|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1995 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1994 : ¥700,000 (Direct Cost : ¥700,000)
Fiscal Year 1993 : ¥900,000 (Direct Cost : ¥900,000)
During 1993 to 1996 captive experiments of the Japanese common squid, Todarodes pacificus to clarify the reproductive biology, I get some new informations about the maturation process of captive female, the egg mass formation by spawning and the artificial fertilizatin and development through hatching in this species. The results are as follows.
1. Maturation of female : Copulation by male do not accelerate yolk formation of oocytes in oavry. The higher temperarture in captivity may promote the ovulation and the spawning.
2. Egg mass formation by spawning : The female can produce gelatinous egg masses, about 60 to 80cm in diameter, within 8 minutes. Egg masses were estimated ontained about 100,000 to 200,000 ova. The ova lay in an appearently uniform mass of gelatinuous substance that originated from the oviducal gland. This was covered by the surface layr of jelly for the nidamental gland.
3. Characteristics of egg mass : Egg masses were slightly buoyant and not broken until hatching. Ex
amination of the egg mass surface layr revealed that the outer nidamental gland gel was effectve in preventing crustaceans, protozoans, and bacteria from entiring the egg mass.
4. Effect of temperature on development and survival of paralarvae : We exploited a new artificial fertilization technique on ommastrephid squids. The embryonic development and survival of T.pacificus paralarvae were examined at several temperatures between 3ﾟC to 29ﾟC.Normal embryonic development occurred at temperatures between 14.0 to 26ﾟC,with highest embryonic survival rates occurring between 14.7 and 22.2ﾟC.
5. Survival and behavior of paralarvae : Paralarvae survived up to 13 days after hatching, with the highest survival rates occurring at 15ﾟC.Hatching paralarvae swim upward immediately, with many animals found concentrated along the surface layr. We saw no evidence of any feeding by the paralarvae within the egg mass after hatching, however the longer develoment time within the egg mass indicates greater opportunity for pre-hatching paralarvae absorbing organics from the mucus originated from the oviducal gland gel. Less