抄録
The present study examined the effects of extended daylength (18:00-24:00) on ovarian maturation and HCG-induced spawning in yellowtail fed moist pellets. In the experiments conducted in 1991, 1992, and 1993, the daylength was extended by 6 h for 20 or 28 days followed by an injection with hormone, HCG.
Female yellowtail brood stock kept under extended daylength were induced to mature more rapidly than those kept under natural lighting conditions. The mean number of eggs produced per fish was more than 200×104 in the extended daylength groups, compared to about 100×104 in the control groups. The rate of normal eggs, rate of hatching, rate of normal larvae, and survival activity index (SAI) of larvae obtained from the extended daylength groups were significantly higher (p<0.01) than those of the control fish. These results demonstrate that manipulation of daylength is an effective method for acceleration of final maturation in female brood stocks of yellowtail.
