Reproductive biology of albacore Thunnus alalunga.

Reproductive variables in albacore Thunnus alalunga were evaluated by gonad histology in samples of 132 males (58-118 cm fork length, L(F)) and 112 females (59-101 cm L(F)) that were collected from the western North Pacific Ocean from 2001 to 2006. In the sex ratio examination, males greatly outnumbered females in large adult fish (L(F) > 100 cm). Thunnus alalunga exhibited a protracted spawning period from March to September in the waters off eastern Taiwan and the Philippines, and the peak spawning activity occurred in March and April. Minimum sizes associated with the classification of mature fish were 78 and 83 cm L(F) for males and females, respectively. In addition, the largest L(F) of immature fish were 93 cm for males and 94 cm for females. The spawning frequency estimate in April was 1.7 days. Batch-fecundity estimates of 21 females (89-99 cm L(F)) ranged between 0.17 and 1.66 million eggs (mean +/-s.d. = 0.94 +/- 0.43). The relative fecundity estimates of the 21 females ranged between 9.2 and 92.4 oocytes g(-1) body mass (mean +/-s.d. = 50.5 +/- 22.8). The results presented in this study provide increased information regarding this species' reproductive-related characteristics than are currently available in stock status determinations.