Variations in Gonadosomatic Index, Gonadal Development and Spawning Induction of Spotted Scat Scatophagus argus (Linnaeus, 1766)

This study evaluated variations in gonadosomatic index (GSI), gonadal development stages, and hormonal spawning induction of Scatophagus argus in captivity. Male and female fish were cultured separately in net cages in Tam Giang lagoon, Central Vietnam, from January to December 2020. Five fish of each sex were randomly sampled monthly. Gonads were collected, GSI determined, and subsequently prepared for histology. Gamete quality was assessed with a light microscope. Spawning was hormonally induced with different doses of human chorionic gonadotropin (hCG) and luteinizing hormone-release hormone (LHRH-A2). Gonadal development started to increase in March, peaking in July. The peak spawning period of the fish was from June to August, displaying the highest GSI value, sperm motility, and oocyte diameter. Only female GSI fluctuated significantly month-by-month (P<0.05). Histological examination indicated that S. argus is a multiple-spawner. Application of LHRH-A2 (70 µg/kg) stimulated spawning and resulted in better latency periods, fertilization, and hatching rates.