RESEARCH ARTICLE Isolation and Characterization of Bacteria from the Intestine of Clarias batrachus for Probiotic Organism Arindam Ganguly 1 • Amrita Banerjee 1 • Asish Mandal 2 • Mohammad Ali Khan 3 • Pradeep Kumar Das Mohapatra 4 Received: 16 January 2017 / Revised: 18 September 2018 / Accepted: 29 November 2018 Ó Zoological Society, Kolkata, India 2018 Abstract Clarias batrachus (Linn.) in India is at a deteriorating state. The use of probiotic organism is one of the alternatives to promote fish nutrition in worldwide aquaculture. An extensive study was performed to isolate and identify probiotic bacteria from the gut of the C. batrachus. Quantitative and qualitative analysis of bacterial flora associated with the intestine of C. batrachus were carried out. Total viable bacterial count in the intestine of catfish was 1.61 9 10 10 cfu/g. Thirty-two different bacte- rial isolates were selected from the intestinal microflora of C. batrachus. Gram-positive rod-shaped bacteria domi- nated (81%) the populations in catfish. The five intestinal isolates (PKA1, PKA2, PKA17, PKA18 and PKA19) showed antagonistic properties against common fish pathogens - Vibrio harveyi, Vibrio vulnificus and Vibrio parahaemolyticus. The strain PKA17, PKA18 and PKA19 were identified as Lysinibacillus sphaericus, Bacillus cereus and Bacillus thuringiensis respectively by the 16S rDNA sequencing. Keywords Aquaculture Á Clarias batrachus Á Probiotic Á Antagonistic effect Introduction The Asian catfish, Clarias batrachus (L.) is widely rec- ognized for its nutritional and economic significance (Ganguly et al. 2017). The species is found in a variety of habitats including fresh and brackish water, low-land, streams, swampy or paddy fields and shows exceptionally well tolerance level at varied environment (Talwar and Jhingran 1991). It has good growth rate, efficient feed conversion ratio and sustainability in oxygen-depleted, hyper-ammonium, stressful water condition (Argungu et al. 2013). However, the species is presently at a deteriorating state in the Asian countries due to the exploitation of its natural habitats, intermittent periods of drought, reclamation of wetlands and uncontrolled introduction of exotic fishes. Another major cause of species deterioration is attributed by pathogenic infections (Ahmed et al. 2012). In recent decade, prevention and control of aquatic diseases have focused on the use of probiotics instead of chemothera- peutic agents and antibiotics as these agents may result in unfavorable alteration of the microbiota and involve in the emergence of antibiotic resistant bacteria (Aarestrup 1999; Nayak and Mukherjee 2011). Probiotics confer protection against pathogens by production of antimicrobial sub- stances and endorse fish nutrition by breakdown of indi- gestible components and production of vitamins & Pradeep Kumar Das Mohapatra pkdmvu@gmail.com Arindam Ganguly arindam_ganguly@yahoo.com Asish Mandal mandalasish71@gmail.com Mohammad Ali Khan mdmaths@gmail.co 1 Department of Microbiology, Vidyasagar University, Midnapore, West Bengal 721102, India 2 Department of Botany, Ramananda College, Bishnupur, Bankura, West Bengal 722122, India 3 Department of Mathematics, Ramananda College, Bishnupur, Bankura, West Bengal 722122, India 4 Department of Microbiology, Raiganj University, Raiganj, Uttar Dinajpur, West Bengal 733134, India 123 Proc Zool Soc https://doi.org/10.1007/s12595-018-0283-x T H E Z O O L O G I C A L S O C I E T Y K O L K A T A