<![CDATA[Sintasan larva hingga benih ikan tuna sirip kuning di hatchery sudah meningkat dari 0,05% menjadi 0,20%-0,50%. Namun mortalitas pada pemeliharaan tahap berikutnya sangat tinggi. Kematian benih karena menabrak dinding bak/jaring, berkaitan dengan kebiasaan renang dan kondisi lingkungan. Oleh karena itu, riset pendederan ini difokuskan pada pengamatan kebiasaan berenang dan pemangsaan, serta kondisi lingkungan. Wadah yang digunakan adalah enam buah bak fiberglass reinforced plastic (FRP) diameter 2,7 m; ketinggian 1,0 m; dan diisi dengan air laut 5 m3. Hewan uji berupa benih ikan tuna sirip kuning dengan panjang total 29,82 ± 2,51 mm hasil produksi dari hatchery, sebanyak 50 ekor benih per bak. Perlakuan dalam riset adalah perbedaan sistem pemeliharaan, yaitu: (A) indoor dan (B) outdoor dengan tiga ulangan dan lama penelitian 21 hari. Pakan yang digunakan adalah ikan segar berupa benih bandeng yang dimatikan dan ikan teri dengan panjang total 15-25 mm dan ikan cincang (minced fish). Frekuensi pemberian pakan adalah enam kali per hari dan diberikan secara satiasi. Parameter meliputi suhu, oksigen terlarut, dan intensitas cahaya diukur setiap hari. Hasil riset menunjukkan bahwa sintasan dalam pendederan sistem indoor sebesar 20,0 ± 4,0% lebih tinggi (P<0,05) dibanding dengan sistem outdoor (6,7 ± 5,0%). Pertumbuhan bobot spesifik 12,4% hari-1 pada sistem indoor lebih baik dibandingkan sistem outdoor yang hanya 9,8% hari-1 (P<0,05). Dari hasil penelitian ini dapat disimpulkan bahwa intensitas cahaya dan suhu yang lebih stabil pada pendederan sistem indoor memberikan sintasan dan pertumbuhan yang lebih baik dibandingkan pada sistem outdoor. Namun demikian, disarankan bahwa pendederan dalam bak FRP sebaiknya tidak lebih dari dua minggu agar diperoleh sintasan yang lebih tinggi dan selanjutnya dipindahkan ke karamba jaring apung (KJA).The survival rate of reared yellowfin tuna from larvae to juvenile stages in hatchery has been improved from 0.05% to 0.20%-0.50%. Unfortunately, the fish’s mortality rate during the nursery phase is still very high. Unpredicted swimming and feeding behaviors have resulted the reared juveniles to uncontrollably hit the tank wall and died. Therefore, this research was carried out to study the swimming and feeding habits of yellowfin tuna juveniles and its response to different rearing environments. Six fiberglass reinforced plastic (FRP) tanks with a diameter of 2.7 m, height 1.0 m, and filled with 5 m3 of filtered sea water were used in the study. Yellowfin tuna juveniles with an average total length of 29.82 ± 2.51 mm were harvested from a hatchery and placed into each tank at a density of 50 fish tank-1. The treatments applied were two nursery systems: (A) indoor and (B) outdoor system with three replicates. The rearing treatment lasted for 21 days. Raw fish was given as feed consisting of mixed of defrosted milkfish fry and small anchovy with total length ranged between 15-25 mm as well as minced fish meat. Feed was given six times per day at satiation. The observed parameters were temperature, dissolved oxygen, and light intensity measured daily. The results showed that the survival rate of juvenile in the indoor system was 20.0 ± 4.0%, which was higher (P<0.05) than that of the outdoor system (6.7 ± 5.0%). Weight specific growth rate of fish reared in the indoor system was 12.4% day-1 which was better than that of the outdoor system which was only 9.8% day-1 (P<0.05). This research concludes that a stable light intensity and water temperature in the indoor nursery system gives better survival and growth rate on yellowfin tuna juvenile. Nevertheless, this research recommends that the nursery phase of yellowfin tuna juvenile in FRP tank should be carried out not more than two weeks in order to produce a higher survival rate and then transferred to floating net cages.]]>
