Effect of dietary copper on the hepatic concentration and subcellular distribution of copper and zinc in the rainbow trout ( Salmo gairdneri)

Abstract

Feeding trials were conducted with six groups of rainbow trout (mean initial weight of 35 g) using purified diets with an estimated gross energy of 1442 kJ 100 g and copper contents ranging from 3.5 to 1000 mg Cu/kg diet. With the exception of groups 1 and 2 (given 102 and 194 mg Cu/kg), which showed an atypical growth response, the weight gain and feed conversion were reduced with increasing levels of Cu in the diet. No gross pathologies and very low mortalities were noted even in the group receiving the highest dietary copper level. Copper and zinc were determined in freeze-dried samples and in subcellular fractions from individual trout livers using atomic absorption spectrophotometry. A linear relationship was observed between liver copper concentration and copper provided in the diet. Copper intake had no effect on hepatic zinc concentration. Increased dietary copper also gave increased copper levels in whole fish but the concentration factor was much lower than in the liver. The relative retention of copper given at levels above 100 mg Cu/kg dry diet was low and was estimated to be 1.3%. Subcellular fractionation studies demonstrated that 43–67% and 36–49%, respectively, of hepatic copper and zinc were sedimented with the fractions nuclei, mitochondria and lysosomes. Increased dietary levels of copper had apparently no effect on the subcellular distribution of zinc except at the highest level (group 6) where an increase in zinc recovered in the nuclear fraction was observed.