Toxicity of chlorine to different sizes of black tiger shrimp (Penaeus monodon) in low-salinity shrimp pond water

An experiment was conducted, in a dark room with controlled temperature (27.3-28.4degreesC), to determine the acute toxicity of chlorine concentration to black tiger shrimp (Penaeus monodon fabicus) of sizes 0.02 g, 2.75 g, 8.47 g and 23.65 g. Toxicity tests on each of these shrimp sizes were run in triplicate in glass jars under static conditions without media renewal. The concentration of active chlorine that killed 50% of the shrimp of each size after 24-h exposure (LC50-24 h) was used as an indicator of acute toxicity. Chlorine concentrations applied in the shrimp toxicity test ranged from 2.0 to 14.5 mg L-1 in shrimp pond water. As the test water contained total suspended solids of 22.0-85.0 mg L-1 and total ammonia nitrogen of 0.18-0.40 mg L-1, the resultant concentrations of combined residual chlorine ranged from 0.6 to 3.5 mg L-1, which were the effective doses causing shrimp mortality. The test results showed that 24-h LC50 for average shrimp size at 0.02, 2.75, 8.47 and 23.65 g occurred in water containing combined residual chlorine at a concentration of 0.91,1.39,1.74 and 1.98 mg L-1, for which the original application doses were 6.96,2.05 11.50 and 13.34 mg L-1 respectively.