Annual Reproductive Cycle and Spawning Frequency of the Female Yellowbelly Threadfin Bream Nemipterus bathybius in Kagoshima Bay, Southern Japan

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The annual reproductive cycle and spawning frequency of yellowbelly threadfin bream <I>Nemipterus bathybius</I> in Kagoshima Bay, southern Japan, were examined with histological sections of 612 ovaries. Based on the appearance of the most advanced oocytes, postovulatory follicles and atretic oocytes, ovaries were divided into the following seven maturity phases: immature, developing I and II, mature, spawning, spent, and resting. The appearance of the spawning phase revealed that the spawning season was June to October, with a peak-spawning season in July to September. The appearance of the most advanced oocyte by sampling hours showed that hydration occurs in the morning, and ovulation and spawning may arise from the evening to the night. The presence of multiple oocyte maturation stages, together with postovulatory follicles, evidences the species as a multiple spawner. In the peak spawning season, spawning frequency was estimated as 35% i.e. females spawned every 2.9 days.
日本水産増殖学会の論文