Pond-raised Hybrid Catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus, Do Not Respond to Microbial Phytase Superdosing: CATFISH DO NOT RESPOND TO PHYTASE “SUPERDOSING”

Two experiments were conducted in consecutive years to evaluate the responses of hybrid catfish, female Ictalurus punctatus x male Ictalurus furcatus, to "superdosing" of 6-phytase added to existing commercial catfish feeds. In each experiment, two diets with or without a phytase superdose (2500 and 5000 phytase units/kg, respectively) were compared. In Experiment 1, fingerlings (mean weight: 59 g/fish) were stocked in 17 0.4-ha earthen ponds at 17,290 fish/ha and were fed once daily to apparent satiation for 198 d. In Experiment 2, fingerlings (mean weight: 47 g/fish) were stocked in 10 0.4-ha ponds at 24,710 fish/ha and were fed for 128 d. In both experiments, there were no significant differences in total feed fed, gross yield, final fish weight, survival, or Blood packed cell volume between fish fed diets with or without phytase. The diets also had no significant effects on pond water column total phosphorus or chlorophyll a concentrations, but soluble reactive phosphorus concentrations were significantly higher in ponds receiving the phytase diet in Experiment 2. Phytase superdosing of nutritionally complete feeds does not appear to have additional benefits beyond the standard phytase dose on production characteristics or packed cell volume of pond-raised hybrid catfish and had no beneficial effects on water quality.