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.     

Selection of marine species and meals for cephalopod feeding based on their essential mineral composition

A quantitative analysis of the essential mineral content (mg kg^?1 dry weight) was carried out in 31 samples, including molluscs, crustaceans, fish and meals in an attempt to identify those most suitable for formulating cephalopod diets. The mineral ratios (MR: content in the test sample/content in whole Octopus vulgaris) were used as index of nutritional quality. Both crustaceans and oysters presented an optimal profile that covered the macro‐ and microelements composition of O. vulgaris. These samples differed from the rest by their higher Ca, Mg, B, Cu and Zn contents based on a principal component analysis. Fish were deficient in macroelements, such as Na (MR: 70–420 g kg^?1) and Mg (MR: 220–690 g kg^?1), but would be good source of K, Ca and P. Most fish were also deficient in Fe, Zn and Cu, although the copper content would be the most affected (MR: 3–130 g kg^?1). Fish and krill meals showed a high content of Ca and P, although both would be deficient in Na (MR: 440–470 g kg^?1) and Cu (130–540 g kg^?1), along with K, Fe and Zn in krill and Mg and B in fish. Among the plant meals, sunflower and soybean were the most appropriate, presenting higher total content of minerals and MRs above 1000 g kg^?1 for all minerals, except Na, Cu and Zn.     

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 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.     

Supplemental graded levels of neutral phytase using pretreatment and spraying methods in the diet of grass carp,Ctenopharyngodon idellus

A feeding trial was conducted for 8 weeks to evaluate the effects of graded levels of neutral phytase supplementation using pretreatment or spraying method on growth performance, body composition, bone mineral content and serum biochemical parameter in grass carp, Ctenopharyngodon idellus. A control diet without phytase was added and six additional diets were arranged as a 2 × 3 factorial with two methods (pretreatment or spraying) and three levels of phytase (500, 1000 or 1500 U kg^?1). The results showed that supplemental phytase at different levels in the diet and with different application methods all improved weight gain, specific growth rate and protein efficiency ratio of grass carp (P < 0.05). The feed conversion ratio in phytase‐supplemented groups was lower than the control. Dietary phytase addition reduced the lipid content in the whole body of grass carp. Phytase supplementation with different method increased ash and mineral (P, Ca, Mg and Zn) contents in whole‐body and vertebra (P < 0.05). The increase in these mineral contents was also observed in the serum. Based on the results, we may conclude that: 1) supplemental dietary phytase, regardless of the application methodology, improved the growth performance and nutrient utilization in grass carp; 2) the pretreatment mode of phytase application was more effective than spraying at the same phytase level.     

Effects of dietary calcium levels on growth and tissue mineralization in Japanese seabass,Lateolabrax japonicus

A feeding trial was conducted to investigate the effects of different levels of calcium (Ca) on growth and tissue mineralization in Japanese seabass, Lateolabrax japonicus. Six experimental diets were formulated to contain different levels of Ca (2.9, 4.2, 6.5, 7.9, 10.2 and 31.0 g kg^?1) from dietary ingredients and Ca‐lactate·5H₂O. The diets were fed to three triplicate groups of Japanese seabass (initial weight, 12.5 ± 0.0 g) for 56 days. Dietary Ca had no significant effect on survival or feed efficiency; however, the highest Ca (31.0 g kg^?1) diet significantly reduced weight gain, feeding rate and whole‐body and muscle protein and lipid contents, as well as serum Ca concentration and alkaline phosphatase activity. A significant reduction in vertebral Ca, P, Zn, Fe and Mn contents and scale Ca, P, Mg and Mn contents was observed in Japanese seabass as dietary Ca level increased. Deformed fish were primarily found in the 2.9 and 31.0 g Ca kg^?1 groups, indicating that these fish had poor bone mineralization.     

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.     

Total aromatic amino acid requirement of juvenile grass carp (Ctenopharyngodon idella)

This experiment was conducted to investigate total aromatic amino acid requirement of juvenile grass carp Ctenopharyngodon idella. Six isonitrogenous and isoenergetic semipurified diets containing casein and gelatin with graded level of phenylalanine (7.8, 11.1, 14.4, 17.6, 21.7, 24.9 g kg^?1 DM) were formulated. Each diet was randomly assigned to triplicate group of 30 fish (3.58 ± 0.002 g, mean ± SEM) each tank for 8 weeks. The highest weight gain (WG, %), final body weight (g) and specific growth rate were recorded when phenylalanine level was 17.6 g kg^?1 of the diet. Fish muscle protein content, protein efficiency ratio (PER), feed conversion ratio and alanine aminotransferase were significantly affected by dietary phenylalanine level. The polynomial regression calculated using WG and PER indicated that the optimal dietary total aromatic amino acid (phenylalanine + tyrosine) requirement for juvenile grass carp was 24.4 g kg^?1 of the diet, corresponding to 65.9 g kg^?1 of dietary protein.     

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.     

