Sexual dimorphism and protogeny in two species of Selenanthias (Serranidae: Anthiadinae) collected from Japanese waters

Abstract Sex changes in fish are commonly driven by social or reproductive advantages associated with body size, and protogyny is particularly prevalent in species exhibiting male territoriality or haremic mating systems. Within the family Serranidae, several species exhibit sexual dimorphism and protogyny; however, in the genus Selenanthias , only Selenanthias analis Tanaka 1918 has been reported to exhibit sexual dimorphism. The present study investigated sexual dimorphism and the occurrence of protogynous hermaphroditism in two serranid species, S. analis and Selenanthias sp. sensu Ikeda and Nakabo 2015, based on external morphology, gonadal histology, and mitochondrial DNA sequences (partial COI region). Morphological and histological analyses revealed consistent sex-specific coloration and differences in the fin filament lengths in both species. Six individuals of S. analis possessed gonads containing both ovarian and testicular tissues. Among these, two individuals morphologically identified as males and four individuals represented both female and male characteristics. In addition to these six individuals, two individuals exhibited both female and male morphological characteristics but possessed only ovarian tissue. Genetic analyses supported the recognition of two distinct species ( S. analis and Selenanthias sp.) and confirmed that the color morphs within each species represent intraspecific sexual dimorphism. These findings provide the first evidence of sex change in the genus Selenanthias , establishing S. analis as a protogynous species and suggesting a similar potential for sex change in Selenanthias sp.