著者

馬場 吉弘 長田 芳和

出版者

The Ichthyological Society of Japan

雑誌

魚類学雑誌 (ISSN:00215090)

巻号頁・発行日

vol.52, no.2, pp.125-132, 2005

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To clarify the early life history of pale chub, <I>Zacco platypus</I>, and the mechanism for avoiding egg predation, the spawning behaviour, egg and larval distribution in spawning redds, and emergence time of larvae from the redds were investigated in the Saho River, Osaka Prefecture, Japan. In pair spawning, the male applied lateral pressure to the female, and stirred up the river bed with its anal and caudal fins when eggs were released. The female occasionally rotated in the redd at the end of spawning behaviour. Some satellite males and sexunknown individuals occasionally dashed into the spawning redd. Single females averaged 1026.4 mature eggs, spawning 94.5 eggs during each of 10.9 spawning acts per day. The number of eggs released during a single spawning act and buried successfully in the spawning redd following pair spawning was greater than that following spawning with surrounding individuals. More eggs were also found in the spawning redd after the female rotated. Eggs were buried 0-14 cm deep in spawning redds, those resulting from pair spawning being deeper than those from spawning with surrounding individuals. Larvae emerged around midnight from the spawning redd 7-8 days after spawning, emergence continuing for 3-5 days. Females were consid-ered to reduce the risk of egg cannibalism by spawning many times per day, mid-night emergence of larvae also being important for avoiding predation.