Lead toxicity at different life stages of the giant prawn (Macrobrachium rosenbergii,de Man): considerations of osmoregulatory capacity and histological changes in adult gills

This study evaluated the acute toxicity of lead in different life stages of the freshwater prawn Macrobrachium rosenbergii, determined the effect of sublethal Pb concentrations on osmoregulatory capacity (OC), measured the Pb level in gills, and investigated the effect of Pb on the structure of the gills of adult prawns. The 24-, 48-, and 96-h LC₅₀ values for Pb to M. rosenbergii increased progressively with increasing life stage, from post-larvae (PL), juvenile to adult. The 24- and 48-h LC₅₀ values for post-larvae ranged from 0.01- to 0.09-mg Pb/L. The 24-, 48-, and 96-h LC₅₀ values for Pb were lower at 12 ppt than those at 0 ppt for either the juveniles or the adults. At 12 ppt, the 96-h LC₅₀ values in PL11, juvenile and adult were 0.47-, 0.58-, and 2.03-mg Pb/L, respectively. Meanwhile, at 12 ppt, the 96-h LC₅₀ values in PL11, juvenile and adult were 0.63-, 4.44-, and 7.98-mg Pb/L, respectively. In adults, the OC values of controls and prawns exposed to 2- and 4-mg Pb/L at 0 ppt were not significantly different. The OC of prawns exposed to and 2-mg Pb/L at 12 ppt increased by 72 and 109% from the OC of the control prawns. At media 12 ppt, the OC value of prawns exposed to 1-mg Pb/L was significantly different from that of prawns exposed to 2-mg Pb/L. The concentrations of Pb in gill tissues increased significantly in Pb exposed prawns both at 0 and 12 ppt. The level of Pb in gills of prawns exposed to 2-mg Pb/L at 12 ppt was not significantly different from those exposed at 0 ppt. The severe toxic actions of Pb were noted in gills of prawns exposed in media 12 ppt. Hyperplasia and necrosis were observed in gill lamellae, resulting in abnormal gill tips after Pb exposure at media 12 ppt. Since the effect of Pb is more pronounced in higher salinity (12 ppt) than in freshwater (0 ppt) it is clear that aquaculture of M. rosenbergii should be conducted in freshwater ponds.