Efficacy of formalin treatment against saprolegniasis in a medium carp (Puntius gonionotus): an experimental evaluation under mid-hill conditions of Meghalaya

Abstract

Saprolegniasis in fish, caused by oomycete water molds of the genus Saprolegnia, poses a significant threat to aquaculture operations, particularly in cold-water environments that favour the proliferation of these opportunistic pathogens. This study evaluated the therapeutic efficacy of formalin bath treatments against Saprolegnia infections in Puntius gonionotus, an emerging aquaculture species, under the mid-hill conditions of Umiam, Meghalaya. Experimental infection was established by cohabiting partially infected fish with moribund conspecifics and inducing dermal abrasion to achieve uniform, full-body infection. Fully infected fish were then subjected to formalin immersion at 0 ppm (control), 50 ppm, 100 ppm, and 150 ppm for 30 or 60 seconds, administered on alternate days over five days to allow recovery between treatments and minimize chemical stress. Infection severity was scored on a standardised scale encompassing clinical signs, behavioural changes, integumentary lesions, ocular pathology, mucus depletion, and anorexia. Two-way analysis of variance revealed significant main effects of formalin dose and treatment duration, as well as their interaction, on infection intensity reduction. The highest dose of 150 ppm applied for 60 seconds produced the greatest reduction in infection severity (83.3%). These findings support formalin chemotherapy as an effective disease management intervention for hill aquaculture operations.