The First Spawn-taking from Broodstock Yellowtail Cultured with Extruded Dry Pellets

Abstract

This experiment was conducted to gather some basic information necessary for the development of quality dry pellets for yellowtail broodstock. The spawning results of yellowtail broodstock fed soft-dry pellets (SDP) and Oregon type of moist pellets (MP) and/or frozen raw fish (RF) were compared. Yellowtail having an average body weight of 3.7 kg, which had been cultured with extruded dry pellets (EP) from juvenile stage (about 0.89 g BW) for 20 months, were divided into two lots of 25 fish each and stocked into the 5 x 5 x 5 m floating net cages. The first group was fed SDP containing 10% krill meal and the second group was fed MP. Yet another lot of 25 broodstock fish which had been fed EP for 14 months and subsequently fed RF for 6 months, continued to receive the same food until spawning manipulation. Egg collection was undertaken after brood fish were transferred to the 65 m3 spawning tanks on land and they were induced to spawn by injecting 600 IU-HCG/kg-fish BW. Two days after HCG injection, brood fish from SDP and MP groups started to spawn and continued for 8 and 10 days, respectively, but broodstock fed RF spawned only once during this period. The SDP group produced only half of the total number of eggs obtained from the MP group. However, the quality of eggs were found to be superior to those obtained from the MP group. Out of the total eggs produced, the percentages of buoyant and fertilized eggs and total hatch were respectively about 59, 57 and 47 for the SDP group; 39, 34 and 18 for the MP group and 36, 3 and - (not determined) for the RF group. The preliminary results obtained in this experiment have clearly indicated that broodstock yellowtail can be cultured with extruded dry pellets from the juvenile stage under captivity. Further this would enable the development of quality dry pellets for yellowtail broodstock in the near future.