Journal of Agricultural Science; Vol. 10, No. 11; 2018 ISSN 1916-9752 E-ISSN 1916-9760 Published by Canadian Center of Science and Education 101 The Effects of Kefir Usage for Probiotic Purpose on Growth Performance of Brook Trout (Salvelinus fontinalis) Huriye Ariman Karabulut 1 , Ilker Zeki Kurtoglu 1 & Ozay Kose 1 1 Department of Aquaculture, Faculty of Fisheries, Recep Tayyip Erdogan University, Rize, Turkey Correspondence: Huriye Ariman Karabulut, Department of Aquaculture, Faculty of Fisheries, Recep Tayyip Erdogan University, Rize, Turkey. Tel: 90-535- 619-2784. E-mail: huriye.ariman@erdogan.edu.tr Received: July 5, 2018 Accepted: September 2, 2018 Online Published: October 15, 2018 doi:10.5539/jas.v10n11p101 URL: https://doi.org/10.5539/jas.v10n11p101 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 W f (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. Keywords: Salvelinus fontinalis, kefir, growth, survival rate 1. Introduction As in aquaculture, the goal of all sectors of farming is yield. 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). Several studies used probiotics to increase growth performance and strengthen immune systems of farmed fish (Korkut et al., 2003). Probiotics are microorganisms that are known to be beneficial to living beings which compete with pathogenic bacteria in cultivation conditions and are not pathogenic or toxic (Yaman, 2000; Ozdemir & Kelestemur, 2009). According to the Turkish Food Codex Communique on Fermented Milk Products, kefir is a milk product that is a dairy product that fermentes lactose in fermentation (Kluyveromces morxianus) and has yeast cells (Saccharomyces unisporus, Saccharomyces cerevisiae and Saccharomycess exiguus) that do not ferment lactose. However, 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, active kefir grains added to milk, is a dairy product formed as a result of lactic acid and ethyl alcohol fermentations (Guzel Seydim et al., 2000). 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). Kefir grains are yellowish white in color, irregularly shaped, similar to cauliflower, 3-20 mm in diameter. When kefir grains are added into the milk (25 C and 22 hours) they ferment the milk and reveal the kefir product. Kefir grains can be removed by filtration through the kefir product and used again in the next process. As the process repeats over time, kefir grains grow volumetrically and multiply (Guzel-Seydim et al., 2000).