Pond-raised hybrid catfish, male Ictalurus punctatus X female Ictalurus furcatus, do not respond to microbial phytase “super-dosing”

Authors: LI, MENGHE - Mississippi State University; WISE, DAVID - Mississippi State University; MISCHKE, CHARLES - Mississippi State University; AARATTUTHODIYIL, SUJA - Mississippi State University; TIWARI, AMBIKA - Mississippi State University; LUCAS, PENELOPE - Mississippi State University; Tucker, Craig; Torrans, Eugene; Perera, Thishya

Submitted to: Journal of the World Aquaculture Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2018
Publication Date: 2/1/2019
Citation: Li, M.H., Wise, D.J., Mischke, C.C., Aarattuthodiyil, S., Tiwari, A., Lucas, P.M., Tucker, C.S., Torrans, E.L., Perera, T.D. 2019. Pond-raised hybrid catfish, male Ictalurus punctatus X female Ictalurus furcatus, do not respond to microbial phytase “super-dosing”. Journal of the World Aquaculture Society. 50:78-86.

Interpretive Summary: Phytase is an enzyme that is often added to animal feeds to improve the availability of the essential mineral nutrient, phosphorus, from plant-based feedstuffs. Past research has shown that phytase added to catfish feeds at relatively low doses (250-500 phytase units/kg of feed) improves fish growth over plant-based diets without inorganic phosphorus supplements and can completely replace dicalcium phosphate supplementation in feeds for pond-raised channel catfish. Recently there has been interest in “super-dosing” with higher levels of phytase (2500-5000 phytase units/kg feed) to more quickly and completely break down organic phosphates in p[lant feedstuffs and increase the availability of nutrients needed for growth and normal physiological functions. Scientists with Mississippi State University and the USDA-ARS Warmwater Aquaculture Research Unit conducted two pond studies in consecutive years to evaluate responses of hybrid catfish to phytase “super-dosing” of existing commercial catfish feeds. Phytase super-dosing did not have additional benefits beyond the standard phytase dose on growth, survival, feed conversion, or blood hematocrit, and also had no beneficial effects on water quality. The standard phytase dose of 500 phytase units/kg of feed remains the recommendation for feeds used for final grow-out of pond-raised hybrid catfish.

Technical Abstract: Two experiments were conducted in consecutive years to evaluate responses of hybrid catfish, male Ictalurus punctatus X female Ictalurus furcatus, to “super-dosing” of 6-phytase added to existing commercial catfish feeds. In each experiment, two diets with or without a phytase super-dose (2,500 and 5,000 phytase units [FTU]/kg, respectively) were compared. In Experiment 1, fingerlings (mean weight: 59 g/fish) were stocked into 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 into 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 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 super-dosing 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.