Effects of ammonia on growth and molting of Penaeus monodon juveniles

Abstract

1. Growth of Penaeus monodon juveniles (0.32 ± 0.08 g, 3.92 ± 0.33 cm) exposed to 4, 8 and 20 mg/l ammonia-N (unionized plus ionized ammonia as nitrogen) was significantly lower (P < 0.05) than those exposed to the control treatment after 30 days in 25 ppt seawater at pH 8.05–8.13 and 21.4–25.5°C. 2. The MATC (maximum acceptable toxicant concentration) was 2 mg/l for ammonia-N and 0.11 mg/l for NH3-N (unionized ammonia as nitrogen) after 40 days. 3. Ammonia accelerated molting frequency of the shrimps. The overall intermolt periods of the shrimps exposed to control, 2, 4, 8 and 20 mg/l ammonia-N were 14.20 ± 1.41, 13.21 ± 1.81, 12.48 ± 1.63, 11.54 ± 1.65 and 10.90 ± 1.54 days. 4. Growth of the shrimps which were originally exposed to 2, 4 and 8 mg/l ammonia-N after 60 days recovered after 30 days of exposure to the control solution.