LAUSR

Abstract 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.