Effect of Egg Size on the Characteristics of Embryos and Alevins od Chum Salmon

抄録

Relationships between the size of fertilized eggs and characteristics such as weight, length and stages of development of hatched embryos and emerged alevins in chum salmon were studied. Eggs weighing from 150 to 400mg taken from chum salmon returning to the Tsugaruishi River in Iwate Prefecture were incubated at 11.0±0.5°C. The entire body weight, tissue weight, yolk weight, length, and developmental stages were compared among different size groups of the eggs at the hatching times and emergence. Irrespective of their differences in size at fertilization, eggs required almost the same duration for hatching and emergence. As was expected larger embryos gave larger alevins emerging at a less developed stage and with a greater condition factor whlie the smaller embryos gave smaller alevins emerging at a more advanced stage and with a lesser condition factor. Thus the larger alevins originating from larger eggs seem to have advantages in their early life history becauseof their energy rich condition. Disadvantages of the smaller alevins might be compensated by the relatively high fecundity and by their higher swimming activity at their emergence by more advance development.