Ovarian development and reproductive biology of Hoplias argentinensis (Characiformes: Erythrinidae), a top predator of the Pampa plain lakes, Argentina

Abstract Species in the Hoplias malabaricus complex are important for commercial and artisanal fisheries. Recent studies have identified several species within this complex, including Hoplias argentinensis (the southernmost species), but no precise biological knowledge exist for it. In the present work, the reproductive biology of H. argentinensis was studied in the shallow lake Kakel Huincul (Buenos Aires, Argentina), between May 2022 and May 2023. Five ovarian maturation phases were macroscopic and histologically characterized and four ovarian maturation phases were detected: immature, developing, spawning capable (including active spawning subphase) and regressing. The results suggest a reproductive season from May to February, with a spawning season from October to February. Batch fecundity varied between 24,342 and 77,866 oocytes. The relative fecundity ranged between 12 and 67 oocytes/g ovary. Histological analysis and frequency distribution of oocyte diameters in actively spawning females revealed a tetramodal pattern characterizing H. argentinensis as an iteroparous batch spawner with indeterminate fecundity. These results provide a better understanding of the reproductive life cycle of this newly described species at its southernmost occurrence. This study also provides the first histologic description of the maturation ovarian phases and oocyte development stages in an annual cycle.