EFFECT OF EGG SIZE ON THE CHARACTERISTICS OF EMBRYOS AND ALEVINS OF CHUM SALMON

Relationships between the size of fertilized eggs and characteristics such as weight, length and stages of development of hatched embryos an d emerged alevins in chum salmon were studied. Eggs weighing from 150 to 400 mg taken from chum salmon returning to the Tsugaruishi River in Iwate Prefecture were incubated at 11.0+/-0.5 degrees C. The entire b ody weight, tissue weight, yolk weight, length, and developmental stag es were compared among different size groups of the eggs at the hatchi ng times and emergence. Irrespective of their differences in size at f ertilization, 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 while t he smaller embryos gave smaller alevins emerging at a more advanced st age and with a lesser condition factor. Thus the larger alevins origin ating from larger eggs seem to have advantages in their early life his tory because of their energy rich condition. Disadvantages of the smal ler alevins might be compensated by the relatively high fecundity and by their higher swimming activity at their emergence by more advance d evelopment.