1Graduate School of Bioscience, Tokai University, Shimizu, Shizuoka 424-8610, 2National Research Institute of Far Seas Fisheries, Fisheries Research Agency, Shimizu, Shizuoka 424-8633, Japan
The spawning frequency and batch fecundity of skipjack tuna Katsuwonus pelamis collected from the tropical west-central region of the Pacific Ocean between July 2003 and April 2006 were examined. The estimated mean spawning frequency of individuals collected between 06:00 and 15:00 was 0.50, indicating the spawning intervals of 1.99 days. Batch fecundity was estimated by counting the number of advanced oocytes with diameter≥0.5 mm at the final mature phase (i.e. those containing a migratory nucleus stage or hydrated oocyte in the ovary). Of 23 females analyzed, the mean batch fecundity and relative batch fecundity were 615,000 oocytes and 147.8 oocytes per gram of somatic weight, respectively.