Co-infection of Fusarium incarnatum FHHS2 and Acinetobacter bohemicus FHHK1 in captive-reared Hilsa shad, Tenualosa ilisha (Hamilton, 1822)

Tenualosa ilisha popularly known as ‘Hilsa’ is one of the most commercially important euryhaline food fish species in South Asian countries. Co-infection of Fusarium incarnatum FHHS2 and Acinetobacter bohemicus FHHK1 was reported for the first time in captive-reared pre-adult T. ilisha (average length 22.30 ± 0.92 cm and weight 93.48 ± 28.06 g) that had manifested skin lesions in freshwater pond during November–December 2022. The infected fish showed lethargy, abnormal swimming behaviour, blackening of gills, red streaks on the fins, erosions of the skin, and sloughing of the scales resulting in 40% mortality of the stock. Microscopic observation revealed the presence of aerial slightly curved conidia, septate macroconidia, and randomly spread microconidia. The fungal species was confirmed as F. incarnatum FHHS2 (NCBI GenBank accession number OR030402) by ITS sequencing. It clustered with known pathogenic F. incarnatum (NCBI Accession no. AY633745) counterpart associated with black gill disease of Penaeus monodon Fabricius (99.46% homology) in phylogenetic tree. We have also isolated, identified, and characterised A. bohemicus FHHK1 from the infected fish which clustered with A. bohemicus reported in the lakes of Indian subcontinent (100.00% homology). No parasite was found in different organs of the moribund hilsa shad. Significant histopathological alterations were observed in the skin, gill, and kidney of infected hilsa. Our study records the first report of F. incarnatum FHHS2 and A. bohemicus FHHK1borne infection in hilsa during its domestication in freshwater pond.