Effects of temperature on acute toxicity of ammonia to Penaeus semisulcatus juveniles

Abstract

Penaeus semisulcatus juveniles (1.6±0.2 g) were exposed to different concentrations of ammonia-N in a series of acute toxicity tests by the semi-static method at four different water temperatures (14, 18, 22 and 26 °C) at pH of 8.2 and 39 ppt salinity. The mortality rate increased with increasing concentrations of ammonia and exposure time. Low temperatures clearly increased tolerance of the shrimps to total ammonia-nitrogen (TAN) and un-ionised ammonia (NH 3-N). The 24-, 48-, 72- and 96-h LC 50 values of TAN were 92.22, 76.56, 64.07 and 55.84 mg l −1 at 14 °C; 57.00, 46.07, 41.85 and 36.01 mg l −1 at 18 °C; 41.10, 33.42, 30.61 and 26.72 mg l −1 at 22 °C; and 25.89, 15.44, 13.44 and 11.44 mg l −1 at 26 °C, respectively. The 24-, 48-, 72- and 96-h LC 50 values of NH 3-N were 3.18, 2.64, 2.22 and 1.92 mg l −1 at 14 °C; 2.94, 2.37, 2.15 and 1.85 mg l −1 at 18 °C; 2.77, 2.25, 2.06 and 1.80 mg l −1 at 22 °C; and 2.26, 1.35, 1.17 and 1.00 mg l −1 at 26 °C, respectively. The safe level for rearing P. semisulcatus was estimated to be 5.6, 3.6, 2.7 and 1.1 mg l −1 for TAN and 0.19, 0.19, 0.18 and 0.10 mg l −1 for NH 3-N at 14, 18, 22 and 26 °C water temperatures, respectively. The safe level was fivefold higher for TAN and twofold higher for NH 3-N at 14 °C in comparison to 26 °C.