In vivo and in vitro digestibility of diets and feedstuffs for rainbow trout (Oncorhynchus mykiss)

Summary Knowledge of feedstuff and diet digestibility is a basic requirement for the elaboration of well-balanced diets and for the evaluation of diet quality. The aim of this work was to compare the apparent protein digestibility coefficients of animal and plant protein feedstuffs and Compounded diets determined by an in vitro method with the values obtained in vivo with rainbow trout (Oncorhynchus mykiss), using the Institute Nacionale de la Recherche Agronomique (INRA) apparatus for fish faeces collection. The in vitro protein digestibility was determined according to the technique described by the Association of Official Analytical Chemists (AOAC), using pepsin (obtained from porcine stomach niucosa, Sigma-P-7000) to digest the samples. Overall results showed that differences in the digestion coefficients obtained with the two methods were statistically significant (P < 0.01). These differences were also significant within each group of feeds tested separately (feedstuffs and compounded diets). The overall correlation coefficient between the in vivo and in vitro digestibility was also very low. The correlation coefficient between in vitro and in vivo digestibility of feedstuffs was considerably higher than that for compounded diets, although not statistically significant (P < 0.05). It is concluded that the in vitro digestibility method used in this study is not a good enough criterion for the estimation of the apparent digestibility of protein by rainbow trout.