Abstract
The effects of probiotically used kefir on growth, survival rate and meat yield characteristics of brook trout (Salvelinus fontinalis) were investigated in this study. For this purpose, kefir was added to trial diets at different rates 20 ml/kg feed (G2), 40 ml/kg feed (G3) while commercial fish feed was used as a control 0 ml/kg feed (G1). Total 270 fish with mean weight 24.38±0.37 g were used during the experiment. Each group had three replicate, and 30 fish were placed in each tank. Experiment was carried on for 90 days. At the end of the experiment, some growth parameters, survival rate and meat yields of the groups were determined. 
 
 The best weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR) and survival rate (SR) values were obtained in G2 (20 ml/kg) group (104.31±0.11, 1.30±0.08, 1.40±0.18, 98.88±0.51 respectively). At the end of the study, the differences between the control group and the other groups were not statistically significant in terms of FCR, Condition factor (CF) and survival rate (P < 0.05). However, the differences between the control group and the other groups were statistically significant in terms of WG, WGR and Wf (P < 0.05). The statistical difference between the G2 group and the G1 group was not significant at the SGR, whereas the statistical difference between the G2 group and the G3 group was significant (P < 0.05).
 
 The body composition of the fish, hepatosomatic index (HSI), viscerosomatic index (VSI) values, fish meat crude protein and crude fat content were not affected by the addition of kefir to fish diet at different ratios. As a result, it was observed that the addition of kefir at 20% of the diet positively affected the growth performance and survival rate of the brook trout.
Highlights
As in aquaculture, the goal of all sectors of farming is yield
This study investigated the effects of adding kefir into feed of trout in different ratios on live weight gain, specific growth rate, condition factor, feed conversion ratio, survival rate and flesh yield characteristics in brook trout (S. fontinalis)
Live weight gain, specific growth rates, Feed conversion ratio (FCR) values and temperature changes were determined for each period
Summary
The idea behind using feed additives to increase yield is to affect the metabolism of the animal and increase its rate of utilizing the feed. This way, it is possible to achieve healthy development and higher yield with less feed (Karabulut, 2008). In the fermentation process, Kefir grains are used which have different strains of Lactobacillus kefir, Leuconostoc, Lactococcus and Acetobacter genus in particular (Anonymous, 2009). Kefir, which is similar in contents to yogurt, contains various beneficial bacteria and yeasts, especially species of Lactobacillus (Rea et al, 1996; Jianzhong et al, 2009)
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