テナガエビの交尾, 放卵行動について

福山市の芦田川で採集したテナガエビの成熟個体を実験室で飼育することによって、交尾と放卵行動を観察し、産卵婚期中における1個体の産卵回数を推定した。1)産卵期中に体長約6㎜の大型のテナガエビは少なくとも4回以上産卵し、体長約4㎜の中型のテナガエビは少なくとも2固以上産卵する。2)交尾の行われる2日前頃から雌雄は相接近し、雄は雌を追尾する。交尾の2～3時間前に、雌は雄の広げた第2胸脚の間に入る。雄の触角や第1胸脚が雌の体に接触する。雌は脱皮直後に腹面を上に向け、その上に雄が相対し、両者の腹面が接することにより交尾が行われる。3)交尾後6時間以内に産卵が行われる。それから、11～12日の抱卵期間を経て放卵されると同時に、幼生がふ出する。放卵行動は午後7時頃からはじまり、60～90分間続くが、放卵は前半の30～45分間にほぼ完了する。放卵時に雌は腹部を底面に対して約45°斜め後方に向け、数秒間、全腹肢を激しく前後に振動させる。その後、腹部を下ろし、腹肢の振動を止める。このような行動を数十秒から数分間隔で何回も繰り返す。放卵から次の産卵までに要する日数は1～2日であり、この間に雌は脱皮し、交尾を行う。

Two series of the oriental river prawn, Macrobrachiurn nipponense (DE HAAN), females of which were both collected from a river in Fukuyama City, Hiroshima Prefecture, have been reared in the laboratory in order to observe their mating and spawning behaviours. About two days before the mating the male begins to approach and to follow the female. A few hours before the mating the male holds the female between the widely extended second pair of pereiopods and actively touches the female with his antennae and first pair of pereiopods. The mating depends largely upon the pre-mating molt of the female and takes place night and day, immediately after the pre-mating molt. The male turns the soft-shelled female to a ventral side position and then presses down from above for 2-3 seconds. Soon after this, the male separates from the female. This behaviour usually is repeated 2-4 times after a single pre-mating molt. The female lays eggs within 6 hours after mating and carries on the pleopods 11-12 days. The spawning activity begins around 7p.m. and continues for one or one and a half hours. The female raises up the abdomen unto an angle of 45°- 90°against substratum and vibrates vigorously all pairs of pleopods to release the larvae just hatched for a few seconds. Then she returns to the normal posture and stops vibrating the pleopods. This activity is repeated many times during the spawning period at a interval from 20-30 seconds to a few minutes, though almost all larvae hatch out the first 30-45 minutes. A single female lays eggs twice and more in one season. The interval between the release of the larvae and the succeeding egg-laying is one or two days.