| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1990: ¥400,000 (Direct Cost: ¥400,000)
Fiscal Year 1989: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1988: ¥1,400,000 (Direct Cost: ¥1,400,000)
|
|---|
| Research Abstract |
Fish generally swim against the current to maintain their position in a river ; they always turn their heads toward the upper part of the river. However, in the case of salmon smolts, they have to swim to the sea early in life. If they maintain their general behavior vis-a-vis the water current, they cannot reach the river mouth. Thus, we can expect that some changes will occur in their swimming behavior. In order to observe these changes, we made a circular experimental tank which had a current. If the young salmon were cultivated in water with a current continually after hatching, they alwaysmaintained their position in the stream by swimming against the current. We did not observe that they swam with the current in the experimental tank throughout the observation time (until 130 days after hatching). On the other hand, if the young salmon were kept in still water for some period of time and then moved to the experimental tank, they soon started to swim with, and faster than, the cur
… More
rent. This catadromous migration continued for several days. After this, they reversed the swimming direction from downstream to upstream and kept their position in the stream. Staying in still water for some period of time may trigger the downstream migration. The swimming speed during catadromous migration was 17 cm/sec. This speed was faster than the water current (5-7 cm/sec). The distance traveled during this period, which was calculated from the swimming speed and time, seems to be enough to reach the river mouth.
In the long cultivation of salmon fingerings in fresh water, they grew to a length of 30 cm about 22 months after hatching, and gonad growth was observed in both females and males. We were unable to succeed in the cultivation of the salmon for longer than two years because they lost their appetites and weakened.
The qualitative and quantitative analysis of amine substances in the brain and skin of salmon fingerings is now being carried out in order to determine the transition mechanism of their swimming behavior against the water current. Less
|
