EFFECTS OF AMMONIA ON GROWTH AND MOLTING OF PENAEUS-JAPONICUS JUVENILES

Mortality of Penaeus japonicus juveniles (1.23 +/- 0.09 g) exposed to control levels, and to 5, 10, 20 and 30 mg/l ammonia-N (NH3-N + NH4+-N), using the static renewal method in 34 ppt sea water at pH 8.21 and 25.5-degrees-C after 60 days was 0, 6.7, 26.7, 70.0 and 86.7%, respectively. Growth of the shrimps exposed to 10, 20 and 30 mg/l ammonia-N was significantly lower (P<0.05) than in controls after 40 days. Percentage weight gain and percentage length increase were 125 (control), 90, 70, 43, 39; and 28 (control), 22, 18, 14, 11, respectively, at 5, 10, 20 and 30 mg/l ammonia-N after 60 days. Ammonia affected reduction of weight more than length. The 60-day EC50 (concentration that reduced growth by 50% of that of the controls) for weight gain was 19.88 mg/l ammonia-N (1.39 mg/l NH3-N), and 60-day EC50 for length increase was 23.86 mg/l ammonia-N (1.67 mg/l NH3-N). The MATC (maximum acceptable toxicant concentration) for 30 and 50 days was 5 mg/l and less than 5 mg/l for ammonia-N (0.35 mg/l and less than 0.35 mg/l for NH3-N). Ammonia increased the molting frequency of the shrimps. The 1st-2nd intermolt period of the shrimps exposed as controls and to 5, 10, 20 and 30 mg/l ammonia-N was 21.9, 19.2, 17.7, 14.6 and 10.3 days, respectively.