White sucker (Catostomus commersoni) eggs were incubated in water of high (250 μmhos/cm) and low (20 μmhos/cm) conductivity with nominal pH ranging from 4.2 to 8.0. At pH 4.5 and below in water of low conductivity no eggs survived to hatching. In high conductivity water at pH 4.5 a few prolarvae hatched but were deformed and soon died. At pH 5.0 and above the total hatch was the same at either conductivity level. However, at pH 5.0 there were body deformities and abnormalities in the vascular system and none of the prolarvae survived to the swim-up stage. At both conductivity levels there was a reduction in swim-up at pH 5.3 compared with the control, but none at pH 5.8. Low pH had a delaying influence on the absorption of the yolk sac.