著者

多部田 修 塚原 博

出版者

九州大学

雑誌

九州大學農學部學藝雜誌 (ISSN:03686264)

巻号頁・発行日

vol.21, no.2, pp.215-225, 1964-12

被引用文献数

2

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The anadromous Ugui-minnows, Tribolodon hakonensis hakonensis (Günther), one of the cyprinid fishes attained about 59 cm in total length, are distributed in the brackish waters and the estuaries along the shore from the Hakata Bay to the Karatsu Bay in the northern Kyushu, and they migrate mainly into Matsuura River to spawn. The authors have ovserved their spawning habits with reference to fishery in the spawning area of Matsuura River. The results obtained are as follows: (1) The spawning season of these fishes extends from February to April at 9-17℃ in water temperature. They ascend to the middle reaches of this river in January to March, ranging 16-25 km from the river mouth, where the artificial spawning beds are prepared for fishing by the fishermen. (2) Prior to spawning season the fishermen build the artificial spawning beds to attract the fish and to capture by the cast net (Plate 16, D, E, F, Fig. 5). It is a mound piled by gravel in the middle reaches to a cone-like form, 1.0-1.5 m in diameter and 0.5-0.7 m in height, with the several stones for control the water current in upper side and for the cast net in lower side (Plate 16, D, Fig. 5, Table 1). (3) The possible effects of some environmental factors upon the spawning of these fishes in this river are of close concern to rise in water level and turbidity (Fig. 3). Consequently the spawnings are usually carried out shortly after the rainfall, and are observed in several times during this season. In earlier spawning season the larger fishes are dominant, and the smaller ones become to abound gradually with the process of the spawning season. The male fishes are exceeding the female throughout the season, especially in the earlier (Fig. 4). (4) Before the spawning, the fishes are splashing at the surface of the deeps near the artificial spawning bed at intervals of 2 or 3 minutes, and it continues for about 30 minutes. Then two or more males followed one female pass harriedly over the bed, and the bed is often hidden by the many passing groups. In a little while, one female attended by three to seven males swims towards the bed. Arriving at the bed, they immediately thrust their head among the gravels and sometimes they spawn in that posture with slow quivering. Soon the female and males raise up their bodies and creep over the bed, and release the eggs and sperms among the gravels, pressing against the vent of female with the males and quivering all over. After this spawning act, females immediately leave from the bed as a rule, but most of males remain and join in the other spawning groups. It is observed that the spawning acts are not limited to two or three groups; as many as five groups at one time, and these spawning above mentioned last for about 30 minutes. (5) The spawning area of Matsuura River is divided into 19 fishing-grounds, which are granted to the fishermen by means of a bid (Imari area) or payment of a fixed price (Ochi area) (Fig. 7, Table 2). In all grounds the beds counted some 20 sets and the total catch in the be seems to have amounted approximately 750 kg in 1959.北九州の博多湾から唐津湾にいたる沿岸の湾奥部や河口水域には海産ウグイが生息し,初春の頃に産卵のため主として松浦川の中流部へ遡上する.ここでは産卵習性を利用した人工産卵床による瀬つけ場漁業が行われている.人工産卵床は中流部の瀬に作られ,特に水深10~70cm,流速30~70cm/secのところが選ばれる.松浦川における産卵期は2~4月(水温11~17℃)で,産卵盛期は年によつてその時期の降雨量に左右されて遅速がみられる.産卵は水温が10℃以上になり,降雨後に増水して濁度が高まると集中的に行われ,下流の産卵床に始まつて順次上流へ移り,主として1番,2番,3番イダの3つの主群があつて,産卵盛期もほぼ3回が認められる.産卵ウグイの体長は産卵初期に大きく,逐次小さくなり,性比については一般に雌に比して雄が極めて多く,初期には約7.5倍で,産卵期の経過とともに雌の割合が増加はするが,末期でも雄が多い.産卵に先だつてほぼ30分前から,産卵床付近の淀みで産卵魚の"とび"の行動がみられ,ついで雌1尾を2~3尾の雄が追尾する多数の群が床の上をつつきり,この行動は5分間ぐらい行われる.この産卵前の行動に続いて,雌1尾を雄3~7尾が追尾して産卵床に現われ,雌雄ともに礫中に頭をつつこんでただちに放卵放精するものもあるが,その多くは次第に腹部を床に接して雌雄が体を押し合いながら放卵放精を行い,この行動は5~10秒間である.産卵後の雌は一般に床を去るが,雄の多くはそのまま床に残つて他の産卵中の群に加わり,このような産卵行動は約30分間継続するのが観察された.人工産卵床は径5cmぐらいの丸石を用いて,直径1.0~1.5m,高さ0.5~0.7mの円錐状に築き,その上流側には水流を調節するために数個の石がおかれ,やや下流には投網を打つための台石がおかれる.この産卵床は産卵時の産卵行動と水流とによつて下流側へくずれ,ほぼ楕円形になる場合が多い.ウグイは一般に産卵後の床には再び産卵しない傾向があるため,産卵後は新しい石を追加する.松浦川の人工産卵床の漁場区域には2つの漁業協同組合があり,上流側の組合では16の漁場にわけ,それらは毎年入札によつて利用者が決められているが,下流側の組合では3つの漁場が一定価格で利用されている.これらの漁場のうちで,長い瀬をもつものでは2つの人工産卵床が作られるが,その多くは1つの床が築かれる.漁獲には主として投網が用いられ,人工産卵床における1959年の年間の漁獲尾数は約2,000尾,750kg,遊漁者の釣による漁獲尾数が約1,000尾,380kgで,松浦川の年間漁獲量は約1.1ton程度と推定される.