Toxicity of Copper Sulfate to Largemouth Bass Fry in Naturally Soft Water

Abstract The use of copper sulfate pentahydrate (herein, designated CuSO 4 ) for fungus control on fish embryos is extremely effective and economical for farmers in waters with moderate or high alkalinity/hardness; however, fry toxicity in low alkalinity/hardness waters is a concern. The present study determined the acute toxicity of CuSO 4 to Largemouth Bass Micropterus salmoides in naturally soft water (42 mg/L alkalinity [as CaCO 3 ], 41 mg/L hardness [as CaCO 3 ]). Median lethal concentration (LC50) values at 24 h were 3.97 mg/L CuSO 4 for yolk‐sac fry and 5.24 mg/L CuSO 4 for swim‐up fry. Most importantly for farmers, the no observed effect concentration (NOEC; the highest concentration tested to not cause fry mortality) was 0.625 mg/L CuSO 4 for both stages of fry. Regarding the safe use of CuSO 4 for fungus control on Largemouth Bass embryos, this research was done to demonstrate CuSO 4 toxicity to Largemouth Bass fry in soft water.