Critical survival rate for all larval stages of penaeid shrimp was determined using static bioassay with copper, cadmium and their I: I mixture. The lethal concentration (24 h LC50) was 200 mg/l of Cu. 250 mg/l of Cd and 300 J.LS'L of mixture in average for all larval stages along with slight variation at every stage (Nauplii- Myses III) in Penaoul monodon LC50 was 400 mg/l. In Penaeul -nicillatul LC,o the values were found to be 200 mg/L of Cu, 230  of Cd and 250 mg/L for mixture in Nauplii to Myses however for postlarvae the LC,o was within the same as in Penaeul monodon. The estimation of survival rate within 24·48 h under lethal and acceptable concentration of copper and cadmium showed culturing farmers at most productive and safe condition of their ponds.