Abiotic stressors influence saprolegniasis infection, causing mass mortality in Pangasianodon hypophthalmus and Labeo rohita under cage culture in Eastern India.

Saprolegniasis is one of the most devastating fish diseases that cause fish mortality in aquaculture in winter season, leading to economic loss to the farmers. The mycotic infection in fish occurred during the winter season in inland open water bodies due to adverse environmental factors, poor culture practices, high stocking densities, rough handling, and physiological changes associated with immune suppression. In the present investigation, we studied the environmental factors for disease progress in Pangasianodon hypophthalmus and Labeo rohita, characterization of oomycetes, and screening of potential antifungal agents against fish pathogenic oomycetes. Mortality and infection patterns have a relationship with water temperature in the present investigation. We noted that co-habitat infection was found in L. rohita and caused mortality. The presence of certain abiotic factors and susceptible host species led to the outbreak of disease in cage culture. The morphological and molecular identification of the etiological agent was carried out, and the PCR amplicon sequence of the ITS gene fragment showed similarities with Saprolegnia aenigmatica. The optimum temperature required by S. aenigmatica was between 20 and 25 °C for hyphae growth. In vitro assessment revealed that fluconazole (FLZ), boric acid (BA), and potassium permanganate (KMnO4) were unable to control zoospore colonization at higher concentrations. Clotrimazole and hydrogen peroxide inhibited colonization in 10 ppm and 100 ppm, respectively. The present investigation identified and confirmed the causative agent of saprolegniasis outbreak with associated environmental factors and approached to develop antifungal therapeutics to combat infection in the inland open-water bodies.