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Aquaculture of tilapia is a new research venture in India. With intensification in farming practices, tilapia are increasingly susceptible to bacterial infections. This article describes the isolation and identification of pathogenic bacteria from cultured monosex Nile tilapia, Oreochromis niloticus (L.), that experienced moderate to severe mortalities in West Bengal, India between September and August 2014 and histopathological alterations in various organs. Gram-positive diplococci, identified as Streptococcus agalactiae with Streptococcus identification kits and 16S rDNA sequencing analysis, were isolated from the brain, operculum, and kidney. Other bacteria from the kidney were identified as Aeromonas sobria, A. caviae, Klebsiella pneumoniae ssp. pneumoniae, Escherichia coli, and Enterobacter cloacae. Staphylococcus epidermis was isolated from opercular hemorrhages. Histological sections of the infected tilapia brain revealed meningoencephalitis and granulomatous lesions. Sections from other organs indicated congestion, hemorrhagic and hyperplastic cells, necrosis, vacuolation, hemosiderin deposition, hypertrophic nuclei, melanomacrophage aggregation, and ruptured veins. This report is the first description of S. agalactiae as a primary pathogen causing meningoencephalitis in cultured tilapia in India. CORRESPONDING AUTHOR: H. Adikesavalu, S. Banerjee, A. Patra, T.J. Abraham [+] Department of Aquatic Animal Health, Faculty of Fishery Sciences, West Bengal University of Animal and Fishery Sciences, Chakgaria, Kolkata- 700094, West Bengal, India e-mail: abrahamtj1@gmail.com

The present study reports the first isolation of Chryseobacterium sp. and co-infection with Aeromonas hydrophila in pacu, Piaractus brachypomus fries cultured in West Bengal, India. The infected pacu fries showed white patches on gill, tail rot, skin discoloration, scale loss, skin peeling, emaciation, and kidney inflammation. The yellow pigmented colony from the kidney of pacu on selective cytophaga agar was identified as Chryseobacterium sp. based on colony pigmentation, cell morphology, phenotypic characterization, and 16S rDNA gene sequencing. Phylogenetically, the members of the genus Chryseobacterium clustered together as a separate clade and the strain PLI2 (NCBI accession number KP898212) branched with a non-type strain C. indologenes VIT-CMJ1 (accession number KJ437473 ) with high node value (100). Yet, the strain PLI2 was distinctly different from closely related type strain C. indologenes LMG 8337 (accession number LN681561) with 97% DNA homology and low (80) node value or other type strains of NCBI GenBank database. The challenge experiments indicated that Chryseobacterium sp. PLI2 can cause substantial mortalities (25%) in abraded and bath (2.2 × 107/mL) treated pacu fries. The kidney of challenged pacu became pale and inflamed. Most likely, this report is a new record on the isolation of Chryseobacterium sp. from the kidney of P. brachypomus. Statement of relevance • Co-infection of Chryseobacterium sp. and A. hydrophila in Piaractus brachypomus caused nephropathy and large scale mortalities. • The record of a new bacterial disease Chryseobacterium sp. infection in Indian aquaculture is a serious cause for concern.

“Gill rot” caused by the Gram negative, long, rod shaped bacterium Flavobacterium sp. in a sewage fed farm growing Indian major carps in West Bengal, India, is described. The phenotypic and molecular characteristics, virulence and pathology of Flavobacterium sp. strain KG3 are also documented. The infected catla Catla catla had cutaneous haemorrhages, white patches on body and gill, gill rot and excess mucus secretion. On selective cytophaga agar, the isolate produced non-rhizoid yellow pigmented colonies. Phylogenetically, the strain KG3 was distinctly different from the closely related type strains of Flavobacterium species, though it branched with type strain F. hydatis DSM 2063 (NCBI accession number AM230487 ) with low node value. Histologically, the naturally infected catla gills showed cartilaginous tissue inflammation, mucus secretion, necrosis of gill filament with associated reduction in the number of lamellae per filament, obliteration of interlamellar water channels, and fusion of lamellae. Catla catla fingerlings experienced about 57% moralities within 5 days of abrasion and immersion in a bath containing 4.7 × 106 Flavobacterium sp. cells/mL. The abraded and unchallenged fingerlings recorded 20% mortality in 3 days. These results demonstrated the virulence of Flavobacterium sp. in catla especially during the winter season, which warrants its management measures. Statement of relevance Flavobacterium spp. are emerging as major pathogens of Indian freshwater fish. They can cause chronic mortalities in fish at low water temperature. Correct diagnosis and understanding the pathology would help manage flavobacterial infection in fish.

