USE OF NONLINEAR-REGRESSION TO EVALUATE THE EFFECTS OF PHYTASE ENZYMETREATMENT OF PLANT PROTEIN DIETS FOR RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

The effects of dietary phytase enzyme treatment and increasing ration on growth, body composition, nutrient digestibility and retention and phosphorus release in effluent water were studied in rainbow trout (On corhynchus mykiss). Rainbow trout (initial weight: 115.3 +/- 0.49, mea n +/- S.D.) were randomly distributed among 24 tanks and fed two exper imental diets (A and B) each at six feeding levels (0.5, 1.0, 1.5, 2.0 , 2.5 b.w. and satiation for 49 days). The two diets contained 33% soy bean meal and differed only by the addition of 1000 U phytase/kg to di et B. The apparent digestibility coefficients for dry matter, crude pr otein, lipid, N-free extract, gross energy and ash of the two diets di d not differ statistically. The phytase in diet B increased apparent d igestibility of phosphorus (P) from 58.6 to 68.1% (P < 0.01). Daily ga in and FCR improved in fish fed diet B with feeding levels greater tha n 1.5 and the best fit of the data was by using logistic and quadratic regression, respectively. Body protein, ash and P content decreased i n fish fed diet A and with increasing ration up to 2.0% feeding rate a nd then reached a plateau. In contrast, body energy concentrations inc reased up to the same feed ration level and than levelled off. A signi ficant difference (P < 0.05) between diets was only observed for body ash content. Body protein, ash and P retention decreased while energy retention increased in fish fed diet A and with increasing feeding lev els. Best fit was obtained by using an exponential model for body prot ein (P < 0.05) and a quadratic model for the other body composition va riables. Phosphorus released into the environment was higher for fish fed diet A (P < 0.05) and increased with increasing feeding level. A s emilogarithmic model showed the best fit of the experimental data for P release. (C) 1998 Elsevier Science B.V.