Thermal Requirements for Maturation, Spawning, and Embryo Survival of the Brook Trout, <i>Salvelinus fontinalis</i>

Abstract

Thermal requirements for brook trout reproduction were determined at a natural day-length cycle and five constant temperatures (10–21 C) and one treatment that followed the seasonal temperature regime of Lake Superior. The optimum range for growth (unrestricted rations) and relative condition factor was 10–19 C. Survival was 90% or greater and gonad growth and secondary sexual characteristics were well developed at all temperatures. The maximum temperature at which males became functionally mature and contained motile spermatozoa was 19 C. Ovulation and spawning occurred at 16 C and lower. Water temperature had little influence on time of spawning, but had a major influence on spawning activity and egg viability. The upper median effective temperature (ET50) for the number of viable eggs spawned per female was 11.7 C. The upper median tolerance limit (TL50) for normal hatch was 12.7 C; the optimum temperature was near 6 C. Major factors influencing the number of embryos surviving to hatch were spawning and incubation temperatures and age of the embryo when exposed to test temperatures. Thermal criteria that recognize seasonal changes in their thermal requirements are recommended for self-sustaining brook trout populations.