| Budget Amount *help |
¥2,300,000 (Direct Cost: ¥2,300,000)
Fiscal Year 1997: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1996: ¥1,700,000 (Direct Cost: ¥1,700,000)
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| Research Abstract |
1.The reproductive behavior of Hexagrammos otakii, H.octogrammus and H.agrammus was observed using an underwater video camera system and SCUBA diving. The following results were chiefly obtained.
(1) The reproductive behavior of the 3 species was generally similar, so interspecific crossbreeding, in which female H.octogrammus responded to the courtship of male H.otakii. There is a possibility that concrete blocks of a quay loosen the native reproductive isolation.
(2) Sneaking followed pair spawning is 11 of the 26 spawnings. Paternity discrimination for 2 egg masses using microsatellite DNA suggested that 84% of all the eggs deposited in the nest were kin to the territorial male, and the remaining 16% were sired by sneakers.
2.It was examined which factor influenced to survivorship of the early life stages of a parental care fish, Hypoptychus dybowskii. Earlier spawned eggs underwent higher mortality during embryonic stages. The cause was predation by fishes such as hexagramids based on the observation with SCUBA diving. Analyzes on otolith daily increments suggested that earlier spawned individuals also underwent higher mortality during larval stages. However, earlier spawned individuals could gain larger body size upto adult stage. Survivorship during embryonic stages to spawning state required for seaweed forests.
3.The reproductive cycles of hair crab and helmet crab were examined by using the histological observation. These 2 crabs have the similar reproductive cycle, in which consist of oocyte growth, spawning, incubating, molting, and copulating. One cycle of hair crab take at least 2 or 3 years, but that of helmet crab does one year. Females stay under sandy bottom during long incubation period because of defenseless. Exhaustive protest of incubating females is important to reserve the crab resource.
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