No abstract

Litopenaeus schmitti juveniles (total length 15 AE 0.4 cm) were exposed to different concentrations of nitrite using the static renewal method at different salinity levels (5&, 20& and 35&) at pH 8.0 and 20°C. The 24, 48, 72 and 96 h LC50 values of nitrite in L. schmitti juveniles were and 38.88 mg L À1 at 35& salinity. As the salinity decreased from 35& to 5&, susceptibility to nitrite increased by 33.4%, 46.7%, 69.2% and 103.3%, after 24, 48, 72 and 96 h of exposure respectively. Furthermore, we found that exposure of shrimp to nitrite caused an increase in oxygen consumption by 137.3%, 99.2% and 81.4% and an increase in the ammonia excretion level by 112.5%, 87% and 64.3% with respect to the control with decreasing salinity levels.

Penaeid shrimps are important resources for worldwide fisheries and aquaculture. In Brazil, Litopenaeus schmitti is an important commercially exploited species, and the ideal animal for studying the impairment caused by the effects of heavy metals often detected in coastal areas. The main purpose of the present study was to detect the acute toxicity of lead (Pb) in L. schmitti and to investigate its effect on oxygen consumption and ammonia excretion for different salinities. This has not been studied in this species before. Lead was significantly more toxic at salinity 8 than at 20 and 33. The oxygen consumption and ammonia excretion were estimated through experiments performed on each of the fifteen possible combinations of three salinities (33, 20 and 8), at the temperature of 21 °C. Cadmium showed a significant improvement in oxygen consumption at salinity 8, and results show that the oxygen consumption increases with respect to the lead concentration. At the highest lead concentration employed (2.12 10-2 mg/L), the salinity 8 and the temperature at 21 °C, oxygen consumption increases 131% in relation to the control. In addition, after separate exposure to lead, elevation in ammonia excretion was obtained, which was 88.2% higher than the control. The results show that lead is more toxic to L. schmitti at lower salinities.