EFFECTS OF NITRITE ON GROWTH AND MOLTING OF PENAEUS-MONODON JUVENILES

1. Survival of Penaeus monodon juveniles (1.40 +/- 0.05 g; 6.30 +/- 0.07 cm) reared in control, 2, 4, 8 and 20 mg/l nitrite-N by a static renewal method after 80 days was 100, 100, 96.7, 86.7 and 70%, respectively. 2. Growth of the shrimps reared at 4, 8 and 20 mgl/l nitrite-N was significantly lower (P < 0.05) than control animals and those reared at 2 mg/l nitrite-N after 20 days. 3. EC50 (concentration that reduced growth by 50% of that of the controls) for weight gain was 17.41 and 22.45 mg/l nitrite-N, and EC50 for length increase was 16.14 and 26.20 mg/l nitrite-N after 20, and 60 days, respectively. 4. Nitrite decreased the ratio of carapace length to total length, and enhanced molting frequency of the shrimps. Average molting frequency of shrimps reared as control and at 2, 4, 8 and 20 mg/l nitrite-N was 6.27, 6.30, 6.34, 6.92 and 7.14 times, respectively. 5. The MATC (maximum acceptable toxicant concentration) was estimated to be 2 mg/l nitrite-N from the growth and molting.