Organized by Graduate School of Informatics, Kyoto University ; JSPS Bangkok Liaison Office ; Japanese Society of Bio-logging Science ; Informatics Research Center for Development of Knowledge Society InfrastructureDecember 13-14, 2005, Siam City Hotel, Bangkok, ThailandWe studied the feeding habits of the hatchery-reared young Mekong giant catfish released in a fish pond and Mae peum reservoir, northern Thailand. We examined the gut (stomach and intestine) contents of 5 catfish, Relative Length of Gut (RLG) of 4 catfish and plankton composition in the reservoir. The gut contents of the catfish in the fish pond consisted of a fluid like the pellets, zooplankton, phytoplankton and aquatic plants. The gut contents in the reservoir consisted of unspecified contents, zooplankton and phytoplankton. The majority of prey items were the Branchiopoda (75 % in zooplankton) and Chlorophyceae (98 % in phytoplankton) in the gut contents of the catfish in the reservoir, while the major plankton in the reservoir were copepoda including nauplius and copepodid (mean : 50 %) and eurotatorea (mean : 41 %) in zooplankton, and chrysophyceae (mean : 52 %) and chlorophyceae (mean : 38 %) in phytoplankton. It is reasonable to suppose that the catfish positively selected their major prey items if a particular prey item was found in the gut contents, contrary to the organism composition in the reservoir. However, the cuticle and the cell walls of these plankton are resistant to intestine enzymes of some fish. Furthermore, RLG of 4 catfish were greater than 1. In general, a fish is carnivorous when RLG is less than 1, while the fish is herbivorous or omnivorous when RLG is greater than 1. These results indicate that the hatchery-reared young catfish fed on the potential prey items in front of the catfish, and the catfish might not be piscivorous but planktivorous
