Reproductive biology of Trematomus hansoni (Nototheniidae) in the West Antarctic Peninsula reveals inshore spawning

Abstract

Understanding the reproductive strategies of Antarctic notothenioids is essential for assessing their vulnerability to environmental change. This study provides evidence of inshore spawning in the striped notothen Trematomus hansoni off the West Antarctic Peninsula (WAP), based on macroscopic and histological analyses of gonads from specimens collected in Paradise Bay during austral summer 2019, 2023 and 2025. Gravid females display a group-synchronous ovarian development organization and a total spawning strategy, releasing large yolkedoocytes (2.1–4.7 mm) in a single event during the spawning season. Post-ovulatory follicles and hydrated oocyte expulsion confirm that spawning occurs in late January–February in shallow coastal waters. The simultaneous presence of ripe males with mature spermatozoa indicates a synchronous reproductive period. The positive allometric growth observed in T. hansoni suggests a capital breeding strategy, consistent with ecological adaptations to the highly seasonal polar environment. Reproductive traits closely matched values from other Antarcticpopulations, although regional differences were observed in fecundity and gonadal investment. Our results align with documented evidence that several notothenioids species use nearshore habitats for reproduction. Given the WAP status as one of the fastest-warming regions on Earth, these findings highlight the ecological significance and vulnerability of inshore habitats. As temperature-driven changes may disrupt spawning timing and success, long-term monitoring of reproductive patterns is essential. The present study also underscores the need to consider inshore ecosystems in Antarctic fish population’s conservation and management efforts.