Influence of dietary phosphorus levels on growth,body composition,metabolic response and antioxidant capacity of juvenile snakehead (Channa argus × Channa maculata)

A study was conducted to estimate the optimum requirement of dietary phosphorus (P) for Channa argus × Channa maculata. Effects of dietary P levels on the tissue composition, serum biochemical parameters and antioxidant status were also examined. Five practical diets were formulated to contain graded levels (4.8 g kg^?1, 6.4 g kg^?1, 7.9 g kg^?1, 9.4 g kg^?1 and 11.0 g kg^?1) of available P from dietary ingredients and monocalcium phosphate (MCP). Each diet was randomly assigned to triplicate groups of 30 juvenile fish (initial body weight, 20.50 ± 0.53 g) for 8 weeks. The results showed that the specific growth rate (SGR) and weight gain (WG) were all significantly improved by dietary P up to 9.4 g kg^?1 (P < 0.05) and then levelled off beyond this level. Broken‐line analysis showed maximum weight gain (WG) was obtained at dietary available P concentrations of 9.6 g kg^?1. With the increase in dietary P level, protein efficiency rate (PER) increased significantly and reached a plateau, while the feed conversion ratio (FCR), the mesenteric lipid somatic index (MSI) and the whole‐body lipid content significantly reduced (P < 0.05). Dietary P levels also affected the mineralization (ash and P) of whole body, vertebrae and scale (P < 0.05). Quadratic analysis based on P contents in whole body, vertebrae, scale and ash content in vertebra indicated that the available P requirements were 10.4, 9.8, 10.0 and 10.3 g kg^?1, respectively. However, no differences were found in the whole‐body moisture, crude protein, serum calcium (Ca) contents or Ca/P value, as well as the viscerosomatic index (VSI) and hepatosomatic index (HSI) among all the treatments (P > 0.05). Triglyceride (TG), total cholesterol (TC), high‐density lipoprotein cholesterol (HDL‐C) and low‐density lipoprotein cholesterol (LDL‐C) decreased significantly, while serum P content, HDL‐C/TC and HDL‐C/LDL‐C value increased significantly with dietary available P levels (P < 0.05). No significant changes in superoxide dismutase activity and malondialdehyde (MDA) content were observed (P > 0.05), but serum catalase (CAT) and glutathione peroxidase (GPx) activities and the ratio of CAT/SOD and GPx/SOD increased significantly with increasing dietary P levels (P < 0.05). In conclusion, the optimal P requirement of juvenile snakehead in practical feed was 9.6 g kg^?1. Signs of P deficiency were characterized by poor growth, slightly reduced mineralization and the antioxidant capacity and an increase in body lipid content.     

Effects of dietary phosphorus on growth,body composition and immunity of young taimen Hucho taimen (Pallas, 1773)

The effects of dietary phosphorus (P) on growth, body composition and immunity of young taimen (Hucho taimen) were studied. Six purified diets contained graded levels (2.3‐control, 4.0, 5.6, 7.5, 9.1 and 10.8 g kg^?1 diet) of available P. Each diet was fed to triplicate groups of 30 fish with an initial average weight (55.31 ± 0.38) g for 84 days. The weight gain, specific growth rate and feed conversion ratio were improved by dietary available P up to 4.35 g kg^?1 (P < 0.05) and then levelled off. Hepatosomatic index and body crude lipid content decreased significantly with increasing P levels, while ash contents and P concentrations in the whole body and vertebrae increased by dietary available P up to 4.36 and 4.44 g kg^?1 and then levelled off respectively (P < 0.05). Liver superoxide dismutase and glutathione peroxidase and plasma alkaline phosphatase activities in the treatment groups were significantly higher compared with the control group (P < 0.05). Plasma IgM contents increased linearly with increasing dietary P from 4.0 to 9.1 g kg^?1 group and then decreased. Dietary P supplementation reduced plasma triglyceride, malondialdehyde and liver malondialdehyde contents. There were no significant effects on plasma total protein, albumin, globulin, glucose, aspartate aminotransferase and alanine aminotransferase, catalase, lysozyme and liver catalase compared with the control group (P > 0.05). Broken line regression analysis indicated that dietary available P requirement was 4.34 and 4.35 g kg^?1, based on weight gain and P concentration in the whole body respectively.     

