The 24 hr, 48 hr, 72 hr and 96 hr LC50 values for CuSO4.5H2O in Macrobrachium rosenbergii were 0.60, 0.55, 0.45 and 0.35 mg L-1, respectively (Fig.1). A regression analysis of prawn survival (%) on Cu2+ concentration was highly significant (P < 0.001; r2 = 0.979). Using the resulting regression equation, the 72-hr LC50 for Cu2+ was calculated to be 0.45 mgL-1, while, it was 0.35 mgL-1 for 96-hr