Suchart Ingthamjitr creator Demaine, Harvey Chairperson Macintosh, Donald J. Examination committee Johri, Lalit M. Examination Committee Boonjit Titapiwatanakun Examination committee Little, David C. Examination Committee Overseas Development Administration (U.K.) Scholarship donor text series technical report th Bangkok Asian Institute of Technology 1997 continuing eng 135 leaves Hybrid CIarr'as cat{uFB01}sh (CIan'as macrocephabrs x C [arias garieprrms) is a cultured {uFB01}sh of major economic importance in Thailand. Culture of Thai native cat{uFB01}sh became established over 30 years ago, but introduction of the hybrid in the late 1980's revolutionized the scale and importance of the industry. Recently, farmers raising the hybrid cat{uFB01}sh have been faced with slow growth and poor survival of their stocked {uFB01}sh, in addition to high competition and low pro{uFB01}t margins. Initial surveys traced some of these problems to hatchery practices and led to a research framework to analyze the technical and economic status of cat{uFB01}sh hatcheries. The study focused on cat{uFB01}sh hatcheries in central Thailand and based analysis on technical, economic and social data collected between April 1995 to May 1996 from thirty hatcheries. Fry were assessed for quality during the early and mid-spawning season from different hatcheries using a salinity challenge stress test. A clear dichotomy of scale was observed in hatchery operations in central Thailand based on annual production (de{uFB01}ned as small<73 million or large>73 million cat{uFB01}sh fry). A major center of cat{uFB01}sh hatcheries was found to be Nong Kae district in Sara Buri province and Nong Sua district in Pathum Thani province. The relative advantage of this area was its proximity to both a major source of female brood{uFB01}sh (Clarias macrocephalus) and live feed (Moina macrocopa). Female brood{uFB01}sh used to produce hybrid Clarias fry are mainly from Trichogaster culture farms in Chachoengsao and Samutprakarn province. The other signi{uFB01}cant factor is the development of mass production of the water {uFB02}ea (Mama macrocopa) pioneered by Pathum Thani Fisheries Development Station. Moina is required by hybrid Cian'as hatcheries in large quantities. Small{u2014}scale hatcheries tended to produce cat{uFB01}sh fry as a part-time activity, relying on purchased female brood{uFB01}sh whereas larger hatcheries were full-time and often produced their own brood{uFB01}sh. Although many hatcheries produced fry during the cool season (October to January), only 3 hatcheries produced fry year-round. Gonadotropic-releasing hormones were the most popular class of hormone used to stimulate ovulation, partly due to the effectiveness of a single injection. However, some larger hatcheries continued to use whole pituitary glands, claiming that better quality fry as a result. Technologies used to incubate fertilized eggs and larvae were similar irrespective of the hormone used. Application of a Cobb-Douglas production function identi{uFB01}ed female brood{uFB01}sh biomass used as the dominant explanatory variable for fry production; this input made up between 79{u2014} 87 percent of variable costs. Break-even analysis indicated that small-scale hatcheries had lower efficiencies of production than large-scale ones. Marketing of fry by hatcheries was sophisticated, involving their direct marketing to food {uFB01}sh farmers. or via middlemen and nurseries. Fierce competition has stimulated hatcheries to offer free transportation or live feeds to customers buying large numbers of seed. A challenge stress test was developed based on survival of yolk-sac fry at a salinity of 12 ppt. over a 60 minute period. Survival was compared to performance over a period of nursing. Fry quality was found to vary greatly with season; poorest quality fry were produced early in the year. Seed quality tests indicated superior quality fry were produced from female brood{uFB01}sh maintained and conditioned within the hatchery rather than from {uFB01}sh purchased and spawned immediately. The use of stress tests by hatcheries and their customers could enable them to identify poor quality fry at purchase; this could reduce the costs and risks attached to hybrid cat{uFB01}sh production considerably. A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Technical Science, School of Environment, Resources and Development Thesis (Ph.D.) - Asian Institute of Technology, 1997 Fish-culture Thailand, Central Catfishes Thailand, Central Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B00356 http://203.159.5.9/ait-thesis/detail.php?q=B00356 020998 20260818133954.0