Milt Characterization and Sperm Structure of the Parassi Mullet Mugil incilis, Hancock, 1830

Parassi mullet (Mugil incilis) is an ecologically and economically important species that supports small-scale artisanal fisheries. However, scarce knowledge of its reproductive biology limits the development of management and conservation strategies. This research describes key milt and sperm characteristics, including milt volume, sperm concentration, motility, and ultrastructural features. Males produced an average of 40.0 ± 20 µL of milt, with sperm concentrations between 6.00 and 20.37 × 109 spermatozoa mL−1. Sperm motility varied between 10% and 80%, with a mean duration of 14.13 ± 4.49 min. Mature spermatozoa measured 33.79 ± 0.67 µm and exhibited a subspherical head without an acrosome, a short midpiece, and a cylindrical flagellum. The nucleus contains electron-dense heterogeneous chromatin. The centriolar complex was positioned outside the nuclear fossa consistent with Type II spermiogenesis. The flagellum comprises a main piece and tapering end piece. The axoneme had 9 + 0 arrangement at the basal body region and the typical 9 + 2 configuration along its length. These results provide the first detailed description of sperm morphology in parassi mullet and contribute to an understanding of its reproductive biology, supporting future applications in taxonomy, toxicology, conservation and aquaculture programs.