Preliminary experiment of effects of high water temperature on maturation of adult chum salmon

To evaluate the effects of high water temperature on the final maturation of chum salmon (Oncorhynchus keta), 3 females and 3 males were kept in tanks at different temperatures (normal, 11 degree C; high, 20 degree C or 22 degree C), and cross-fertilization was conducted using the surviving mature fish. Females held at 20 degree C ovulated on the third day of holding, while all females held at 22 degree C dried by the fifth day without ovulating. In the ovary of one of the dead females, morphological changes such as over-maturation (aggregations of yolk globule) were recognized. Eyed egg ratio and hatched fry ratio of eggs fertilized with males held at 20 degree C were lower than that of eggs fertilized with males held at 11 degree C. Also, survivals of eggs fertilized with females held at 20 degree C were lower until eyed-egg and the subsequent stages, indicating an influence upon egg quality that cannot be evaluated from the external appearance. These results suggest that water temperature higher than 20 degree C may affect the mortality of adult chum salmon, final maturation, and ovulation.