Effects of lead loads on branchial osmoregulatory mechanisms in the rainbow trout Oncorhynchus mykiss.

Exposure of rainbow trout to lead chloride (PbCl2, 1 ppm) in fresh water killed all animals within 16 days. Exposure to this lethal dose for 6 days only showed a significant increase in the haematocrit. Calcium, sodium and chloride concentrations in plasma were not notably modified. Both the influx and the net flux of sodium fluctuated much less than the diffusional water fluxes through secondary lamellae in gills. Branchial Na,K-ATPase, Ca-ATPase and HCO3-ATPase activities were not sensitive to lead toxicity. Lead caused a cellular 'wave-shaped' degeneration and renewal with modification in the number and morphology of chloride cells. Results are discussed in relation to the hydromineral balance of the trout.