Spawning time, spawning frequency and fecundity of Japanese chub mackerel, Scomber japonicus in the waters around the Izu Islands, Japan

Abstract

Female Japanese chub mackerel, Scomber japonicus, were collected in 1993 from April to June (36 days), in the water around Izu Islands, Japan, which is one of the primary spawning areas. Spawning time, spawning frequency and batch fecundity were determined by histological methods. Temporal frequency of hydrated oocytes and new postovulatory follicles showed that female chub mackerel spawned actively from 22.00 to 24.00 hours. The average spawning frequency was 17.4% during this sampling period. We estimated that chub mackerel spawned every 5.7 days (6.3 times) during these 36 days. Fifteen females spawned almost every day. Twelve females which had hydrated oocytes in their ovaries were used for estimating batch fecundity. The average batch fecundity was 89 200 oocytes per female, and the relative batch fecundity was 158 eggs per gram female wet weight. The batch fecundity was significantly correlated with condition factor. This shows that batch fecundity was affected by nutritional state of spawning female.