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Not AvailableThe present study was undertaken to evaluate the effect of a probiotic strain, Bacillus circulans (BC) and prebiotics fructooligosaccharide (FOS) supplementation in Labeo rohita fingerlings subjected to sub-lethal nitrite stress. Earlier a sixty days feeding trial was conducted using eight experimental diets viz. T1 (106 cfu/g BC+0%FOS), T2 (108 cfu/g BC+0% FOS), T3 (0BC+1%FOS), T4 (0BC+2%FOS), , T5 (106 cfu/g BC + 1% FOS), T6 (106 cfu/g BC+2% FOS), T7 (108 cfu/g BC+1%FOS), T8 (108 cfu/g BC+2%FOS) & control (0BC+0%FOS) assigned to triplicate groups. After the initial experiment, fishes were subjected to sub-lethal nitrite (1/5 96 h LC50 = 2.08 mg/L) for another 30 days. At the end of the experiment growth and feed utilization parameters viz. weight gain, specific growth rate (SGR), feed conversion ratio (FCR) & survival percentage were calculated. Haemato-immunological parameters viz. total leukocyte count (TLC), total erythrocyte count (TEC), hemoglobin (Hb), hematocrit (Hct) values, lysozyme and respiratory burst activity were assayed after exposure to stress. Growth and feed utilization was significantly (p < 0.05) better in probiotic fed groups at all level of supplementation whereas prebiotics supplementation at 2% level had negative impact. Percentage survival was also better in the supplemented groups with highest survival observed in T4 group. Similarly, post challenge haemato-immunological parameters were better in supplemented group compared to control and higher levels were observed in combination groups (T4 and T5). From the present investigation, it can be concluded that probiotic B. circulans and prebiotics FOS supplementation improves immune status and thereby conferring better protection of L. rohita under sub-lethal nitrite stress.Not Availabl