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¹ The Key Laboratory of Aquaculture Nutrition and Feeds (Ministry of Agriculture and Rural Affairs), the Key Laboratory of Mariculture (Ministry of Education), College of Fisheries, Ocean University of China, Qingdao, 266100, China
² Department of Fisheries, Faculty of Natural Resources, Gonbad Kavous University, Gonbad, 163, Iran DOI : 10.4194/AQUAST961 Viewed : 1322 - Downloaded : 1143 This study aimed to evaluate the effects of Bifidobacterium animalis and Bifidobacterium lactis on growth, length-weight relationship and some biological indices of rainbow trout, Oncorhynchus mykiss fry. An iso-nitrogenous (50% crude protein) diet was supplemented with three different concentrations of a mixture of equal quantities of the two strains of Bifidobacterium, namely T1 (1×10⁷CFU/g), T2 (2×10⁷CFU/g), T3 (3×10⁷CFU/g) and a control (without bacteria). A total of 480 trout fries with an initial mean body weight of 0.53±0.19 g were randomly divided into four groups, each with 4 replicates. The fries were distributed into 16 fiberglass tanks (20 L total capacity) each filled with 15 L of water (water exchange rate of 2 L min^-1 and permanent aeration) at a density of 2 fries per liter. During the 8-week feeding trial, the mean water temperature was 17.66±1.33°C and that of pH was 7.63±0.08. All fish groups demonstrated positive allometric growth. Trout fries fed with diet T1 recorded significantly higher (P<0.05) gonadosomatic index, specific growth rate and mean weight gain. The highest final mean length (14.12±4.57 cm) was recorded in fry fed with diet T2. The lowest concentration of Bifidobacterium, T1 induced the best growth and it enhanced the biological indices of O. mykiss. Keywords : Bifidobacterium Gonadosomatic index Growth Length-weight Probiotic