brook trout were continuously exposed to depressed ph values from 4.0 to 6.0, at 0.5 unit intervals during a nine-month partial-chronic bloassay. at all ph levels above 4.0, juvenile fish exhibited greater than 96 per cent survival. although a ph of 4.0 was not acutely lethal, juvenile survival was poor. all trout exposed below ph 5.0 showed disturbances in acid-base balance and plasma electrolyte composition. juveniles did not grow or sexually mature at ph 4.0 and exhibited slower growth at ph 4.5, compared to fish exposed at higher ph's. inhibition of growth at ph 4.0 was attributed to starvation rather than h-ion concentration. spawning occurred at all ph levels except 4.0. eggs produced by females held at ph 4.5 were abnormal in shape and size, compared to those spawned by females held at or above ph 5.0. the total number of eggs produced at ph 4.5, however, did not differ significantly from the higher ph levels. embryos from parents exposed to ph 4.5 showed low viability and did not hatch. viability and hatchablllty of eggs held in the ph range, 5.0 to 6.0, was significantly reduced (p < .01) when compared to eggs held at ph 7.0. poor alevln survival occurred at all ph levels below 7.0. data on alevln growth at low ph was highly variable and hence inconclusive. results of the present investigation coincide with those of other studies on fathead minnow, brook trout and flagflsh, which indicate that reproductive success of these species is affected below ph 6.5.