琵琶湖におけるイサザ仔魚の生活

抄録

To know the life of Isaza Chaenogobius isaza in larval stage, observations at the spawning grounds, attempts of raising larvae and offshore towing survey were carried out. Only the yolksac larvae just after hatching were found at the spawning ground. Observations on varous spawning grounds did not show the presence of definite species of organisms regarded as food for the larvae. The larvae kept in aquaria did not feed on organisms collected at spawning grounds. On the other hand, six Isaza larvae in the process of developing fin rays (6.1-10.7mm SL) were caught by offshore towing. These larvae fed exclusively on Eodiaptomus japonicus which is distributed offshore despite the amount of E.japonicus was smaller than that of other zooplankters. From all these facts and that the newly hatched yolk-sac larvae in an aquarium have been observed to swim up vertically to the surface of water, the yolk-sac larvae hatching out at the spawning ground were assumed to swim up to the water surfae immediately and to be carried offshore drifted by water current. Isaza larvae apper to distinguish and choose E.japonicus from the others.