ゴマハゼ

Gobius lidwilli McCulloch, the smallest vertebrate in Japan, is distributed along the coast of South-Western Japan. It is a plump, semi-transparent goby with rather a few melanophores on the body (Fig. 1). The fully mature females range 17～21 mm in total length, and the males 16～20 mm. There appears a disproportion in the number of the sexes : the female being more numerous in every lot collected (Table 1). The goby lives a gregarious and semi-pelagic life in the littoral zones of the inlets all year round, feeding on the planktonic copepods. The number of ripe, ovarian eggs was enumerated as 154～311 (Table 2). The spawning-season seemes to extend from June to August in Tomioka, Amakusa Islands, Kumamoto Pref., Kyushu. The fertilized egg by the artificial insemination is demersal, adhesive and ellipsoid in shape, 1.2 mm in long axis and 0.7 mm in short axis, with a bundle of adhesive filaments at the basal end of the rather thick egg membrane (Fig. 2). The Kupffers vesicle never appears throughout developmental stages. The incubation period was 4 days and 12 hours at the water-temperature 24～27℃. The spawning behaviour both in the natural habitat and in the aqarium is yet unknown. The newly hatched larva is 1.8 mm in total length, and swims freely in the glass-jar. The postlarvae, 6～9 mm in total length, were found from July to September at Tomioka, living a life as the adult (Fig. 3). The collected specimens show that the female grows to 17～20 mm in total length in a year, and the male to 16～19 mm, and become mature. The lifespan seems to be over 2 years.