Effects of transferring pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon embryos at different developmental stages to a low incubation temperature

Abstract

We transferred embryos of pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon from 8 to 2 °C at five stages of development: 16-cell stage, blastula stage, completion of epiboly, early eye pigmentation, and late eye pigmentation. Survival rates of the embryos increased the later in development that they were transferred to 2 °C. All pink salmon blastulas transferred died, whereas 50% of chum salmon blastulas transferred survived until hatching. After epiboly was complete, survival rates of the embryos subsequently transferred to 2 °C were usually in excess of 75%. Chum salmon embryos had higher survival rates than did pink salmon embryos at all transfer stages. Significant differences were found in embryo survival rates among stocks within species and among families within stocks. Fry from early-spawning chum salmon took longer for exogenous yolk absorption ("button-up") than did those from late-spawning ones. Alevins and fry from early transfers were generally smaller than those from later ones. Different trends in embryo and alevin survival rates and alevin and fry size among stocks within species and among families within stocks were assumed to be indicative of adaptive variation to variable natural incubation environments.