Acute Toxicity of Copper to Juvenile Freshwater Prawns, Macrobrachium rosenbergii

Abstract

Copper sulfate is an algicide that is commonly used for phytoplankton and filamentous algae control and has been used as a therapeutant in aquaculture. The objectives of this study were to determine the acute toxicity of copper sulfate and the safe level for use in freshwater prawn, Macrobrachium rosenbergii, production ponds in a high calcium and alkalinity environment. Six concentrations of copper sulfate (0, 0.2, 0.4, 0.6, 0.8, 1.0 mg/L) were tested in 8-L glass aquaria for 48 hours with three replicate aquaria per treatment. Concentrations of calcium hardness and alkalinity were set at 100 mg/L using calcium chloride and sodium bicarbonate, respectively. After 48 hours, survival of the control treatment (0% CuSO₄) averaged 97%, which was significantly higher (P< 0.05) than that of all other treatments. The survival in the 0.2 mg/L and 0.4 mg/L (70% and 73%, respectively) concentrations of CuSO₄ were significantly greater (P< 0.05) than higher dose treatments; but were not significantly different from each other (P> 0.05). Treatments containing 0.6, 0.8, and 1.0-mg/L copper sulfate demonstrated a dramatic decrease in prawn survival, which averaged 30, 7, and 0%, respectively. Regression analysis of the data predicted 48-hour LC₅₀ for copper sulfate tobe0.46 mg/L. Since recommended application rates for use of copper sulfate as an algicide are 1.0 mg/L or more for water with alkalinities of 100 mg/L, copper sulfate treatments are not recommended for prawn production ponds.

Key Words:

• Freshwater prawn
• Macrobrachium rosenbergii
• toxic-ity
• copper