USE OF MICROBIAL PHYTASE IN CHANNEL CATFISH ICTALURUS-PUNCTATUS DIETSTO IMPROVE UTILIZATION OF PHYTATE PHOSPHORUS

A 10-wk feeding trial was conducted in the laboratory during which cha nnel catfish Ictalurus punctatus (average initial weight: 6.5 g/fish) were fed five practical diets containing either 0, 500, 1,000, 2,000, or 4,000 units of microbial phytase/kg diet, Fish fed diets containing 500 or more units of microbial phytase/kg consumed more feed and gain ed more weight than fish fed the basal diet without supplemental phyta se. Feed conversion ratios (FCR) did not differ among treatments excep t the FCR for fish fed 1,000 units of microbial phytase/kg diet was lo wer than that of fish fed no supplemental phytase. Fish survival was n ot different among treatments. Contrast analysis showed that weight ga in, feed consumption, bone ash, and bone phosphorus were higher and fe ed conversion ratio was lower for fish fed diets supplemented with phy tase as compared to fish fed no supplemental phytase. The concentratio n of fecal phosphorus decreased linearly as phytase supplementation in creased. Results from this study demonstrate that microbial phytase is effective in improving bioavailability of phytate phosphorus to chann el catfish, which may eventually lead to a reduction in the amount of supplemental phosphorus added to commercial channel catfish feeds.