The influence of probiotic (isolated based on phytase activity) on growth performance, body composition, and digestibility of rainbow trout, Oncorhynchus mykiss

In this study, the effect of using bacteria with phytase activity (AM) isolated from traditional dairy products was investigated for use in feeding rainbow trout. For this purpose, 450 rainbow trout with an average initial weight of 6.50 +/- 0.43 g were randomly distributed to treatments in a controlled feeding experiment lasting 8 weeks. Experimental diets consisted of treatments with two levels of 20% and 40% soybean meal, each with two levels of AM and the commercial phytase (SP) of 1000 FTU/kg (AMT20, AMT40, SPT20, and SPT40), 2000 (AMS20, AMS40, SPS20, and SPS40), and zero (C20 and C40) as the control treatment. The results showed that the body weight gain, daily growth rate, and nutrient digestibility were higher in C20 treatment than C40 (p < 0.05). The use of SP and AM had a significant effect on body composition in fish fed diets containing 20% and 40% soy (p < 0.05). In the treatment with 40% soybean replacement level, bacteria with phytase activity could significantly increase the protein content (p < 0.05). The addition of bacteria to the AMS40 treatment neutralized the negative effect of 40% soy replacement on growth, protein, fat, and calcium and magnesium digestibility (p < 0.05). The present study showed that using AM (especially at the dose of 2000 FTU/kg) could increase the replacement level of soybean for fishmeal in rainbow trout diet not only without a negative effect on growth, but also for improvement of fish performance.