マイワシの生長過程に関する研究-III

與謝内海,久美浜湾におけるマイワシ脊椎骨数の変動

抄録

The fries of sardine are released artificially into the inlets, Yosanaikai and Kumihama Bay, in June or July every year. As there are naturally entered fry, they mingle each other and stay there growing for a while.
Accordingly, fished sardines in summer are considered to be composed of both naturally entered school and artificially released one.
Numbers of vertebrae were counted to estimate the process of mixture of both schools through the fishing period.
Results obtained are as follows.
1) The average vertebral number of Yosanaikai sardine is higher in the first period of fishing, and then successively it becomes lower till the middle period of fishing, owing to the increase of additional rate of released fish to the caught group.
2) In the Yosanaikai, the released fish were caught as a rate of 15% on total catch during the fishing season in 1954. The increasing rate of catch was more remarkable in Kumihama Bay, where naturally entered fries seem to be scarce.
3) Average vertebral number of sardine fries in Yosa naikai were found higher than that in thelast period of fishing. This indicates that the sardines reared in environments of low water temperature during the larval stage are able to stay in inlet waters of lower salinity for a long period.