Reproductive Biology of Male Blackhand Paradise Fish Polynemus melanochir (Polynemidae) from Southwestern Vietnam

This study examines the reproductive biology of Polynemus melanochir, an economically essential threadfin species inhabiting southwestern Vietnam. A total of 403 male specimens were collected monthly over 12 months to investigate testicular development stages, histological traits, seasonal variation in gonadosomatic index, and size at 50% maturity. Morphological and histological analyses identified four testicular development stages, ranging from immature (stage I), maturing (stages II and III), to mature (stage IV). The frequency of testicular stages and seasonal fluctuations in gonadosomatic index suggested that the species was a multiple-spawner releasing sperm several times during the year-round study, with two reproductive peaks occurring in March (dry season) and September (wet season). The estimated size at 50% maturity was 14.4 cm, providing a scientific basis for defining minimum catch sizes. These findings offer essential baseline data on the reproductive biology of male P. melanochir, which can inform management strategies such as identifying spawning seasons and establishing seasonal and size-based fishing regulations.