Reproductive biology of the Japanese silver-biddy, Gerres equulus, in western Kyushu, Japan

The Japanese silver-biddy Gerresequulus (Temminck and Schlegel) is one of the most common shore fish in the costal waters of southern Japan and commercially important for the local fishery. In the present study, the reproductive biology of G.equulus is described for the first time and its spawning season and size at sexual maturity were determined. A total of 1081 specimens (484 males and 597 females) were collected in the Yatsushiro Sea, western Kyushu, Japan, from January 2001 to December 2002. Monthly changes in the gonadosomatic index exhibited higher values between June and September, with a peak in July, and the trend was similar for both sexes. Furthermore, the sequential development of the ovaries observed through the histological studies suggested that the spawning season of G.equulus continued from June to September. The female attained sexual maturity at a minimum size of 141 mm standard length. The simultaneous presence of postovulatory follicles and yolk globules in some ovaries indicated that this species is a multiple spawner.