マシジミの生態に関する研究-3-周年性産卵と生殖巣内自家受精について

概要

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This study was performed to investigate whether Corbicula leana, a fresh-water hermaphroditic bivalve known to spawn during March and November, spawn even in the winter season. Incubated young were found within the inner demibranchs in some of the individuals collected in a culture pond in Kobayashi City on December 19. 1975, February 24, 1976 and March 25, 1976. In February, 17 of 150 specimens were incubating young, and the number of the young in each individual ranged between 32 and 870. Histological observation of the gonads (ovotestes) during June 1975 and April 1976 revealed that all the individuals observed held mature gametes regardless of the time of collection. Percentage of the maturation stage-oocytes measuring above 130μ in long axis in all the oocytes of more than 15-20×25-30μ varied widely from individual to individual independently of the seasons: for instance, 9.9-21.2% in January, 13.2-20.7% in April, 5.7-18.0% in August. Percentage in an individual fixed immediately before spawning began was 33.7%. It is concluded that Corbicula leana, as a population, may spawn throughout the year though the individuals may spawn out of step. This study also revealed the presence of self-fertilized ova in cleavage within the gonads.