Morphology and Ultrastructure of Puye (Galaxias maculatus) Spermatozoa

This study characterises basic seminal and sperm parameters of puye ( Galaxias maculatus maculatus ), including sperm concentration, seminal plasma osmolality and cell viability. In addition, it provides a detailed description of sperm ultrastructure. Wild males ( n = 21) were captured in southern Chile. A small and variable volume of milt was collected per male; the samples exhibited a high sperm concentration (55.84 ± 8.25 × 10 9 spermatozoa mL −1 ) and high viability (94.38% ± 2.78%). Spermatozoa had a total length of 26.9 ± 0.63 μm and consisted of an elongated head lacking an acrosome, a short mid‐piece with ring‐shaped mitochondrion, and a relatively short flagellum. The nucleus contained a deep nuclear fossa occupying almost the entire head, from which the flagellum emerged. The flagellum exhibits the classical 9 + 2 axoneme structure and consists of a long main piece and a short end‐piece. The main piece presents a pair of side‐fins of variable length, oriented in the plane of the central microtubules. This study provides the first detailed description of sperm ultrastructure in G. maculatus , revealing similarities with various fish families. This information could be valuable for future research on reproductive physiology, sperm evolution and potential applications in assisted reproduction and conservation.