Effects of dietary phenylalanine on growth,digestive and brush border enzyme activities and antioxidant capacity in the hepatopancreas and intestine of young grass carp (Ctenopharyngodon idella)

This study investigated the effects of phenylalanine on growth, digestive and absorptive ability and antioxidant status of young grass carp (Ctenopharyngodon idella). Young grass carp were fed diets containing 3.4 (basal diet), 6.1, 9.1, 11.5, 14.0 and 16.8 g phenylalanine kg^?1 diet with a fixed of 10.7 g tyrosine kg^?1 diet for 8 weeks. Percent weight gain (PWG), feed efficiency and feed intake of fish were the lowest in fish fed the basal diet (P < 0.05). Trypsin, lipase and amylase activities in the hepatopancreas, and antioxidants including glutathione contents and glutathione reducase activities in the hepatopancreas and intestine were all the highest in fish fed 11.5 g phenylalanine kg^?1 diet (P < 0.05). Trypsin, chymotrypsin and amylase activities in whole intestine, and creatine kinase, Na⁺, K⁺‐ATPase and alkaline phosphatase activities in the proximal intestine, and superoxide dismutase activities in the hepatopancreas and intestine were all the highest when phenylalanine at level of 9.1 g kg^?1 diet (P < 0.05). In conclusion, phenylalanine improved growth, digestive and absorptive ability, and antioxidant capacity of young grass carp. The phenylalanine requirement of young grass carp (256–629 g) based on PWG was 10.4 g kg^?1 diet or 3.44 g 100 g^?1 protein.     

Effects of replacing soybean meal with faba bean meal on growth,feed utilization and antioxidant status of juvenile grass carp,Ctenopharyngodon idella

A 56‐day feeding trial was conducted to evaluate the potential use of faba bean meal (FBM) as a partial replacement of soybean meal (SBM) in the commercial diets for juvenile grass carp (Ctenopharyngodon idella) with initial average weight of 3.39 ± 0.03 g. Five isonitrogenous and isoenergetic diets were formulated to replace SBM by FBM protein at 0, 150, 300, 450 and 600 g kg^?1 (designated as FBM0, FBM15, FBM30, FBM45 and FBM60, respectively). The results indicated that up to 420.3 g kg^?1 of FBM can be used for grass carp without negative effects on growth and feed utilization. The higher FBM level would result in growth retardation. The apparent digestibility and intestinal enzymes activities significantly decreased with increased dietary FBM, and the lowest value was observed in diet FBM60. No significant differences were detected in protein contents of whole body, muscle and liver tissues among all treatments. Intraperitoneal fat index and lipid contents of whole body and liver tissues significantly decreased with increased dietary FBM. Serum antioxidant enzymes were significantly affected by dietary FBM level, and the lowest enzymes activities were found in diets FBM45 and FBM60. Results of this study indicated that FBM can successfully replace SBM protein in the commercial diets for grass carp, and the optimum level of SBM replacement with FBM was 450 g kg^?1 on the basis of the maximum growth gain.     

The impaired flesh quality by iron deficiency and excess is associated with increasing oxidative damage and decreasing antioxidant capacity in the muscle of young grass carp (Ctenopharyngodon idellus)

To investigate effects of iron (Fe) on growth, haematological parameters, flesh quality and antioxidant status in muscle, young grass carp (Ctenopharyngodon idella) (292.0 ± 3.2 g) were fed graded levels of Fe (20.7, 38.4, 52.8, 79.3, 98.0 and 120.0 mg kg^?1 diet) for 8 weeks. Per cent weight gain (PWG) and feed intake were improved with Fe levels up to 52.8 mg kg^?1 diet. Serum Fe, erythrocyte counts, haemoglobin (Hb), haematocrit and mean cell haemoglobin increased with optimal Fe levels (38.4–79.3 mg kg^?1 diet) (P < 0.05). The muscle protein and lipid contents were increased by dietary Fe, whereas moisture, liquid loss, shear force and hydroxyproline contents followed opposite trends. Malondialdehyde and protein carbonyl contents in muscle were the lowest in fish fed the 52.8 or 79.3 mg Fe kg^?1 diet, respectively, while superoxide dismutase, catalase, glutathione‐S‐transferase, glutathione peroxidase and glutathione reductase activities, and glutathione content were increased by Fe levels up to 52.8–79.3 mg kg^?1 diet. Results indicated that the optimal Fe improved growth, flesh quality and muscle antioxidant defence of young grass carp. Dietary Fe requirements for PWG, serum Fe and Hb of young grass carp (292–695 g) were 73.5, 72.8 and 69.0 mg kg^?1 diet, respectively.     

