Studies on the early life history of two Platycephalus fishes distributed in Ariake Sound

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On two Platycephalus fishes distributed in Ariake Sound, the discrimination of species in young stages, age and growth, maturation, early morphology, early ecology, and low salinity tolerance were investigated. Studies on the age and growth resulted in the determination of the Bertalanffy's growth equation for each species, and studies on their reproduction determined the spawning season and the spawning ground of each species. The rearing experiments of their eggs and larvae elucidated the morphological developments in egg, larval and juvenile stages of both species, and established the method of seedling production. Although the morphological comparison of larvae and juveniles between species in young stages failed in the discrimination of a-species from each other, a PRC RFLP analysis technique established in this study was successful in discriminating a species from each other. The field surveys in various surf areas in Ariake Sound have found that the mouth areas of rivers, which discharge themselves into the eastern part of Ariake sound, are used by a species of Platycephalus (so-called magochi in Japanese) as their nursery. The juveniles come to the sandy bottom of the river mouths, and stay there for about one year. A comparison of the tolerance to low salinity between juveniles of both species revealed that the species of Platycephalus (so called magochi) is more tolerant to low salinity than the other species (so-called yoshinogochi).