Effect of Temperature Extremes on the Mortality and Development Rates of Coho Salmon Embryos and Alevins

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Abstract
The effect of water temperature extremes on embryo and alevin development rates and upper and lower lethal temperature limits for hatching have been defined for two coho salmon (Oncorhynchus kisutch) stocks. When held at constant incubation temperatures, embryos withstood temperatures between 1.3 and 12.4°C. Nearly 100% mortality occurred at 14°C in the upper range and below 1.3°C in the lower range. Most mortality occurred in the early embryonic stages, usually before the blastopore closed. Abrupt temporary changes in incubation temperature lasting 8 h and ranging from + 8.4 to - 6.2°C (including a drop to 0.1°C), resulted in little or no increase in embryo mortality except at the highest (10.2°C) incubation temperature. Temperature effects on development time were not linear, and small changes in temperature resulted in large changes in development rates, particularly at upper and lower extremes of temperature. A set of equations describes the relationship between temperature and centigrade uni...