| Vitamin E and phosphorus play important roles in the development of fish. Diets with proper vitamin E and phospholipid can improve the growth performance, immunity and antioxidant ability of fish, while improper addition of vitamin E or phosphorus will have a disadvantage effect on fish growth, even cause fish deformities. Hybrid snakehead is an important economic fish in China. At present, scarce information is available about its relevant nutritional research, which constrains the development of its culture. Therefore, our study, with hybrid snakehead(Channa argus ×Channa maculata) as an object, was conducted to evaluate the effects of dietary vitamin E and phosphorus on the growth, body composition, antioxidant ability and serum biochemical indexes of fish in order to determine the proper additive amount of vitamin E and phosphorus and provide references for the formulation of hybrid snakehead feed.1. Effects of dietary vitamin E on growth performance and antioxidant status in juvenile hybrid Snakehead(Channa argus × Channa maculata)An 8-week feeding trial was conducted to investigate the effects of dietary vitamin E on growth performance, vitamin E concentration in tissue and antioxidant status of juvenile snakehead. The snakeheads were fed with five isonitrogenous and isoenergetic experimental diets that contained 13(control), 52, 79,168 and 326 mg of vitamin E/kg respectively. The results showed that the special growth rate increased significantly with increasing dietary vitamin E from 13 to 79 mg /kg, and then leveled off(P<0.05). No significant differences were found in protein efficiency ratio(PER), feed conversion ratio(FCR), feed intake(FI) and survival(SR) of fish among all groups(P>0.05). Vitamin E supplementation appeared to improve hepatic glutathione peroxidase(GSH-Px) activity significantly. A consistent decline in the hepatic and serum malondialdehyde(MDA) content was observed in fish fed diets with the increased supplementation of vitamin E(P<0.05). In addition, with the increasing level of vitamin E, serum alanine aminotransferase(ALT) and aspartate aminotransferase(AST) were reduced(P<0.05). However, serum superoxide dismutase(SOD), catalase(CAT) and alkaline phosphatase(ALP) activity were enhanced in fish fed 79 mg vitamin E kg-1 diet, and then decreased significantly as the content of vitamin E in the diet increas(P<0.05)ed. Meanwhile, serum albumin(ALB) and globulin(GLOB) were not affected by the supplemental levels of dietary vitamin E(P>0.05). The vitamin E concentrations in liver and serum increased significantly with increasing dietary vitamin E(P<0.05).In conclusion, the present study indicated that the dietary appropriate vitamin E could enhance the growth performance, antioxidant status and non-specific immune response. Based on the broken-line regression analysis of SGR, the optimum vitamin E supplemental level in the diet is estimated to be 80.5 mg/kg for Channa argus × Channa maculata. Influence of dietary phosphorus levels on growth,body composition, metabolic response and antioxidant capacity of juvenile snakehead(Channa argus × Channa maculata)2. 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 leveled 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 of 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 difference 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.
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