Bhujel, Ram C. creator Yakupitiyage, Amararatne Chairperson Little, David C. Examination Committee Tang, John C.S. Examination Committee Lin, Chang Kwei Examination Committee Phelps, Ronald P. Examination Committee Narai Technologies Co. Ltd., Nam Sai Farm Co. Ltd., and Self support Scholarship donor text series technical report th Bangkok Asian Institute of Technology 1999 continuing eng 175 leaves Seven on-farm trials were conducted at Nam Sai Farm, a commercial tilapia hatchery located at Ban Sang district in Prachinburi Province of Thailand. The main objective of these trials was to develop guidelines for the efficient management of Nile tilapia broodfish. The research area included feed selection, hapa exchange, hapa design, environmental manipulation, spawning synchronization and broodfish selection. The first trial with three locally available commercial feeds showed that broodfish fed with two catfish pellets containing 25% and 30% CP diets produced 27% and 30% more (P<0.05) seed than 15.5% CP herbivorous feed respectively. The cost/seed was lowest from 25% CP catfish pellet. In trial 2, existing and high feeding rates (0.7% and 1.4% biomass.dai 1 respectively) were compared for three hapa exchange intervals. The high feeding rate produced 16% more (P<0.05) seed as compared to the existing rate and resulted in lower cost of production per seed. Hapa exchange interval of 15 and 60 days produced 14% and 13% more (P<0.05) seed as compared to the 5-day exchange. The low seed output in 5-day exchange was due to more loss of females. In trial 3, efficacy of a modified hapa design was tested over the existing hapa design. Seed output from modified hapas was 30% more with 23% reduction in the cost of production per seed compared with the old design. Trial 4 was conducted in hapas (l.4m x l.4m) installed in sunken tanks (2 m. dia.). It showed that Nile tilapia females bred in the tanks containing water cooled with ice (174 ± 16 seed.m-2 .d-1 ) and shade (56±2 seed.m-2 .d 1 ) produced 7.5 and 2.4 times more seed respectively, as compared to the control (23 ± 8 seed.m 2 .d 1 ). Aeration gave more variable results while salinity and water depths gave poorer results. Seed output linearly decreased at >29°C afternoon water temperature approaching to nil at ;;:::34°C. Maximum seed output occurred at 2-3mg/L early morning DO with complete stoppage at ~0 .5 mg/L. Cooling of water with ice was prohibitively expensive, while shading and aeration were relatively affordable and applicable for the hapa-in pond system. In Trial 5, sprinkling, shade and aeration were tested in hapa-in-tank and hapa-in-pond systems. In tanks, seed output from control treatment was higher than from shade and similar with sprinkling treatment. Unexpected heavy and frequent rainfall during this trial might have masked the effects of shade and sprinkling favoring the control treatment. However, the preliminary trial in pond showed 47%, 17% and 56% increased seed output from sprinkling, shade and their combinations respectively over the control. Nevertheless, this trial showed that sprinkling and shading are applicable and cost-effective temperature control measures. Trial 6 consisted of spawning synchronization and female selection. Both were conducted in hapas (120 m2 ) installed in a pond (- 0.5 ha). The peak spawning intensity was obtained on the 20th day. Broodfish selection trial showed that one fourth (25%) of the total number of females (5,980) did not spawn at all within 35 days even if they were continuously kept in spawning hapas together with mature males. The 2-time spawner (2-S) and 1-time spawner (1-S) groups (126±22 and 106± 15 seed.m-2 .d 1 respectively) produced 78% and 49% more seed output (P<0.05) respectively compared with the late spawner (0-S) group (71±7 seed.m-2 .d-1 ). However, the clutches and seed outputs after 4th seed harvest cycle were similar in all the groups. Cost of production per seed was 62% and 14% less from 2- and I-time spawners respectively as compared to the later spawners. A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science (D. Tech. Sc.), School of Environment, Resources and Development Thesis (Ph.D.) - Asian Institute of Technology,1999 Nile tilapia Thailand Fishes Breeding Thailand Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B11869 http://203.159.5.9/ait-thesis/detail.php?q=B11869 191200 20260818154037.0