A proposed method to diagnose acute copper poisoning in cultured rainbow trout, ( Oncorhynchus mykiss)

Abstract

Seventy rainbow trouts were exposed to lethal copper conditions using water-borne copper, in order to assess the diagnosis value of copper accumulation and its ratio to other essential metals. Poisoned fish showed a copper increase in some organs, but these changes did not always indicate significant differences versus control fish. Metal/copper ratios showed higher variations than did copper concentrations. In fact, significant decreases of Zn/Cu ratios were observed in tissues which did not show significant differences for copper. When experimental results were compared to copper and copper/metal ratios in different Spanish rainbow trout farms, individual variations between exposed and unexposed fish were observed. All unexposed animals showed gill Zn/Cu ratios higher than 0.5, and 90% higher than 1.5; while 93% of poisoned fish showed gill Zn/Cu ratios lower than 1.5, and 84% lower than 0.5. Similar findings were observed for opercle. Therefore, we propose gill and opercle Zn/Cu ratios to be considered as a possible method to diagnose acute copper poisoning in farmed rainbow trout.