Chum salmon (Oncorhynchus keta) larvae were incubated in gravel-filled cages placed in two experimental Japanese-style keeper channels having 40 and 80 L/min total flow, at three successive locations having 0, 46 000, and 92 000 eggs (or alevins) upstream. Minimum dissolved oxygen was 6.21 mg/L, maximum un-ionized ammonia was 0.18 μg/L, pH varied from 7.18 to 6.83, and temperature ranged from 7.8 to 8.2 °C. Preemergent fry showed small but significant decreases in mean fork length, with increasing distance along both channels 50 d after hatching. Weights decreased similarly but nonsignificantly in both channels. Stage of development (expressed as KD-index) was constant in all locations except the bottom location of the low-flow channel, which showed a significant delay. Survival was uniformly high with no differential mortality among locations or flow rates. We conclude that deteriorating water quality measurably reduced larval development rate, growth rate, and yolk-conversion efficiency. Main effective factor was dissolved oxygen. Standard channel loading and flow criteria are adequate for short incubation channels only.