Potential for dietary phytase to improve the nutritive value of canola protein concentrate and decrease phosphorus output in rainbow trout (Oncorhynchus mykiss) held in 11 degrees C fresh water

This study assessed the potential for using dietary phytase to improve the nutritive value of canola protein concentrate (CPC) for rainbow trout, and to concomitantly minimize phosphorus discharge into the environment. Eight diets were prepared. LT-anchovy meal (AM) provided 89% of the protein in th e basal diet, whereas in the remaining diets, 59% of the protein originated from CPC by replacement of AM protein. Four CPC diets were supplemented wi th phytase (Natuphos(R)) at levels of either 0, 500, 1500 or 4500 phytase u nits (FTU)/kg diet together with 4505 mg/kg phosphorus. Two CPC diets conta ined 1500 FTU/kg and either 0 or 2253 mg/kg of supplemental phosphorus. The seventh CPC diet contained no phytase or supplemental phosphorus. A commer cial trout feed served as an industry control. All diets were fed to tripli cate groups of rainbow trout (initial weight, 17.9 g) to satiation daily fo r 84 days. Mean water temperature was 11.0 degrees C. The level of phytic a cid degradation and the apparent availability of dietary phosphorus were as certained for all groups. Fish fed the CPC diets, regardless of their phyta se and phosphorus levels, exhibited growth rates, feed efficiencies and pro tein utilization comparable to those of control fish. There was, however, a clear positive dose-response of phytase on dietary phytate digestibility a nd phosphorus availability was improved significantly by the highest level of phytase. We conclude that dietary phytase has potential to improve the n utritive quality of CPC for rainbow trout and the availability of phytate p hosphorus. (C) 1999 Elsevier Science B.V. All rights reserved.