Hermaphroditism and Sex Reversal in Fishes of the Platycephalidae-III.Variation in the Mode of Sex Reversal and Speciation

Abstract

Among platycephalid fishes, transition on sexuality from hermaphroditism to gonochorism is recognized paralleled with the patterns of morphological changes of gonads accompanied by protandrous sex reversal.Here, the speciation of platycephalid fishes was reexamined on the basis of the taxonomic study of Matsubara and Ochiai (1955), considering a few additional characters.As a result, it became clear that declination of the hermaphroditic nature corresponds to the process of the speciation.
Generally two directions were recognized in this process;one is toward specialization and gave rise to fishes of the subfamily Onigociinae, and another is toward largesize and brought about the subfamilies Inegociinae and Platycephalinae.It was considered that the genus, Kumococius, lies at the center of speciation of these groups, since the species of this genus retains a few relic characters of nektonic life, such as absence of the nasal flap;the slightly concave pectoral fin along the posterior margin; and small, less degenerated gas bladder.As species become more specialized, hermaphroditism tends to decrease.From this, the ancestor of the platycephalid fishes might be considered synchronously hermaphroditic carrying a marked hermaphroditic nature.
It is known that the transitional trend from hermaphroditism to gonochorism also exists in the Serranidae and Sparidae, as well as in the Platycephalidae.Structures of representative hermaphroditic gonads of these families are judged to be similar to that of synchronous hermaphrodite, as well as the Serranidae.From this it was considered that hermaphroditism of at least these three families have a common evolutional foundation and that hermaphroditism might have been the original condition in these fishes.