Requirement of rainbow trout for dietary zinc.

Abstract

The requirement of rainbow trout for dietary zinc was investigated by feeding them with diets containing graded levels of zinc. The results of the present study demonstrate that zinc is an essential trace element in the diet of rainbow trout, even though rearing water contains a low concentration of this element (11μg/ι). The fish fed a diet low in zinc content (lppm) showed an extremely low growth rate and high mortality. A large number of the fish on the zinc-deficient diet were found to suffer from cataracts in the eyes and erosion of the fins and of the skin. The dietary zinc levels also influenced the digestibility of protein and carbohydrate, especially that of protein. The proximate composition of the fish body and the contents of trace elements in the various organs varied according to the dietary zinc levels. Judging from the growth rate of the fish, an adequate zinc content of the diet of rainbow trout was estimated to be 15 to 30ppm.