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Abstract, Department of Fisheries, Federal University of Technology, PMB 704 Akure, Nigeria, 

Jackbean (Canavalia ensiformis) seeds were detoxified using six different wet thermal processing (detoxification) methods either in distilled water or 5% (wt./vol.) or trona (NaCO2.NaHCO3.2H2O) solution. The effects of the six detoxification methods on hemagglutinating, antitryptic and urease activities, and on the digestibility coefficient of crude protein and gross energy in the jackbean seeds were investigated. Cracked jackbean seeds cooked (100o C) in trona solution for one hour proved to be more effective as a method of inactivating the anti-nutritional factors in jackbean seeds. Dry detoxified jackbean seed meals derived from cracked jackbean seeds cooked in distilled water or trona solution were later incorporated as protein source in dry practical diets (300 g crude protein, 100 crude lipid and 18.0 MJ gross energy/kg diet) providing 20% or 30% of total protein and fed to Nile tilapia (Oreochromis niloticus) fingerlings (mean weight, 6.7 g) twice daily to apparent satiation for 70 days. Mortality was low (< 5%) and no abnormal fish behaviour was noted even when the detoxified jackbean meals provided 30% of total protein in diet. Growth and feed utilization indices were similar (P > 0.05) in O. niloticus fingerlings fed diets in which cracked jackbean seeds cooked in water provided 20% of total protein and in diets in which cracked jackbean seeds cooked in trona solution provided 20% or 30% of total protein. Carcass composition and hepatosomatic index showed no definite trend among O. niloticus fingerlings fed the experimental diets.