Comparison of Microbial Phytase and Dicalcium Phosphate for Growth and Bone Mineralization of Pond-Raised Channel Catfish, Ictalurus punctatus

Abstract

This study evaluated the use of microbial phytase as replacement for inorganic phosphorus supplement in diets for pond-raised channel catfish, Ictalurus punctatus. Channel catfish fingerlings (average weight: 23 g) were stocked into twelve 0.04-ha ponds at a rate of 18,525 fish/ha. Four ponds were used for each treatment. Fish were fed one of three experimental diets containing 250 or 500 FTU (phytase unit) phytase/kg, or 0.75% dicalcium phosphate once daily to satiation from May to October, 2000. No differences were observed in diet consumption, weight gain, feed conversion ratio, survival, or bone ash and phosphorus concentrations among fish fed different diets. Based on these results it appears that a phytase concentration of 250 FTU/kg diet applied post-pelleting can replace the dicalcium phosphate supplement in channel catfish diets without affecting fish growth and bone mineralization under pond culture conditions. We recommend that a phytase level of 500 FTU/kg diet be used and that the diet contain a total phosphorus level of 0.6% or above to ensure that adequate amount of phosphorus is available to channel catfish. Based on current prices of phytase and inorganic phosphorus sources, it is economical to use phytase in catfish diets.