Indian catfish production is increasing over the years so as the frequency of diseases. In this report, the isolation of Stenotrophomonas maltophilia from the kidney of Clarias gariepinus juvenile with distended abdomen along with its phenotypic, molecular and phylogenetic characteristics was described. The diseased catfish juveniles in an earthen pond (1500 m 3 ) with high stocking density (≈ 60 nos/m 3 ) had body discoloration, fin/tail rot, focal cutaneous hemorrhage, distended abdomen, inflammation of internal organs and visceral hemorrhage. The abdominal cavity was filled with transparent jelly-like mass. The bacterial strain isolated from the kidney of catfish formed a monophyletic group with other strains of S. maltophilia based on genotypic characters and phylogenetic analyses. The strain S. maltophilia SK1 (NCBI accession number KP898215) was alpha-hemolytic, protease and lipase positive and weakly pathogenic to C. gariepinus juveniles. It caused only 35 ± 5% mortality at a level of 1.40 × 10 7 cells/fish via intraperitonial injection. While the intramuscular injection caused only 10% mortality. The dead fish up on challenge had distended abdomen with jelly-like mass. Understanding the pathology and pathogenesis of this emerging pathogen in cultured catfish would help manage the disease. Statement of relevance 1 Stenotrophomonas maltophilia is considered as an opportunistic pathogen of human and fish. 2 This species is emerging as a pathogen in cultured catfish Clarias gariepinus (Burchell, 1822). 3 Understanding the pathology and pathogenesis of this species would help manage the disease.

A new bacterial disease (flectobacillosis) caused by Gram negative, long rod shaped Flectobacillus roseus in captive held carp, rohu (Labeo rohita) in West Bengal, India is described. Besides the phenotypic and molecular characterization, histopathology of F. roseus of naturally infected and challenged rohu were studied. The affected rohu had loss of mucus and scale, discoloured body, peeled skin and rotten tail, but no signs of gill damage. On selective cytophaga agar, F. roseus produced pink to rose pigmented colonies. Phylogenetically, F. roseus RF1 formed a monophyletic branch with F. roseusEU921645 (96% sequence similarity) and Flectobacillus sp. KC588923 (94% sequence similarity). It caused significant mortalities in rohu when challenged. The naturally infected rohu showed epithelial disruption, inflammation and necrosis of skeletal muscle tissue accompanied by haemocyte infiltration. The kidney of challenged rohu showed proximal and distal tubule degeneration, necrosis, thickening of epithelial layer of proximal and distal tubules, necrotised haematopoietic tissue, nephritic tubule with widened lumen, vacuolation of tubular epithelium, glomerular congestion, desquamation, glomerulopathy with dilated Bowman's space, cellular and nuclear hyperprophy, pycnotic nuclei, melano-macrophage aggregates and granuloma-like inflammatory response. These results suggest that F. roseus can produce systemic pathology in kidney similar to many other known fish pathogens.

This study describes rapid detection of Flavobacterium columnare induced columnaris disease in cultured freshwater fish, viz., Labeo rohita, Ctenopharyngodon idella, Puntius sp. and Anabas testudineus by species-specific polymerase chain reaction. Gill discolouration, yellow necrotic areas, white patches on gill, saddle back and erosion of scales were the prominent clinical signs in all diseased fish, except Puntius sp., which had typical signs of ulcer at the base of dorsal fin. Of the nine disease cases, eight were found columnaris positive through culture independent species-specific PCR. The two sets of F. columnare specific primers such as ColF, ColR and Col72F, Col1260R yielded amplicons of around 675 bp and 1000 bp, respectively in all positive samples. Phylogenetically, the nucleotide sequences of the positive samples namely, C1 and RG1 formed monophyletic group with F. columnare, thus confirmed the infection as columnaris.