The development of chinook (Oncorhynchus tshawytscha) and chum salmon (Onchorhynchus keta) embryos and alevins under varying temperature regimes

Chinook (Oncorhynchus tshawytscha) and chum salmon (O. keta) embryos were initially incubated at 4, 8, or 12 °C and then maintained at the same temperature or systematically transferred at completion of epiboly (early transfer) or complete eye pigmentation (late transfer) to each of the other incubation temperatures. For both species initial incubation at 8 or 12 °C resulted in higher embryo and alevin survival rates than initial incubation at 4 °C. Increasing or decreasing temperature regimes had little effect on embryo and alevin survival rates. Transfers after epiboly or completion of eye pigmentation had little influence on subsequent survival rates, except the early and late transfers of chinook salmon embryos from 4 to 12 °C, which resulted in an increase in alevin mortality. Hatching and emergence times varied inversely with temperature, and chum salmon generally hatched and emerged sooner than chinook salmon. Decreasing temperature regimes produced longer and heavier chinook salmon alevins and fry, but constant incubation at 8 °C or early or later transfers to 8 °C resulted in longer and heavier chum salmon alevins and fry. Temperature regimes that simulate those experienced by a species during natural incubation tend to enhance survival and alevin and fry size. Different trends in embryo and alevin developmental characters between species and among families within a species were assumed to reflect adaptations to variable natural incubation conditions.