Effect of protease and phytase supplementation on growth performance and nutrient digestibility of rainbow trout (Oncorhynchus mykiss, Walbaum) fed soybean meal-based diets

An experiment was conducted to evaluate effects on growth, body composition and nutrient digestibility of addition protease and phytase to soybean meal-based diet in rainbow trout. Seven soybean meal-based diets were prepared by adding protease, phytase and mixture of both enzymes at two different levels (1 and 2 g kg−1) to a base diet without enzymes. Mixed enzymes (1, 2 g kg−1) were prepared by adding protease and phytase at the same doses (0.5 + 0.5 and 1 + 1 g kg−1). Diets consisted of 31% fish meal and 44% dehulled hexane extracted soybean meal. At the start of the experiment, 45 rainbow trout (initial mean body weight 88 g) were stocked into each of 21 fibre tanks. After 90 days, there were no significant differences on the growth, feed conversion ratio, digestibility of protein and lipid among the groups. Results of this study showed that the addition of protease or phytase as mix to soybean meal-based diet could not increase growth and nutrient digestibility in trout