Life history of a Gobioid fish, Sicydium japonicum TANAKA

Sicydium japonicum Tanaka is a fresh water goby, distributed in the South-Easten Japan, the Riu-Kiu Islands and the Northern Formosa (Fig.1). The authors studied its habits in the rivers of Miyazaki Prefecture, Kyushu. It lives under the stone of the mid-stream, feeding on Diatoms and Cyanophata growing on the stone-surface of the river-bed (Fig.2). The spawing-season seems to extend from early July to early September in the studied district. The number of ovarian eggs of a fish, 105 mm in total length, was 224,960. The breeding-rooms were found under the stones of the bed in the torrential mid-stream. The spawned eggs were attached to the under surface of the stone in masses. The spawned eggs were attached to the under surface of the stone in masses. The male parent fish was observed to stay in the room until the eggs hached (Fig.3). The egg is spherical, very small, 0.45 mm in diameter, with a bundle of adhesive filaments (Fig.4, A-D). The incubation-period seemed somewhat shorter than 2 days at the temperature about 25℃. The newly hatched larva is 1.5mm in total length with the particular body-form differing from the larvae of many other gobies in that it rather resembles to the newly hatched larvae from small pelagic eggs. It has not yet developed the pectoral fin, air-bladder nor melanophore on the eye-ball, with the mouth and anus not yet formed (Fig.4, E). The larva absorbed the yolk in 4 days after hatched, and attained 1.9 mm in total length. By this stage, the air-bladder, pectoral fin and attained 1.9 mm in total length. By this stage, the air-bladder, pectoral fin and melanophores on the eye-ball had appeared, the mouth and anus were formed (Fig.4, F).The hatched larva seems to descend into the sea with the flowing water, and spend its first winter in the coastal water of the sea (Fig.4,I). It grows to about 32mm in total length in the next spring, and approaches the river-mouth, feeding on plenctonic copepods (Fig.2, E: Fig.4, G). The juveniles, about 33 mm in total length, were found ascending the river in aggregation. They enter into the independent life in the mid-stream (Fig.4, H). It grows to 70 mm in total length in about 2 years and becomes mature.ボウズハゼは田中茂穂博士（1909）が高知県から得た標本によつてSicydium japonicumという種名で新種，新称として報告した淡水産のハゼの1種であるが，その後本州の中部以南及び屋久島，奄美大島、琉球列島，台湾北部等からも参集されている．本州東岸ではキタは茨城県箒川まで分布し，黒潮流域に面した房総半島，神奈川県，紀伊半島南部，高知県，宮崎県等の諸河川に産することが報告されている．九州西岸では鹿児島県川辺町及び川内氏で採集されているが，其れより着た，日本海沿岸地方からは採集記録がない．筆者等はここ数年間宮崎県下の諸川でこの特異な形態と生態を示すハゼの生活史を調べ，その太陽を知る事が出来たのでここに報告する．はじめに本研究に当り懇切な指導と原稿の校閲とを賜つた内田恵太郎教授に深謝の意を評すると共に，材料採集に当つて一方ならぬ御世話に与り且つ有益な御助言をいただいた水産庁南海区水産研究所矢部博技官，横田滝雄技官; 宮崎県淡水漁業指導所日高武達所長はじめ所員の方々; 鹿児島大学水産学部今井貞彦教授並びに貴重な文献の閲覧を許された松原喜代松博士，阿部宗明博士の諸氏に心からお礼申し上げる