台灣近海扁紅?生殖生態之研究

Abstract

During 1971, 752 (♂403, ♀349) Decapterus kurroides aka-adsi ABE caught from the waters off Nanfangao and Kaohsiung by hand liners were collected at monthly interval. Maturity of the fish were examined and the fecundity of the females were estimated. Their seasonal fluctuation and geographical variation were compared. The results revealed as follow: 1. Judging from the polymodel distribution and their monthly fluctuation of ova diameter, the type of development of eggs of Decapterus kurroides aka-adsi ABE is considered to be Asynchronism. Eggs may be deposited fractionly throughout the spawning period. 2. The reproductive activity begins in January and ends in September. The early spawning may take place in May. During this period, maturing fish may aggregate sexually and agely to form several shoals for spawning migration. 3. Sex ratio of the species is nearly 1 to 1, but it variates significantly during the sexually active months. 4. In the most fecund month, the total fecundity of the fish examined is about 457,311+66,892, and the relative fecundity is 1,552±154/per gram of fish. 5. the estimated number of eggs per spawning of the examined fish is from 110,727 to 140,171. 6. The biological minimum size (or size at onset of sexual maturity) is estimated to be from 220 mm to 240 mm. 7. The optimal water temperature for spawning is considered to be from 24℃ to 26℃. 8. The main spawning shoals were the I+ and II+ age classes (250 mm-300 mm in fork length), While the larger fish of the O+ age class may also take part in spawning.