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¹ Department of Aquaculture, Fisheries Faculty, İstanbul University, 34470 Istanbul, Turkey Viewed : 5427 - Downloaded : 5590 In vivo and in vitro protein digestibility of rainbow trout (Oncorhynchus mykiss) fed four different commercial feeds produced by means of extrusion or steam pressure methods was examined. At the end of the feeding trials, the live weight gain (LWG), feed conversion ratio (FCR), specific growth rate (SGR) and feed consumption (FC) were examined. According to the results at the end of the feeding trials, the difference between the feed consumption values was found significant (P≥0.05). The feed conversion ratio values were 1.1 in the groups fed extruded feed (A, B) and 1.3 - 1.6 in the groups fed with steam pressured (C, D) feed. The feed samples and the feces obtained from feeding tanks were analyzed in order to determine the proximate composition and also calculate in vitro protein digestibility. Relative protein digestibility for in vitro values was found by using porcine-tripsin enzyme. According to the results, the relation between in vivo and in vitro protein digestibility values was compared. In vivo digestibility ratios were found 94.9% and 89.1% in the fish fed extruded feed groups and 94.4% and 93.4% in the fish fed steam pressured feed groups. In vitro protein digestibility values were 66.7%, 63.6% in extruded feeds and 57.6%, 51.5% in steam pressured feeds, respectively.

As a result, protein digestibility and feed efficiency ratio values in the rainbow trout fed extruded feeds were found better than the steam pressured feeds in this study. Keywords : Rainbow trout (Oncorhynchus mykiss), protein digestibility, in vivo and in vitro digestibility method