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 available phosphorus requirement of juvenile walking catfish,Clarias leather

A feeding trial was conducted to evaluate the optimum requirement of dietary available phosphorus (AP) for juvenile walking catfish, Clarias leather. Six practical diets were formulated to contain graded levels (2.2, 3.9, 5.5, 7.1, 8.8 and 10.4 g kg^?1) of AP from dietary ingredients and monocalcium phosphate. Each diet was randomly fed to triplicate groups of fish with initial mean weight of 7.94 ± 0.08 g in floating cages (1.5 × 1.5 × 2.0 m) suspended in an earthen pond, and each cage was stocked initially with 60 fish. Fish were fed thrice daily (07:30, 13:00 and 17:30) to apparent satiation for 10 weeks. Both specific growth rate (SGR) and protein efficiency ratio significantly increased with increasing AP from 2.2 to 5.5 g kg^?1 (P < 0.05) and then levelled off. Dietary AP levels significantly influenced whole‐body protein, lipid and ash contents as well as condition factor and hepatosomatic index (P < 0.05). Whole‐body and vertebrae phosphorus contents showed similar patterns as SGR in response to dietary AP content. Broken‐line analyses based on SGR, phosphorus contents in the vertebrae and whole‐body indicated the AP requirements were 5.8, 7.2 and 7.5 g kg^?1, respectively.     

Growth,body composition,intestinal enzyme activities and microflora of juvenile Jian carp (Cyprinus carpio var. Jian) fed graded levels of dietary phosphorus

A 9‐week feeding trial was carried out with juvenile Jian carp (Cyprinus carpio var. Jian) to study the effects of dietary phosphorus on growth, body composition, intestinal enzyme activities and microflora. Quadruple groups of juvenile Jian carp (7.17 ± 0.01 g) were fed practical diets containing available phosphorus 1.7 (unsupplemented control), 3.6, 5.5, 7.3, 9.2 and 11.0 g kg^?1 diet to satiation. Feed intake, specific growth ratio and feed efficiency were the lowest in fish fed the basal diet (P < 0.05). Body moisture, protein, lipid content and ash were all significantly affected by dietary available phosphorus levels (P < 0.05). Activities of trypsin, amylase, Na⁺, K⁺‐ATPase, alkaline phosphatase and gamma‐glutamyl transpeptidase were improved with increasing dietary phosphorus levels. Intestinal Aeromonas and Escherichia coli decreased with increasing dietary phosphorus up to 3.6 and 5.5 g kg^?1 diet respectively (P < 0.05), while Lactobacillus increased with the increasing dietary phosphorus up to 9.2 g kg^?1 diet (P < 0.05). These results suggested that phosphorus could enhance intestinal enzyme activities of juvenile Jian carp and the minimum dietary available phosphorus requirement for SGR of juvenile Jian carp (7.2–63.8 g) was 5.2 g kg^?1 diet.     

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

A nine‐week feeding experiment was conducted in flow‐through system with gibel carp (43.8 ± 0.2 g) to study the effects of dietary available phosphorus (P) on growth, phosphorous digestibility and intestinal enzyme activities. Seven semipurified diets were formulated to contain 0.8 (the basal), 2.4, 3.6, 6.1, 7.4, 10.1 and 15.8 g available phosphorus kg^?1 diet. The results showed that specific growth rate and feed efficiency increased with increasing dietary available P from 0.8 to 7.4 g P kg^?1. Fish body ash increased with increasing dietary available P, while moisture, protein content or energy content had no difference. Total phosphorus waste discharging (TPW) increased with increased dietary phosphorous. Plasma glucose was higher in the fish fed with 7.4 g kg^?1 P. Plasma triglycerides was lower in fish fed diets containing 6.1–10.1 g kg^?1 P. No significant effects were observed in plasma P and Ca (p > .05). The activities of intestinal amylase, lipase and trypsin showed no difference, while AKP and Na⁺, K⁺‐ATPase activities decreased with increasing dietary available P. In conclusion, based on the regression between specific growth rate (SGR), P retention efficiency, feed efficiency (FE) and dietary available P, the available P requirements for on‐growing gibel carp were 10.69, 8.22 and 6.72 g kg^?1, respectively.     

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.     

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.     

