Abstract

Azoxystrobin, a strobilurin fungicide widely used in agriculture, is increasingly detected in freshwater ecosystems, raising concerns about its potential impact on non-target aquatic species such as grass carp (Ctenopharyngodon idella). This study focused exclusively on the histopathological alterations induced by azoxystrobin (25% SC; a commercial suspension concentrate formulation) in the gills, liver, kidney, and intestine of C. idella under acute (1.6 ppm, 24 h) and short-term sublethal (0.16 ppm, 4–8 days) exposure conditions. Exposure produced clear concentration and time-dependent changes, including epithelial lifting and lamellar fusion in the gills, hepatocellular vacuolation and necrosis in the liver, tubular degeneration in the kidney, and villus atrophy and mucosal ulceration in the intestine. Lesion severity increased with exposure duration and concentration, indicating organ-specific structural impairments. The histopathological alterations observed in this study complement previously reported biochemical and behavioral disturbances caused by azoxystrobin exposure in freshwater fish. The use of a water-dispersible commercial formulation eliminated the need for solvent or positive controls, thereby reducing animal use while maintaining experimental validity. Overall, the findings provide the first detailed multiorgan histopathological characterization of azoxystrobin toxicity in grass carp and highlight histopathology as a sensitive endpoint for evaluating pesticide effects in aquaculture-linked freshwater environments.

Key words: strobilurin fungicide; grass carp; gill lesions; liver pathology; aquatic ecotoxicology; freshwater fish.