While in grad school one of my jobs was to release the day's collection of chum fry, They were held all day in big circular tub (multi-thousands) and the drained out a 4" pipe. After dark. Shined a flashlight on the outfall once and there was a cutthroat, whose head just fit, filter-feeding on the stream of fry as they came out. We also tossed the cutts coho smolts which they gobbled down.