Performance of yellowfin tuna spawning (Thunnus albacares) in floating net cage

Yellowfin tuna ( Thunnus albacares ) is an important export commodity in Indonesia. This tuna has an important economic value, so it becomes one of the foreign exchange that can provide solutions to the national economy. Yellowfin tuna hatchery technology that was carried out at the Research Institute for Mariculture and Fisheries Extension, with the management of broodstock maintenance in floating net cages has successfully spawned. However, the quality and quantity of eggs produced are still not optimal. This research was conducted in floating net cage with a diameter of 48.8 m with a depth of 8 meters, filled with 30 fishes of yellowfin tuna with body weights ranging from 60-80 kg per fish. Feed given is: fresh fish, squid and added vitamin C and vitamin E. The parameters observed were : spawning frequency, number of eggs produced, hatching rate, egg diameter, diameter of oil globule and the survival activity index value of newly hatched larvae (SAI). As supporting data, water quality observations were carried out which included: temperature, salinity, and water brightness on the floating net cage. This research was conducted for 10 months, from January to October 2019. Data analysis was carried out in discriptively. The results showed that yellowfin tuna reared in floating net cage can spawn well. Spawning occurs every month. The highest spawning frequency in October is 20 times spawning. While the highest total number of eggs successfully harvested was 11,030,000 eggs in August. Hatching rate between 70.5-92.2%. The survival activity index of newly hatched larvae (SAI) is 2.4-3.7