Effects of copper levels in diets high in plant ingredients on gilthead sea bream (Sparus aurata) fingerlings

Abstract

Fish meal is increasingly substituted in diets for gilthead sea bream with ingredients of terrestrial origin which may affect the mineral content and availability. Among these minerals, copper (Cu) is an essential trace element whose excess may have a potential toxic effect. Since ingredients of terrestrial origin have higher Cu levels than marine ones it is important to define the optimal dietary supply of Cu. Therefore, the aim of this study was to evaluate optimal dietary inclusion level of Cu in low FM-FO diets for gilthead sea bream fingerlings.Five practical diets with low FM (10%) and FO (6%) contents were respectively supplemented with 5 levels of CuSO4 to provide 5.5, 7.4, 9.3, 11.0 and 32.0 mg Cu kg−1 diet. Sea bream fingerlings (12.6 ± 1.4 g, mean ± SD) were distributed in 15 tanks with 30 fish per tank in triplicates and randomly assigned one of the dietary treatments. The fish were fed three times a day until apparent visual satiation for 42 days. Growth was recorded at the end of the trial and samples were taken for biochemical, mineral, histology, X-ray and hepatic gene expression analyses.The results obtained suggest that gilthead sea bream fed practical diets based on plant protein sources that provide at least 5.5 mg Cu kg−1 need no additional Cu supplementation, whereas dietary contents of 11–32 mg Cu kg−1 negatively affected gilthead sea bream performance by reducing growth, increasing oxidative risk and inducing hepatic damage and cholestasis.Dietary Cu levels did not affect body weight, SGR, TGC or FCR, denoting that the level in the non-supplemented diet (5.5 mg Cu kg−1) was enough to cover the requirements for growth. However, increasing dietary Cu levels from 5.5 to 9.3 mg/kg-1 up-regulated cat gene expression. On the contrary elevation of dietary Cu levels up to 11.0 and 32.0 mg Cu kg−1 tended to reduce growth and increased liver steatosis, broken cell margin, peripheral nuclei and sinusoid dilatation which are the markers of hepatic damage and cholestasis denoting potential toxic effects of Cu.