| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1994: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1993: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1992: ¥1,100,000 (Direct Cost: ¥1,100,000)
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| Research Abstract |
In the present study, sexuality, growth, body size of two tilefishes species, Branchiostegus auratus and B.albus were examined. In both species, males were larger than females, suggesting sex change in these species. However, histological investigations revealed that males had no secondary testes and nor intermediate gonads which shows sexual transformation. It was concluded that sex change do not take place in these two species. Body size difference found between both sexes is due to differential growth of mortality between the sexes. Age determination in these species suggested that males grow faster than females in B.auratus and females dies earlier in B.alubus.
One of the important findings in the present study was spawning behavior of captivity reared B.japonicus. When a male and a female was kept in a tank, both fish hide themselves in a plastic pipe provided as shelters nearly all day. Near dawn, however, both fish came out of the pipes and the female approached the male. Soon after this, the pair rushed upward and spawned pelagic eggs. One of the characteristics of these eggs was that eggs were evneloped bymucus. The egg mass in the mucus envelop floated at the surface for about 30 minutes and the mucus disappeared. Eggs dispersed after mucus disappeared.
Fertilization rate of the eggs in the mucus envelop was examined and revealed it was as low as 0-20%. The reason for low fertilization rates were not known, but artificial fertilization of the eggs floating in the mucus with sperm from natural specimens resulted in fertilization rate as high as 70%. These results suggested that eggs were mature and fertilizable. It was supposed that males were not fully mature due to the stress in captivity or size ofthe tank was inadequate for the completion of spawning behavior. It was suggested that constant supply of fertilized eggs will be possible after developing the methods for effective spawning behavior and further study on the maturation of captivity reared males.
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