Effect of dietary protein levels on growth performance and whole body composition of summerling and winterling spotted barbel (Hemibarbus maculates Bleeker)

Six test diets with protein levels varying from 250 to 500 g kg^?1 were fed to six triplicate groups of summerling (initial weight: 1.56 g) and seven test diets with protein levels varying from 200 to 500 g kg^?1 were fed to seven triplicate groups of winterling (initial weight: 9.49 g) for 8 weeks. Weight gain (WG) and feed efficiency (FE) of summerling significantly increased with increasing dietary protein levels from 250 to 350 g kg^?1 and slightly declined, but without statistical significance at a dietary protein level of 400 g kg^?1, then further significantly decreased with increasing protein levels to 450 and 500 g kg^?1; WG of winterling increased significantly with increasing dietary protein levels from 200 to 300 g kg^?1 (P < 0.05), and above this level, WG had a tendency to decrease with increasing dietary protein levels. Winterling fed diets with 300 and 400 g kg^?1 of dietary protein had significantly higher FE than those fed other diets. WG data analysis by quadratic regressions showed that the optimum dietary protein levels required for the maximum growth of summerling and winterling were 374 and 355 g kg^?1 of dry diet respectively. Protein efficiency ratio of both summerling and winterling negatively correlated with levels of dietary protein. The whole body moisture, protein, lipid and ash of summerling after being fed various test diets for 8 weeks were significantly different among treatments (P < 0.05). The whole body moisture and fat of winterling were also significantly affected by dietary protein levels (P < 0.05), while the whole body protein and ash of winterling were not (P > 0.05).     

Optimal dietary methionine requirement of juvenile Chinese sucker,Myxocyprinus asiaticus

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

Dietary inorganic phosphorus or microbial phytase supplementation improves growth,nutrient utilization and phosphorus mineralization of juvenile red sea bream,Pagrus major,fed soybean‐based diets

A 2 × 3 factorial design with triplicates examined the interaction between dietary inorganic phosphorus (IP) and phytase on growth, mineral utilization and phosphorus (P) mineralization in juvenile red sea bream. The treatments were three levels of dietary IP supplementation at 0, 2.5 and 5 g kg^?1, either without or with phytase supplementation [2000 FTU kg^?1; phytase unit is defined as the amount of enzyme activity which liberates 1 micromol of inorganic phosphorus per minute at pH 5.5 and 37 °C at a substrate concentration (sodium phytate) of 5.1 mmol L^?1]. Juvenile red sea bream (IBW = 1.3 g ± 0.1) were stocked twelve fish per tank and fed for 50 days. Growth and feed efficiency were significantly (P < 0.05) enhanced by both dietary P and phytase supplementation. Feed intake and survival rate were not significantly affected by the dietary treatments. Both dietary IP and phytase supplementation significantly increased plasma IP and Mg levels. Concentration of vertebral mineral and scale P was significantly increased by both dietary treatments. A skeletal malformation syndrome of scoliosis occurred in fish fed both non‐IP and non‐phytase supplemented diet. Interaction between main dietary effects was detected for vertebral Zn, scale P and whole‐body ash and Mg content. With regard to growth and other examined productivity traits, phosphorus requirement of juvenile red sea bream can be met if supplemented with 2000 FTU phytase kg^?1 or in the absence of phytase, by dietary inclusion of 2.5–5 g kg^?1 of IP.     

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.     

Effects of dietary protein to energy ratios on growth and body composition of juvenile Chinese sucker,Myxocyprinus asiaticus

A growth experiment was conducted to investigate effect of dietary protein to energy ratios on growth and body composition of juvenile Myxocyprinus asiaticus (initial mean weight: 10.04 ± 0.53 g, mean ± SD). Nine practical diets were formulated to contain three protein levels (340, 390 and 440 g kg^?1), each with three lipid levels (60, 100 and 140 g kg^?1), in order to produce a range of P/E ratios (from 22.4 to 32.8 mg protein kJ^?1). Each diet was randomly assigned to triplicate groups of 20 fish in 400‐L indoors flow‐through circular fibre glass tanks provided with sand‐filtered aerated freshwater. The results showed that the growth was significantly affected by dietary P/E ratio (P < 0.05). Fish fed the diets with 440 g kg^?1 protein (100 and 140 g kg^?1 lipid, P/E ratio of 31.43 and 29.22 mg protein kJ^?1) had the highest specific growth rates (SGR) (2.16 and 2.27% day^?1, respectively). However, fish fed the diet with 390 g kg^?1 protein and 140 g kg^?1 lipid showed comparable growth (2.01% day^?1), and had higher protein efficiency ratio (PER), protein productive value (PPV) and energy retention (ER) than other groups (P < 0.05). No significant differences in survival were found among dietary treatments. Carcass lipid content was positively correlated with dietary lipid level, but irrespective of protein level and inversely correlated with carcass moisture content. Carcass protein contents increased with increasing dietary lipid at each protein level. The white muscle and liver composition showed that lipid increased with increasing dietary lipid level (P < 0.05). Dietary protein concentrations had significant effect on condition factor (CF), hepatosomatic index (HSI) and viscerosomatic index (VSI) (P < 0.05). However, dietary lipid concentrations had no significant effect on CF, HSI (P > 0.05). Based on these observations, 440 g kg^?1 protein with lipid from 100 to 140 g kg^?1 (P/E ratio of 29.22 to 31.43 mg protein kJ^?1) seemed to meet minimum requirement for optimal growth and feed utilization, and lipid could cause protein‐sparing effect in diets for juvenile Chinese sucker.     

