Acute toxicity of ammonia and nitrite to white shrimp Penaeus setiferus postlarvae

Penaeus setiferus postlarvae were exposed to acute levels of ammonia, nitri te, and to a mixture of both by a short-term static method. The 24-h, 48-h and 72-h LC50 values for un-ionized ammonia were 1.49, 1.21 and 1.12 mg/L N H3-N (un-ionized ammonia as nitrogen), and 11.55, 9.38 and 8.69 mg/L ammoni a-N (un-ionized plus ionized ammonia as nitrogen). The 24-h, 48-h and 72-h LC50 values for nitrite were 268.06, 248.84 and 167.33 mg/L nitrite-N (nitr ite as nitrogen). Nitrite was much less toxic than ammonia. The joint effec t of ammonia and nitrite on the postlarvae was synergistic at 48-h exposure and antagonistic after 72 h. Postlarvae of P. setiferus may be considered as organisms sensitive to ammonia and nitrite.