Evidence of occurrence of intersex in Indo-Pacific sergeant, Abudefduf vaigiensis

Abstract

The gonadal morphology and reproductive strategy of Abudefduf vaigiensis, a reef-associated damselfish, collected from Maraikayar Pattinam, Mandapam, Tamil Nadu, India, was investigated. A total of 120 specimens were examined through gross anatomical and histological analyses to assess gonadal structure and sexual characteristics. Among the 110 mature fish (70 males and 40 females; 10–15 cm TL), 4 individuals (10–12 cm TL) exhibited intersex gonads; 10 were unsexed. Typical gonochoristic features were recorded in both sexes in many of the cases (92%), whilst other fishes were found with immature gonads. Mature testes appeared bilobed and asymmetrical, with histological sections revealing active spermatogenesis and well-defined seminiferous lobules. Ovaries exhibited asynchronous development, containing vitellogenic, lipid vesicles, and perinuclear oocytes, suggesting batch spawning potential. Intersex gonads displaying testicular tissue distributed in the developing ovarian lobe were identified and confirmed histologically. This indicates the first histological evidence of intersex in this species. These findings challenge the previously held assumption of strict gonochorism in Abudefduf spp. and highlight the need for broader temporal and spatial sampling to understand the ecological and captive breeding implications of reproductive plasticity in this taxon. The results indicated the presence of either a sequential hermaphroditism or potential endocrine disruption in the species