Journal
FISHERIES SCIENCE
Volume 72, Issue 5, Pages 985-994Publisher
BLACKWELL PUBLISHING
DOI: 10.1111/j.1444-2906.2006.01247.x
Keywords
batch fecundity; oocyte stage; Pacific bluefin tuna; sex ratio; spawning frequency; spawning season; Thunnus orientalis
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Pacific bluefin is a highly valuable pelagic species that inhabits a broad range in the North Pacific Ocean. The reproductive biology, especially for the spawning aggregation in the south-western North Pacific Ocean, is not well understood. Thus, a total of 119 paired ovary specimens were collected from the Taiwanese longline fleet during the 1999 fishing season (late April through June) to gain a better understanding of important reproductivity-related stock parameters associated with this species. The following conclusions were made: (i) condition factor decreased from late May to early June; (ii) the sex ratio might be 1:1 for spawners; (iii) the gonadosomatic index stayed at a relatively high level and markedly increased from late May to early June; (iv) histological examination of oocytes indicated that all specimens were sexually mature; (v) spawning activity appeared to start in May and peak in late May to early June; (vi) batch fecundity increased with fork length; and (vii) preliminary estimates of spawning frequency between batches ranged 2-4.5 days based on analysis of postovulatory follicles.
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