Physiological responses of golden mahseer (Tor putitora) fry to dietary zinc and assessment of its optimum requirement

Abstract

Effect of dietary zinc on growth, survival and physiological responses of Tor putitora fry was investigated. A 60-day experiment was conducted with 1,800 fry (avg. wt 54.35 ± 3.09 mg) of golden mahseer distributed randomly among six treatments in triplicate. Six isonitrogenous semi-purified diets were prepared with graded levels of zinc (0, 10, 20, 40, 60 and 80 mg/kg). Zinc sulphate was added as dietary zinc source to the basal diet. Zinc concentration in rearing water was monitored during feeding period and it was set from 0.01 to 0.03 mg/L. Growth parameters as average weight gain, percentage weight gain, feed efficiency ratio were higher (p < 0.05) in fish fed diets with 40 mg Zn/kg. Suppressed growth and higher mortality was observed in groups fed with 80 mg Zn/kg diet. RNA/DNA ratio and whole body zinc retention showed increasing trend with increasing dietary zinc up to 40 mg Zn/kg and plateaued thereafter. Analysis of digestive enzymes revealed that amylase activity increased with increase in dietary zinc levels however, lipase and protease showed rhythmic changes among treatment groups. There was an increasing trend of alkaline phosphatase (ALP) activity with increase in zinc supplementation and highest ALP activity was observed in 80 mg Zn/kg diet which was significantly different from that of control group. Polynomial regression analysis indicated that 44.62–46.73 mg Zn/kg diet is optimum requirement, which favoured enzymatic responses for optimal growth and survivality in T. putitora fry.