First evidence of gastric brooding in Asterinidae highlighted by the reproductive strategy of Asterina fimbriata in Atlantic Patagonia

The reproductive biology of Asterina fimbriata , a member of the family Asterinidae, was investigated through monthly sampling between July 2021 and June 2023 in Atlantic Patagonian coastal waters. This species presented a curious reproduction strategy: females exhibited an aperiodic reproductive pattern, characterized by the continuous presence of oocytes at different developmental stages co-occurring within the gonads and a low frequency of mature oocytes along the year. However, 6.52% of females exhibited a periodic oogenic cycle, showing a release maximum peak between May and September (coldest water temperature) Males displayed a clear annual gametogenic cycle, with maximum sperm release during the coldest months (June-August). Only 8% of females exhibiting brooding behaviour, which lasted approximately four months (May-September) and coincides after the major oocyte release season. Broods developed within the stomach and, following metamorphosis, emerged as a mass outside the female's mouth. Six distinct developmental stages were identified, revealing a progressive transition from internal to external brooding as offspring matured. A. fimbriata represents the first confirmed case of gastric brooding in the family Asterinidae. The low proportion of reproductive females would be indicating a high energetic cost of incubation that could be associated to the feeding behaviour of this fragile species. These findings expand the understanding of reproductive strategies in sea stars and highlight a novel adaptation within this clade.