Abstract
The spawning season of Japanese Spanish mackerel Scomberomorus niphonius lasts from the middle of May to the beginning of July in the Seto Inland Sea.
The mean interval of individual spawnings ranged to 1.11-1.36 days, estimated by the ratio of females with hydrated oocyte. The relationship between batch fecundity (f) and body weight (w; g) was expressed as f =56.7w-5.71×104.
The number of large vitellogenic oocytes mainly corresponded to tertiary yolk globule stage, compared with that of hydrated oocytes in the same ovary, led to an estimate that they were spawn-ed during approximately between four and eight consecutive days. The next large vitellogenic oocyte group seemed to be formed during the pause period of about one day.
