Modification of the Sexual Cycle in Brook Trout (Salvelinus Fontinalis) by Control of Light

Abstract

To facilitate handling of brook trout fingerlings during winter and to permit a shorter holding period for catchable‐sized trout, experiments on shortening the sexual cycle by control of light were conducted on a commercial scale from 1939 to 1950. Light was increased over normal daylight and then decreased below normal daylight. This procedure caused fish to spawn as early as late July. Artificially lengthening the day in the fall retarded spawning. Early spawned eggs had a higher survival than normally spawned eggs and general hatchery efficiency was improved when early eggs were used.