EFFICACY OF DICALCIUM AND DEFLUORINATED ROCK PHOSPHATES AS DIETARY PHOSPHORUS SOURCES FOR CHANNEL CATFISH (ICTALURUS-PUNCTATUS)

Two experiments were conducted to evaluate the efficacy of dicalcium p hosphate (DCP) and defluorinated phosphates (DFP) as dietary phosphate sources for channel catfish, and to test the effect of their solubili ty in neutral ammonium citrate (NAG) on phosphorus utilization. The fo llowing phosphates were tested: DCP with a NAC solubility of 90.7%, DF P with a high NAC solubility (HDFP, 85.4%), a DFP with a medium NAC so lubility (MDFP, 62.7%), and a DFP with a low NAC solubility (LDFP, 44. 6%). In Experiment 1, 12 purified diets (32% protein and 2.9 kcal dige stible energy g(-1)) containing either DCP, HDFP, or MDFP and four lev els of total phosphorus 0.2, 0.3, 0.4, or 0.8% were tested. In Experim ent 2, four purified diets containing either DCP, HDFP, MDFP, or LDFP at 0.49 total phosphorus (0.40% available phosphorus based on DCP) wer e tested. Juvenile channel catfish (4.8 g fish(-1) and 3.8 g fish(-1) for Experiments 1 and 2, respectively) were raised under laboratory co nditions and fed twice daily to approximate satiation for 12 weeks. In Experiment 1, weight gain and feed consumption increased and feed con version ratio (FCR) decreased linearly as dietary phosphorus concentra tion increased regardless of phosphate type. Fish fed diets containing HDFP consumed significantly more feed, had a lower FCR, and gained mo re weight than fish fed diets containing DCP and MDFP regardless of di etary phosphorus concentration. Bone ash and phosphorus concentrations showed a similar pattern as weight gain in regard to response to diet ary phosphorus concentration. As dietary phosphorus concentration incr eased, bone ash and phosphorus concentration increased linearly regard less of phosphate type. Fish fed diets containing HDFP had higher bone ash and phosphorus concentration than those fed diets containing DCP and MDFP regardless of dietary phosphorus concentration. In Experiment 2, fish fed the HDFP diet consumed significantly more feed than other groups of fish and gained significantly more weight than fish fed die ts containing DCP and MDFP, but not more than fish fed the diet contai ning LDFP. Feed conversions were the same for all fish regardless of t reatment. There were no significant differences in bane ash and bone p hosphorus concentrations among the treatments. These data indicate tha t DCP and DFP are equally efficacious for use as phosphorus sources fo r channel catfish. The data do not support the contention that a highe r NAC solubility correlates to a higher utilization of phosphorus for channel catfish.