Zinc supplementation and its effect on thermal stress resistance in Carassius auratus fry

Abstract

Goldfish (Carassius auratus) fry (80 mg) were fed purified diets based on casein as a protein source and containing different levels of supplementary zinc (0, 30, 60, 90, 120, 150 mg Zn/kg diet) for nine weeks. There were overt signs of zinc deficiency (suppressed growth, high mortality) in fish fed the zinc-deficient control diet, while the highest growth was obtained in fish fed the 60 mg Zn/kg diet. Alkaline phosphatase (ALP) activity in the muscle and super-oxide dismutase (SOD) activity in the liver were highest in fish fed the 60 mg Zn/kg diet and did not significantly improve beyond this level. Muscle and whole body zinc concentrations increased proportionately with the dietary zinc supplementation but iron and copper concentrations in fish tissue were not affected by the supplementary zinc. After the 9-week trial, twelve fish were subjected to thermal stress (28-32°C) for another four weeks to observe growth and the physiological response of the stress enzyme, SOD. After thermal stress, growth improved with the increase in zinc. Likewise, SOD activity in the fish liver increased, indicating that fish utilize more zinc in high temperatures to counteract stress.