Spawning time and frequency of bigeye tuna, Thunnus obesus
1991
Nikaido, H. (Japan Sea Farming Association, Ishigaki, Okinawa. Yaeyama Station) | Miyabe, N. | Ueyanagi, S.
This study investigated spawning time, spawning frequency and the number of eggs spawned per day for bigeye tuna. Gonads were collected from bigeye tuna caught by two longline boats operated in the waters off Java and in the waters of south-western offshore of Hawaii. Gonosomatic index and frequency distributions of egg diameter from the maturing ovaries were analyzed. Gonads were also histologically examined to investigate the maturation of gonad and the degeneration process of postovulatory follicles. The results clearly indicate the bigeye tuna is a multiple spawner and mature female spawns almost every day. Spawning seems to take place from at around 19:00 to midnight in both areas. The relationship between fork length and the number of eggs spawned per day was also estimated based on the egg counts of the most advanced egg group in the maturing ovaries
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