Toxicity of cadmium for silver catfish Rhamdia quelen (Heptapteridae) embryos and Larvae at different alkalinities

The present study evaluated the effect of waterborne Cd in eggs and larvae of silver catfish, Rhamdia quelen, at two alkalinity levels (63 and 92 mg . L-1 CaCO3): 0.5 (control), 4.5, 8, and 18 mu g . L-1 Cd. The fertilization rate was similar in all treatments, but the number of eggs with irregular surface was significantly higher in those exposed to 18 mu g . L-1 Cd and 63 mg . L-1 CaCO3. Three days after hatching survival of larvae exposed to 4.5 and 8 mu g . L-1 Cd and 63 mg . L-1 CaCO3 was significantly lower than that of control larvae, and 21 days after hatching survival decreased with the increase in waterborne Cd levels and total cadmium accumulation in the larvae. These significant differences and relationships were not observed in larvae maintained at 92 mg . L-1 CaCO3. Furthermore, in the lower alkalinity, a higher incidence of barbels and spinal column deformities was observed in the highest waterborne Cd concentration. At the end of the experimental period, 21 days after hatching, larval survival rate, length, weight, head height, membranous layer thickness, and biomass decreased with the increase in waterborne Cd levels in the lower alkalinity. However, these relationships were not observed in larvae maintained at 92 mg . L-1 CaCO3. The percentage specific growth rate was lower in larvae exposed to the highest waterborne Cd concentration at 63 mg . L-1 CaCO3. These results suggest that alkalinity of 92 mg . L-1 CaCO3 reduces waterborne Cd toxicity in silver catfish larvae.