en aquaculture aquaculture پژوهشي Orginal research papers This study was carried out to determine effects of diets supplemented with two bacterial strains <em>(Lactococcus lactis </em>and<em> Weissella confusa)</em> on the growth performance, immune indices and intestinal microflora of great sturgeon juveniles. At the beginning of the feeding trial, the mean weight (&plusmn;SD) of the fish was 79.44<span dir="RTL">&plusmn;</span>3.18 g. At random, 15 fish were stocked per each fiberglass tank (1m&times;1m&times;0.5m) containing 300 L freshwater. The diets were prepared through spraying 50 ml bacterial suspensions containing 150, 300, and 450 mg of the bacterial strains per kg of pelleted diets to make certain concentrations 1.5&times;10⁹cfu/g (T₁), 3&times;10⁹cfu/g (T₂), 4.5&times;10⁹cfu/g (T₃). The blood neutrophils in the T₁ and T₂ significantly increased as compared to the control group and T₃. Lymphocytes in the control and T₃ were significantly more than T₁ and T₂. However, eosinophils showed no change between the fish fed with the supplemented diets and control group. Monocytes in T₃ considerably decreased when compared to T₁, T₂, and control. IgM and C₃in the experimental treatments were significantly higher than the control. Lysozyme, C₄, and ACH50 in T₁ an T₂ were significantly higher than T₃ and control. Colony count of lactic acid bacteria in the intestine of fish in T₁ and T₂was significantly higher than the control and T₃groups. Colony count of the aerobic and facultative anaerobic bacteria in the intestine of fish in the medium of TSA in control was significantly more than T₁ and T₂. Since the TSA medium is a kind of non-selective environment and provides sufficient nutrients for a wide range of microorganisms, the medium indicated that intestinal microflora condition was worse in the control fish. The growth performance indices (weight gain, biomass increase, specific growth rate, daily weight gain, and condition factor) demonstrated no significant difference between treatments and control. There was no significant difference in term of FCR between control, T₁, and T₃. Overall, it can be stated that the two bacterial strains could induce favorable influence on intestinal microflora, immune indices, biochemical parameters, and growth performance at two levels of 150 mg (T₁) and 300 mg (T₂) especially in the T₂. Huso huso, Probiotic, Growth performance, Intestinal microflora, Immune indices 1206 1217 http://jifro.ir/browse.php?a_code=A-10-2629-3&slc_lang=en&sid=1 R. Ghorbani Vaghei ghorbani_v2@yahoo.com 100319475328460041086 100319475328460041086 Yes International Sturgeon Research Institute A.R. Shenavar Masoule shenavar1969@gmail.com 100319475328460041087 100319475328460041087 No International Sturgeon Research Institute R. Kazemi Rezkazemi2000@yahoo.com 100319475328460041088 100319475328460041088 No International Sturgeon Research Institute J. Jalilpour jalilpoorj@gmail.com 100319475328460041089 100319475328460041089 No International Sturgeon Research Institute A. Hoseinpour ahpour.Z@gmail.com 100319475328460041090 100319475328460041090 No International Sturgeon Research Institute M.H. Sayed Hassani mirhamedhassani@Yahoo.com 100319475328460041091 100319475328460041091 No International Sturgeon Research Institute M. Alizadeh Rudposhti ANA_Alizadeh2003@Yahoo.com 100319475328460041092 100319475328460041092 No International Sturgeon Research Institute