.1 and 10.9 g kg^?1 diet) of available phosphorus. Each diet was fed to triplicate groups of 12 fish with initial average weight (46.03 ± 2.14) g for 8 weeks. The results showed that fish fed the three lowest phosphorus diets (0, 2.9 and 4.8 g kg^?1) had significantly lower weight gain rate, specific growth rate (SGR) and feed efficiency than those fed the other diets (P < 0.05). The survival rate of fish fed the control diet was significantly lower than that of the fish fed the other diets (P < 0.05). Whole body viscerosomatic index and crude lipid content decreased significantly with increasing dietary available phosphorus levels (P < 0.05), while the contents of crude ash, calcium, phosphorus in the whole body and vertebrae showed the opposite trend (P < 0.05). The blood chemistry analysis showed that dietary available phosphorus had significant effects on serum phosphorus concentration, enzyme activities of alkaline phosphatase and parathyroid hormone level. Quadratic curve analysis based on SGR indicated that the minimum dietary requirement of available phosphorus for maintaining optimal growth of tilapia was 8.6 g kg^?1.     

Dietary calcium requirement and effects on growth and tissue calcium content of juvenile grass carp (Ctenopharyngodon idella)

A growth trial was conducted to estimate the optimum concentration of dietary calcium (Ca) for grass carp (Ctenopharyngodon idella). Triplicate groups of grass carp (4.52 ± 0.02 g) were fed diets containing graded levels (2.75, 4.51, 6.24, 7.99, 9.66 and 11.5 g kg^?1) of Ca for 8 weeks. Weight gain, feed efficiency and protein efficiency ratio were linearly increased up to the 7.99 g kg^?1 dietary Ca and then maintained stable beyond this level (P < 0.05). Dietary Ca levels higher than 7.99 g kg^?1 significantly increased the ash contents of whole body, vertebrae and scales. Ca contents in whole body, vertebrae and scales were linearly increased up to the 7.99 g kg^?1 dietary Ca and then maintained stable beyond this level (P < 0.05). In contrast, dietary Ca levels higher than 9.66 g kg^?1 significantly decreased Mg contents in whole body, vertebrae and scales. Dietary Ca levels higher than 7.99 g kg^?1 significantly increased plasma alkaline phosphatase activity. However, plasma Ca, P and Mg contents were not significantly affected by dietary Ca supplements (P > 0.05). Polynomial regression analysis indicated that 10.4 g kg^?1 dietary Ca was required for maximal tissue storage and mineralization as well as optimal growth.     

Dietary selenium requirement for juvenile cobia,Rachycentron canadum L.

A 10‐week feeding trial was conducted to estimate the optimum dietary selenium (Se) requirement for juvenile cobia, Rachycentron canadum L. The basal diet was formulated to contain 50.6% crude protein from vitamin‐free casein, gelatin. A control diet (no added seleno‐dl ‐methionine) and five experimental diets containing 0.20, 0.40, 0.60, 0.80 and 1.00 mg seleno‐dl ‐methionine kg^?1 were prepared. Each diet was randomly fed to triplicate groups of juvenile cobia with initial weight 6.27±0.03 g in a flow‐through system. The Se concentration in rearing water was monitored during the feeding period, and was not detectable. The dietary Se level significantly influenced the survival, specific growth rate (SGR), feed efficiency and the Se concentrations in the whole body and vertebra of cobia. The Se‐dependent glutathione peroxidase (EC 1.11.119) activity increased with an increase in the dietary Se levels (P<0.05). Hepatic glutathione reductase (EC 1.6.4.2) activity was the highest in fish fed the diet with 0.21 mg Se kg^?1, and declined with an increase in the dietary Se levels. Based on broke‐line regression of SGR, the Se concentration in the whole body and vertebra, the Se requirements of juvenile cobia were 0.788, 0.811 and 0.793 mg Se kg^?1 diet in the form of seleno‐dl ‐methionine respectively.     

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.     

Effect of various levels of lipid exchanged with dextrin at different protein level in diet on growth and body composition of juvenile flounder Paralichthys olivaceus

A 3 × 3 factorial experiment was conducted to determine proper levels of dietary protein, lipid and dextrin for juvenile flounder. Nine experimental diets were formulated to contain three protein levels (410, 460 and 510 g kg^?1) and three lipid levels (60, 130 and 190 g kg^?1) with corresponding dextrin levels (250, 150 and 50 g kg^?1). Triplicate groups of fish (8.9 ± 0.4 g) were hand‐fed the diets to apparent satiation for 7 weeks in flow‐through system. Specific growth rate was the highest in fish fed the 510 g kg^?1 protein diet with 60 g kg^?1 lipid, and was not significantly different from that of fish fed 460 g kg^?1 protein diet with 60 g kg^?1 lipid. Feed efficiency ratio tended to increase as dietary protein level increased. The feed efficiency ratio of fish fed the 510 g kg^?1 protein diets with 60–190 g kg^?1 lipid levels was not significantly different from that of fish fed 460 g kg^?1 protein diet with 60 g kg^?1 lipid. Daily feed intake tended to decrease with increasing dietary lipid level at each protein level. Daily protein intake increased with increasing dietary protein level at 60 g kg^?1 lipid level. Hepatosomatic index and visceralsomatic index increased with increasing dietary lipid level at each protein level. The lipid contents of liver, viscera and whole body, and concentrations of plasma total cholesterol and triglyceride increased with increasing dietary lipid levels; however, no significant difference was observed in the contents of dorsal muscle lipid. The results of this study suggest that the diet containing 460–510 g kg^?1 protein with low lipid level (60 g kg^?1) is optimal for growth and efficient feed utilization of juvenile flounder.     

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.     

Dietary biotin requirement for growth of juvenile zebrafish Danio rerio (Hamilton‐Buchanan)

This study was conducted to estimate the dietary biotin requirement for maximum growth of zebrafish Danio rerio. Six isonitrogenous and isocaloric purified diets containing 0.031 (biotin‐unsupplemented diet), 0.061, 0.263, 0.514, 1.741 and 2.640 mg biotin kg^?1 diet were fed in triplicate tanks for a total of 12 weeks to juvenile zebrafish (initial mean body mass 0.13 ± 0.001 g). From 4 weeks of feeding, fish fed diets with ≤0.061 mg biotin kg^?1 showed biotin deficiency signs, such as retarded growth and skeletal deformity, was observed on some dead fish. At the end of the study, gill disorders were observed on some fish and liver glycogen accumulation were also observed in fish fed these diets. Fish fed the biotin‐unsupplemented diet exhibited a lower final body weight, protein efficiency ratio and feed utilization than the fish fed the biotin‐supplemented diets, whereas the highest values were observed with the diet containing 0.51 mg biotin kg^?1 diet (P < 0.05). A linear relationship (r² = 0.77; P < 0.0001) was observed between whole‐body biotin content and dietary biotin level. A broken‐line analysis indicated that the optimum dietary biotin content for maximal growth expressed as final body weight is 0.51 mg kg^?1 diet.