The Bionomics and Life History of the Eleotrid Fish, Eleotris oxcephala TEMMINCK et SCHLEGEL

Eleotris oxcephala TEMMINCK et SCHLEGEL is a Eleotrid goby. It is distributed in the south-eastern Asia. The full grown fish attains to over 270mm in total lenth and 230 g. in body-weight. In the southern Japan it lives a bottom life in pools situated in the lower part of river. It is nocturnal fish and feeds on small fishes, shrimps and crabs. The sexes easily distingushed by the from of urogenital papilla and the second dorsal fin (Plate XVIII, Fig. 1, 2). The number of ripe ovarian eggs was enumerated as 56,206 and 15,000 in two small size specimens, 172mm and 94mm in total length respectively. The spawning period seemed to extend from July to August in Kyushu. The spawning occurred in a shallow pool, the ordinary habitat of the adult (Plate XVI, 3, 4). A egg-mass was collected from an old vacant bamboo lying on sandy mud bottom of the pool. The eggs were deposited in one layer mass to the inner wall of the bamboo-nest. The parent, female 152mm in total length and male 157mm, stayed in the nest when the just spawned eggs were found. The fertilized egg is demersal and adhesive one with adhesive filaments at basal end. It is an electric bulb shaped, 0.37～0.43mm in long axis and 0.31～0.34mm in short axis. This is one of the smallest teleostean eggs. The incubution-period of the egg is about ten hours at temperature 25～28℃. This is the shortest one of the incubation-period of teleostean eggs published (Fig. 1, A, B, C, D). The newly hatched larva is tiny one, 0.94～1.11mm in total length, with the less developed body-features than thats of Gobiid larvae described generally (Fig. 1, E). This larva is similar in form to the Gobiid larva hatched out from the small eggs, smaller than 0.4mm in egg-diameter, as thats of Ctenogobius stigmatus (Kuntz 1916), Mir ogobius lacustris (Blanco 1947), Sicyopterus extraneus (Mancop 1953) and Sicyopterus japonicus (Dôtu and Mito 1955). The larva metamorphosed remarkably in yolk-sack stage, and attained to l.87～2.04mm in total elngth in about 85 hours after hatching (Fig. 1, F, G H). The juvenile, 13.0mm in total length, was collected in August from a estuary in the Koshiki Islands, Kagoshima Pref., Kyushu. It entered already into a bottom life (Fig. 1, I). The form of this juvenile is similar to that of the juvenile of Eleotris melanosoma described (Blanco 1958). The young, 24～82mm in total length, were collected in December from the estuary of the River Ooyodo, Miyazaki City, Kyushu. The young concealed themselves in a bundle of leaves set there for eel-capture