有明海産魚類生活史の研究

Triaenopogon barbatus Gunther is plump goby, some 70 mm in total length, with barbels and trilobed teeth bands (Fig. 2). It is distributed in China, Formosa and Japan, and abundantly found in Ariake Sound, on the western coast of Kyushu, Japan. Ariake Sound is a large bay of muddy, shallow water, less than twenty metres in depth at the inner part ; and there occur fast tidal currents. The fish-fauna of this sound, including more than twenty species of Gobioid fishes, shows special characteristics different from other bays of Japan (Fig. 1). The three allied Gobioid fishes, Triaenopogon barbatus (Giinther), Tridentiger trigonocephalus (Gill) and Tridentiger undicervicus Tomiyama live a similar bottom-life in the same muddy shallows in the innermost part of the sound. Triaenopogon barbatus (Gunther) inhabits the oyster-beds of soft muddy tidal flat (Fig. 3). The sexes are easily distinguished in this goby of over 40 mm in total length, by the structure of the urogenital papilla. In the male, this organ is conical and pointed at its tip, whereas in the female it is truncate at its tip. The ripe ovarian eggs included two egg-groups, one the ripe egg-group, 0.48-.-0.90 mm in egg-diameter, and the another the unripe egg-group, less 0.05 mm. This ripe egg-group seemed to be spawned at one time. The number of ripe ovarian eggs is enumerated 2,610 to 23,365 in four individuals (Table 1). The ripe testis is a white, thick band-form organ with a leaf of the appendant organ ("Seminal vesicle" : Weisel, G. F. 1949). The spawning occured in the above-mentioned habitat from May to September, mainly in July. The spawned eggs were deposited, in one-layer, on the inner surface of the cleaned empty shell of Ostrea rivularis Gould on the tidal flat. The number of eggs of one mass was enumerated 7,791 and 15,841 in two cases ; and each spawned egg-mass wholly consisted of the eggs in similar developmental stage as were observed in over twenty cases. The spawning-act seemed to occur at the tidal flood, and when the act finished the female parent fish left the nest, whereas the male which had remarkably compressed head, was found guarding the spawned eggs until they hatched (Fig. 3). The observational data collected from the spawning-ground seemed to show the polygamous habit of the large male fish. It is yet unknown how many times one female fish spawned in one season. In this species, the size of the nest generally corresponded with the size of the guarding male parent fish. Also the size-order of the nest (oyster shell) of the three, allied gobies, spawned in the similar spawning-ground of oyster-bed at the same time, were recognized as corresponding with the size-order of the male parent of these gobies ; that is Triaenopogon barbatus, Tridentiger trigonocephalus, and Tridentiger undicervicus (Table 2). The spawned egg is demersal, ellipsoid in shape, about 1.5 mm in longer axis, 0.5 mm in shorter axis, with a bundle of adhesive filaments at its basal end. The incubation-period is about four days at the water-temperature about 25℃ (Fig. 4). The newly hatched larva is about 2.5 mm in total length. This larva consumed its yolk entirely in three days after hatched at the same water-temperature in egg-development (Fig. 5). The post-larvae, less than 10 mm in total length, was not yet collected. The post-larvae of 10-17 mm were found to live a swimming-life in the deeper drainage course of the mud flat from June to October, feeding on planktonic Copepods and Crustacean larvae. Together with the larvae of this goby, two gobies, Tridentiger trigonocephalus and T. undicervicus of similar size, 10-15 mm in total length, were collected with the set-nets in the estuary from June to July. The juveniles, over 17 mm in total length, were found from July to October entered into the bottom-life in the same habitat of the adult. The examination of gut-contents of the young as well as the adult fish showed that Annelida, small Crustaceans, squid, and young fish, including the young of this goby and Tridentiger trigonocephalus, constitute the diet. This goby seems to grow 40-85 mm in total length in a year, and to become mature in most individuals ; 85-115 mm in two years ; over 120 mm in three years, based upon the size-frequency. The smallest female adult examined was 53 mm in total length (43 mm in standard length). The life-span seemed to be over three years.