TOXICITY OF AMMONIA TO THE LARVAE OF PENAEUS INDICUS H. MILNE EDWARDS

Abstract

Short-term experiments revealed a progressive increase in tolerance of the larval stages of Penaeus indicus to ammonia. 24-h LC30 values for nauplius, protozoea and mysis were 3.58 mg ammonia N/l (0.29 mg NH3-N/I), 17.86 mg ammonia- Nil (0.95 mg NHyN) and 46.01 mg ammonia-Nil O.lTmgNHj-N/I). respectively. 48-h LCjo value for protozoea was 16.8 mg ammonia-N per liter (1.18 mg NH3-N/I. Long-term chronic-toxicity experiments on nauplius to postlarva-1 showed that the 9-day incipient LCjo was 11.99 ppm of ammonia-N{l (0.93 ppm NH3-N). The ECjo (the concentration at which the percentage of larvae that metamorphosed to postlarvae was reduced to 50% of that of the controls) for ammonia was 3.23 ppm ammonia-N11 (0.25 ppm NH3-N). Safe level of ammonia that should be maintained in the sea water used for larval rearing was calculated on the basis of incipient LC50 value as 1.2 mg ammonia-N/! or 0.093 ppm NH3-N/I. More sensitive estimate of safe level based on EC 50 value was 0.32 ppm ammonia-N|! or 0. 25 ppm NH3-N.