バラタナゴRhodeus ocellatus(kner)の産卵効率に影響する要因に関する実験的解析

type:Article

バラタナゴの繁殖行動の頻度,産卵様式,そして貝に産み込まれる卵数(産卵数)に影響する要因を実験的に解析しようとした。魚の密度が高くなると,なわばり雄は貝を防衛する行動を高頻度に行うために,番形成の継続時間は短くなる。そして,番産卵の頻度は減少し,集団産卵が増加する。イシガイの密度と分布様式を一定にしておくと,魚の密度の増加につれて産卵数も比例的に増加する。また,貝の密度の増加や貝の集中によって貝間の距離が短かくなると,魚の密度が一定であれば,産卵数は増加する。

The factors controlling frequency of reproductive activities, mode of spawning and number of eggs laid by the bitterling, Rhodeus ocellatus (Kner)were analyzed under laboratory conditions. Body length of the territorial males was relatively larger than that of non-territorial ones. The duration of holding a courtship is shortened when the population density of the males increases, because in such a case the male obliged to defend his territory more frequently. As the results, pair spawning becomes infrequent, instead group spawning being frequently performed by many males and females. Under the experimental conditions in which the density and distribution pattern of host bivalve, Unio douglasiae Griffith and Pidgeon is constant, the number of eggs of the bitterling seemed to proportionally increase with increase of the spawner density. Distance between a closest pair of bivalves seemed to affect spawning efficiency, that is, the shorter the distance was, the more eggs were laid. This may probably be caused by increased occurrence of group spawnig. Such process as above caused by shortening the distance as a result of increasing in the density of bivalves which are uniformly distributed and also as a result of aggregation of bivalves. The causation and its ecological significance are discussed.