Growth, nutrient retention, wastes output and nonspecific immunity of juvenile snakehead Channa argus in response to dietary zinc levels

Abstract

An 8-week feeding trial was conducted to investigate the effects of dietary zinc levels on growth, nutrient retention, waste output and nonspecific immunity of juvenile snakehead Channa argus. Six isonitrogenous (485 g/kg crude protein) and isolipidic (106 g/kg crude lipid) diets were formulated, with supplementation of graded levels of hydrated zinc sulphate at 0 (diet Zn0), 0.2 (diet Zn0.2), 0.4 (diet Zn0.4), 0.7 (diet Zn0.7), 1.0 (diet Zn1.0) and 1.3 g/kg (diet Zn1.3), which provided the actual dietary zinc concentration of 56, 99, 140, 235, 301 and 375 mg/kg respectively. The highest weight gain rate was found in fish fed diet Zn0.7. Lower feed intake and feed conversion ratio, while higher retention efficiencies of nitrogen and phosphorus, were found in fish fed diets Zn0.2, Zn0.4 and Zn0.7 than in fish fed diets Zn0 and Zn1.3. Zinc retention efficiency decreased with the increase IN dietary zinc levels. Contents of zinc in whole body and spinal bone increased with dietary hydrated zinc sulphate increased from 0 to 0.7 g/kg. Higher nitrogen and phosphorous waste were found in fish fed diets Zn0, Zn1.0 and Zn1.3 than in fish fed diets Zn0.2, Zn0.4 and Zn0.7, and lower zinc waste was found in fish fed diets Zn0, Zn0.2, Zn0.4 and Zn0.7 than in fish fed diets Zn1.0 and Zn1.3. Higher serum C4 and IgM were found in fish fed diets Zn0.7, Zn1.0 and Zn1.3 than in fish fed diet Zn0, Zn0.2 and Zn0.4. Our results showed that dietary supplementation of hydrated zinc sulphate needed to promote fast growth, keep good nutrient retention and immunological capacity, and reduce waste discharge in juvenile snakehead should be 0.7 g/kg (235 mg/kg zinc concentration).