Joint Action of Ammonia and Nitrite on Tiger Prawn Penaeus monodon Postlarvae

Tiger prawn Penaeus monodon postlarvae (PL6) were exposed to a mixture of ammonia and nitrite by the static renewal method. When the toxicity ratio of the ammonia-nitrite mixture was 1:1, the 48 h, 72 h and 96 h LC50 values were 2.20, 1.43 and 0.84 toxicity units which were equivalent to 12.66 mg/L ammonia-N (0.60 mg/L NH₃-N) plus 14.91 mg/L nitrite-N, 8.23 mg/L ammonia-N (0.39 mg/L NH₃-N) plus 9.69 mg/L nitrite-N, and 4.83 mg/L ammonia-N (0.23 mg/ L NH₃-N) plus 5.69 mg/L nitrite-N. When the toxicity ratio of the ammonia-nitrite mixture was 51, the 48 h, 72 h and 96 h LC50 values were 2.50, 1.56 and 0.85 toxicity units which were equivalent to 23.98 mg/L ammonia-N (1.13 mg/L NH₃-N) plus 5.65 mg/L nitrite-N; 14.96 mg/L ammonia-N (0.71 mg/L NH₃-N) plus 3.52 mg/L nitrite-N, and 8.15 mg/L ammonia-N (0.39 mg/ L NH, N) plus 1.92 mg/L nitrite-N. A mixture of ammonia and nitrite exerted greater toxicity than high concentrations of either ammonia or nitrite alone. The combined effect of ammonia and nitrite on P. monodon postlarvae was antagonistic for 48 and 72 hours exposure, but synergistic after 96 hours exposure.     

Osmolality and ion balance in giant river prawn Macrobrachium rosenbergii subjected to changes in salinity: role of sex

Haemolymph osmolality, chloride and sodium concentrations of giant river prawn Macrobrachium rosenbergii adults were determined 15 days after they were transferred from freshwater to 0 (control), 7, 14 and 21‰ salinity. Haemolymph osmolality, chloride and sodium concentrations of prawns transferred to 7, 14 and 21‰ reached a constant level within 0.5, 2 and 3 days respectively. Both male and female adults exhibited strongly hyper‐osmotic and hyper‐ionic over the range of 0–14‰. The isosmotic point was 14.5 and 15.6‰, the iso‐ionic point of chloride was 14.5 and 14.7‰, and the iso‐ionic point of sodium was 16.5 and 15.7‰ for males and females respectively. The adults lost their hyper‐regulatory ability and became osmo‐conformic over the media of 14.5–21‰ and 15.6–21‰ and ion‐conformic with respect to sodium over the media of 16.5–21‰ and 15.7–21‰ for males and females respectively. The adults displayed hypo‐ionic to the media at 21‰ with respect to chloride.