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 histidine requirement of fingerling Indian major carp, Cirrhinus mrigala (Hamilton)

An 8‐week growth trial was conducted to determine the dietary histidine requirement of the Indian major carp, Cirrhinus mrigala fingerling (length 4.22 ± 0.45 cm; weight 0.61 ± 0.08 g; n = 40). Isonitrogenous (400 g kg^?1 crude protein) and isoenergetic (17.90 kJ g^?1 gross energy) diets with graded levels of l ‐histidine (2.5, 5.0, 7.5, 10.0, 12.5 and 15.0 g kg^?1 dry diet) were formulated using casein and gelatin as a source of intact protein, supplemented with l ‐crystalline amino acids. Twenty fish were randomly stocked in 70‐L indoor polyvinyl circular fish tank (water volume 55‐L, water exchange rate 1–1.5 L min^?1) and fed experimental diets at the rate of 5% of their body weight/day divided over two feedings at 08:00 and 16:00 h. Maximum live weight gain (295%), best feed conversion ratio (FCR) (1.48) and protein efficiency ratio (PER) (1.69) occurred at 7.5 g kg^?1 of dietary histidine level. When live weight gain, FCR and PER data were analysed using second‐degree polynomial regression, the break points indicated histidine requirements at 9.4, 8.6 and 8.5 g kg^?1 of dry diet respectively. Significantly (P < 0.05) higher whole body protein and low moisture values were recorded at 7.5 g kg^?1 histidine level. Body fat increased significantly (P < 0.05) with increasing histidine levels. However, at 7.5 and 10 g kg^?1 histidine diets body fat did not differ (P > 0.05) to each other. Ash content of fish fed diets containing various levels of histidine did not differ except at 2.5 and 5.0 g kg^?1 inclusion levels where significantly (P < 0.05) higher ash was recorded. Protein deposition was also found to be significantly (P < 0.05) higher in the 7.5 g kg^?1 histidine diet. Based on the polynomial regression analysis of FCR and PER data, it is recommended that the diet for fingerling C. mrigala should contain histidine at 8.5 g kg^?1 of dry diet, corresponding to 21.25 g kg^?1 of dietary protein for optimum growth and efficient utilization of feed.     

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

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

Performance,body compositions,input and output of nitrogen and phosphorus in Siberian sturgeon,Acipenser baerii Brandt,as affected by dietary animal protein blend replacing fishmeal and protein levels

An 8‐week growth trial was conducted using a 2 × 3 factorial design to evaluate the effect of substitution of fishmeal (FM) by rendered animal protein blend [APB, comprised of 400 g kg^?1 poultry by‐product meal, 350 g kg^?1 meat and bone meal, 200 g kg^?1 hydrolysed feather meal (HFM) and 50 g kg^?1 spray‐dried blood meal] in diets of Siberian sturgeon, Acipenser baerii Brandt. Two isoenergetic control diets were formulated to contain two different protein levels [high‐protein control (400 g kg^?1), with 483 g kg^?1 of FM] and [low‐protein control (360 g kg^?1), with 400 g kg^?1 of FM]. At each protein level, dietary FM protein was replaced by APB at 75% and 100% levels and supplemented with crystallized essential amino acid under ideal protein concept. The six diets were named as HC, HAPB75, HAPB100, LC, LAPB75 and LAPB100, respectively. No significant differences were found in weight gain rate (WGR) and specific growth rate (SGR), but fish fed with the low‐protein diets showed higher feed intake and feed conversion ratio. Plasma growth hormone and insulin‐like growth factors I of each group were not significantly different (P > 0.05). The whole‐body composition and liver composition were not affected by dietary protein levels, replacement or their interaction. Muscle protein and lipid contents of fish fed with diet LAPB100 were significantly lower than those of HC group. Digestibility of nitrogen (N) and phosphorus (P) were reduced with higher APB inclusion levels, but productive N and P values of all groups were not different. Lower N and P intake induced lower nutrients losses (P < 0.05). The results suggested that dietary protein level could be reduced to 360 g kg^?1 from 400 g kg^?1 without affecting WGR or SGR and significantly reduced nutrients lose. Furthermore, dietary FM protein can be totally replaced by APB in feed formulation either at 400 g kg^?1 or at 360 g kg^?1 protein level.