Lethal effects of ammonia and nitrite on Penaeus chinensis juveniles

Abstract

Juveniles of the prawnPenaeus chinensis (3.96 ±0.18 cm, 0.36±0.06 g) reared in Taiwan in 1989 were exposed to different concentrations of ammonia and nitrite, by a static renewal method in 33‰ seawater at pH 7.94 and at 26 °C. The 24, 48, 96 and 120 h LC50 (median lethal concentration) of ammonia were 3.29, 2.10, 1.53 and 1.44 mg l−1 for NH3-N (un-ionized ammonia as nitrogen) and 79.97, 51.14, 37.00 and 35.09 mg l−1 for ammonia-N (un-ionized plus ionized ammonia as nitrogen). The 24, 96, 120, 144 and 192 h LC50 of nitrite-N were 339, 37.71, 29.18, 26.98 and 22.95 mg l−1. The LC50 decreased with increasing exposure time. During the first 96 h,P. chinesis juveniles were more susceptible to ammonia than nitrite. However, prawns were less tolerant to nitrite than ammonia when exposed for more than 96 h. The “threshold” was found at 120 and 192 h for ammonia and nitrite, respectively, on the toxicity curves. “Incipient LC50” was 1.44 mg l−1 for NH3-N, 35.09 mg l−1 for ammonia-N and 22.95 mg l−1 for nitrite-N. The “safe value” forP. chinensis juveniles was 0.14, 3.51 and 2.30 mg l−1, respectively.