HORMONAL INDUCED SPAWNING OF CAPTIVE SILVER THERAPON Leiopotherapon plumbeus (KNER, 1864)

Silver therapon (Leiopotherapon plumbeus, Kner 1864) is a small endemic silver-colored fish used to be plentiful in the Philippine freshwater bodies (Figure 1). Its tasty flesh is popularized making this as one of the most expensive edible freshwater fish in the country. However, it is now considered an endangered species and dwindling due to overfishing of local fishermen and presence of invasive species.

The issue on conservation of wild L. plumbeus has resulted in an increased effort and research endeavors in the development of techniques and technology for hatchery production for this fish. However, there has been no induced spawning trial that has been done for this fish species. Hence, the main objective of the study was to induce spawn the L. plumbeus using human chorionic gonadotropin (hCG) and to document reproductive parameters including spawning time, gonadosomatic index, fertilization, and hatching rate.

Broodstock (14.11 ± 1.05 g males, 15.85 ± 2.05 g females at a sex ratio of 1 male: 1 female) were injected with 4 IU hCG g^-1 BW and held in 20-L spawning aquarium. Water temperature in tanks were about 27.2-28.3°C. Females from five out of nine pairs were spawned, with estimated fertilized eggs of approximately 5,000-6,500 adhesive eggs per female. Spawning time was observed to be from 18 to 24 h after injection. Fertilization rate varied from 75.0-91.11%, whilst hatching rate ranged from 94.44-100%. Fertilized eggs were 0.98 ± 0.09 mm in diameter, which exhibited meroblastic development. Hatching occurred from 20-28 h post fertilization, producing yolksac larvae of with a total length of 1.19-2.34 mm (mean = 1.98 mm). The larvae have large elliptical yolk, comprising about 39-42% of the larvae total length. Yolk was completely absorbed in most specimens after day-3 post hatching.