Effects of dietary cellulase addition on growth performance,nutrient digestibility and digestive enzyme activities of juvenile crucian carp Carassius auratus

This study was conducted to determine the effects of dietary cellulase addition on improving the nutritive value of Chlorella for juvenile crucian carp Carassius auratus (initial body weight: 2.99 ± 0.02 g, mean ± SEM). Five isonitrogenous and isoenergetic experimental diets were formulated to contain 0.0 (control), 0.5, 1.0, 1.5 and 2.0 g kg^?1 cellulase, respectively. Each experimental diet was randomly assigned to triplicate groups with 25 juvenile fish per fibreglass tank for 8 weeks. The results showed that weight gain, specific growth rate, feed intake and the trypsin activity in the anterior intestine increased with increasing dietary cellulase to 1.5 g kg^?1 and then declined with further addition. However, the mRNA expression levels of Mrf4 and Myf5, the apparent digestibility coefficients for dry matter, protein, energy and the majority of amino acids, and the activity of lipase in the anterior intestine were highest in fish fed the 1.0 g kg^?1 cellulase diet, and then tended to decline with further cellulase supplementation. In conclusion, the optimal dietary cellulase supplementation level was 1.0–1.5 g kg^?1, which can improve growth performance, digestive activities and nutrient digestibility in crucian carp.     

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.     

Carbohydrate utilization by herbivorous and omnivorous freshwater fish species: a comparative study on gibel carp (Carassius auratus gibelio. var CAS III) and grass carp (Ctenopharyngodon idellus)

Two 8‐week feeding trials were conducted to evaluate dietary carbohydrate utilization by omnivorous gibel carp (Carassius auratus gibelio) (2.4 ± 0.1 g) and herbivorous grass carp (Ctenopharyngodon idellus) (6.5 ± 0.1 g). Five isonitrogenous (370 g kg^?1) and isolipid (70 g kg^?1) diets were formulated with increasing corn starch levels (60, 140, 220, 300 and 380 g kg^?1). Results showed that specific growth rate (SGR), feed efficiency (FE) and protein retention efficiency (PRE) of gibel carp significantly increased from dietary starch of 60 to 300 g kg^?1 and then decreased from 300 to 380 g kg^?1, but those of grass carp showed no significant differences between treatments. Independent of dietary starch levels, grass carp gained significantly higher FE and PRE than gibel carp. Feeding rate (FR) of gibel carp was significantly higher than that of grass carp. In two fish species, high dietary starch (300 and 380 g kg^?1) tended to obtain higher hepatosomatic index (HSI), serum triglyceride, hepatic lipid and body lipid contents. Serum glucose concentration of grass carp was not affected, while that of gibel carp fed the starch of 300 g kg^?1 diet was significantly lower than those of the fish fed other four diets (60, 140, 220 and 380 g kg^?1). Grass carp showed high tolerance to dietary starch while dietary corn starch should be no more than 300 g kg^?1 for gibel carp. High starch contents may cause lipid accumulation in the liver and body.     

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.     

Phytase and sodium diformate supplementation in a plant‐based diet improves protein and mineral utilization in rainbow trout (Oncorhynchus mykiss)

A basal isonitrogenous and isoenergetic plant‐based diet (Control) was supplemented with either 10 g kg^?1 sodium diformate (NaDF), 4000 FTU kg^?1 phytase (Phy) or a combination of both additives (NaDF + Phy). Three hundred juvenile rainbow trout with an average weight of 120 g were randomly distributed into 12 fibreglass tanks (300 L). After 65 days of trial, fish fed diets containing phytase, NaDF or the combination of both additives showed a higher growth rate (P < 0.05) compared to fish fed Control diet. NaDF increased feed intake (P = 0.032), while phytase inclusion resulted in a better feed conversion ratio (P < 0.0001) and a higher N retention efficiency (P = 0.02) compared with the Control. Apparent digestibility of P, Ca, Mg and Zn was improved by the use of phytase (P < 0.005) as well as P, Ca and Mg retention efficiency in fish (P < 0.0001). Using 4000 FTU kg^?1 phytase in plant‐based diets resulted in a 13% and 50% reduction in N and P loadings, respectively. The use of NaDF in combination with phytase in a plant‐based diet for rainbow trout resulted in a higher weight gain than that when NaDF was used alone.     

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

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

Comparative studies on dietary protein requirements of juvenile and on‐growing gibel carp (Carassius auratus gibelio) based on fishmeal‐free diets

Two trials were conducted to investigate protein requirements of juvenile (3.18 g in Trial 1) and on‐growing (87.1 g in Trial 2) gibel carp, Carassius auratus gibelio var. CAS III. Six isoenergetic diets containing 250–500 g kg^?1 dietary protein were formulated using soy protein concentrate (SPC) and casein as protein sources. The results showed that weight gain (WG) increased when dietary protein increased from 250 to 400 g kg^?1 and decreased at 400 to 500 g kg^?1 CP in Trial 1, while WG increased when dietary protein increased from 250 to 350 g kg^?1 and kept constant at 350 to 500 g kg^?1 CP in Trial 2. With increasing dietary protein, feed conversion ratio (FCR) decreased, while protein retention efficiency (PRE) decreased in Trial 1 and was not affected in Trial 2. Apparent digestibility coefficient of protein (ADC_p) increased with increasing dietary protein in two trails. Trypsin activity increased with dietary protein in the juveniles and was not affected in on‐growing fish. Hepatic alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities increased with dietary protein. Broken‐line and quadratic regression of WG estimated that dietary protein requirements for maximum growth were about 402–427 g kg^?1 for the juvenile and 337–418 g kg^?1 for on‐growing gibel carp.     

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.