Alcaraz, G., Chiappa, X., Espinoza, V., Vanegas, C.
Abstract:
The white shrimp Penaeus setiferus is a potential species for culture in the coast of the Gulf of Mexico; however some aspects need to be studied before P. setiferus culture may be achieved. Although in marine systems ammonia and nitrite are often present in low levels, under marine culture conditions these inorganic nitrogenous compounds may accumulate. Ammonia and nitrite are the most common pollutants in culture systems, and their toxicity has been demonstrated in penaeid shrimps. The goals of this study were to determine the lethal median concentrations (24, 48 and 72-h LC50) of ammonia and nitrite, and the effect of both pollutant and their mixture on the thermal tolerance of the white shrimp postlarvae.
White shrimp postlarvae were acutely exposed to ammonia, to nitrite, and to a mixture of both pollutants, by short-term static method. The 24, 48 and 72-h LC50 of ammonia were 1.38, 1.20 and 1.10 mg/1 NH3-N. Shrimp postlarvae were especially sensitive to ammonia after 24-h of exposure. Nitrite was several times less toxic than ammonia; the 24, 48 and 72-h LC50 of nitrite were 267.3, 172.8 and 172.8 mg/1 NO2-N. The joint effect of ammonia and nitrite was antagonic at 48 h of exposure. In all ammonia-nitrite combinations the mixtures were less toxic than single nitrite exposure. In contrast, the mixture was more toxic than ammonia when evaluated alone.
The Critical Thermal Maximum (CTM) method was used to determine the acute effect of ammonia, nitrite and the combined effect of both toxicants on the thermal tolerance of Penaeus setiferus postlarvae. Ammonia did not affect the temperature response of shrimp. Nitrite exposure significantly decreased temperature tolerance of postlarvae. CO-exposure to ammonia-nitrite mixture modified the CTM; an inverse relationship between nitrite/ammonia ratio concentrations and the CTM was observed. The results suggest that exposure to these nitrogenous compounds decreased the ability of white shrimp postlarvae to tolerate additional thermal stress. White shrimp postlarvae may be described as sensitive organisms to nitrogenous compounds.
(Laboratorio de Ecofisiologia, Departamento de Biologia, Facultad de Ciencias, Universidad Nacional Autonoma de Mexico, Mexico D.F., CP 04510, Mexico)
***************