Anchovy oil is a very suitable supplementary ingredient for fish feeds due to the essential fatty acid composition. The acute toxicity of zinc and copper ions for rainbow trout (Oncorhynchus mykiss Walbaum 1792) were evaluated by static bioassays. The average weight and lenght of fish used in the zinc experiments were 3,02 ±0.21 g and 6.52 ±0.12 cm, respectively, while the tests with copper ions were performed with larger fish (7.12 ±0.60 g and 7.89 ±0.12 cm). Temperature, dissolved O2, pH and ammonia were measured daily, and the average values were 14.62 ±0.41ºC, 7.49 ±0.15 mg/l O2, 7.48 ±0.12 and 0.013 ±0.002 mg/l NH3-N, respectively (total hardness of 249.6 mg/l CaCO3). Chemically pure salts of zinc chloride (ZnCl2) and copper sulphate (CuSO4 5H2O) dissolved in distilled water were used as toxicants. Eight zinc ion concentrations with a control group and 8 copper ion concentrations with a control group were prepared. The LT50 (lethality time for 50%) and 96-h LC50 (lethal concentration for 50%) values were calculated. The LC50 values of zinc and copper ions for rainbow trout were found to be 12.88 and 0.094 mg/l, respectively. Survival time decreased with increasing concentrations of zinc and copper ions. Copper ion concentrations were found to be more toxic than zinc ion concentrations for rainbow trout.
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