| Research Abstract |
1.Distribution and migration of Ayu.
Age, birthdate, and migration history were examined for larvae and juveniles collected from coastal waters around the mouth of Miya river, Mie prefecture, and for adult fish from Miya river and Nagara river, Gifu Prefecture, using otolith microstructure and microchemistry (Sr : Ca ratio). After drifting into the sea, the larvae shifted the distribution from the coastal areas to the surf zone before they grew to 20 mm long. They subsequently occurred in the estuary after they reached 30-40mm, and then began their upstream migration. The earlier born and larger size juveniles tended to go upstream earlier in the spring. Furthermore, fish that were born earlier and underwent the upstream migration earlier at a larger size showed a tendency to spawn earlier and larger size. We also examined carbon and nitrogen stable isotopic compositions of "Shio-ayu" which distributes in the lowest reach in Choshi river, Mie Prefecture, and determined that it distribut
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ed in estuary and feed on estuarine attached algae as a major food.
2.Migration of the Japanese eel.
Otolith oxygen isotopic composition of glass eels collected from Tanegashima Island, Japan, was examined for determining the spawning temperature and depth. The oxygen isotopic composition of the otolith core was not different from those of otolith neighboring region deposited during leptocephalus stage, suggesting that the spawning temperature and depth were 12-28℃ and 320-50 m in the water column, respectively. Otolith microstructure and microchemistry (Sr : Ca ratio) of glass eels recruited in Ise bay and Kushimoto, Wakayama Prefecture, suggested that the duration of coastal migration was 20-24 days. The duration between the arrival at coastal waters and recruitment was estimated to 9-12 days. There was no difference in those durations among glass eels from the two sampling sites. The glass eels were suggested to migrate directly to each. river they recruited after they detrained from the Kuroshio.
3.Migration and metamorphosis of Conger eel.
Otolith microstructure and microchemistry (Sr : Ca ratio) of conger eel larvae collected from Ise bay and Hamashima, Mie Prefecture, and Oarai, Ibaraki Prefecture, were examined. There was no difference in ages at recruitment and at beginning of metamorphosis among the larvae collected from three sampling sites. They were found to undergo one month coastal migration with beginning of metamorphosis, after 3 month oceanic migration. Organ differentiation was completed for 60-80 days after the beginning of metamorphosis with the functional establishment of stomach. Less
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