The Requirement and Toxicity of Selenium in Rainbow Trout (Salmo Gairdneri)

Abstract

This study measured the dietary selenium requirement of rainbow trout and their response to excessive levels of dietary selenium. A dietary selenium level of 0.07 µg/g dry feed with a waterborne selenium level of 0.4 ± 0.2 µg/liter and a dietary vitamin E level of 0.4 IU/g dry diet was sufficient to prevent frank selenium deficiency symptoms. Maximal plasma GSH.px activity was obtained at a dietary selenium level between 0.15 and 0.38 µg/g dry feed which is less than the average selenium concentration of commercial diets. Chronic dietary selenium toxicity occurred at 13 µg selenium/g dry feed. Major effects of selenium toxicity were reduced growth rate, poor feed efficiency and a high number of mortalities. No histopathological lesions or significant deviation in the investigated blood parameters or liver somatic index were detected in trout raised on diets containing 13 µg selenium/g dry feed. Tissue selenium analysis indicated that trout can maintain homeostasis with dietary selenium levels up to 1.25 µg/g dry feed. The selenium uptake and accumulation in tissues of trout reared on diets containing in excess of 3 µg/g dry feed may ultimately be toxic to trout if maintained over long periods of time.