Impact of acute fonofos exposure on skeletal muscle of zebrafish: Histopathological and biometric analyses

It is widely known that pesticides generally do not show target specificity, and off-target species are strikingly affected by these chemicals. In the current work, histological changes in skeletal muscles of zebrafish (Danio rerio) caused by fonofos, an acetylcholinesterase (AChE) inhibitor organophosphate insecticide, were examined. Zebrafish were treated with 1 mg/L, 2 mg/L and 4 mg/L of fonofos for 96 hours. Skeletal muscle samples were removed from the pectoral region and embedded in paraffin. Sections were stained with Mayer's Hematoxylin and Eosin, Gomori's Trichrome and Periodic Acid Schiff techniques. Histopathological alterations were investigated by light microscopy. Fibrosis, intramyofibrillar vacuoles, disintegrated myofibrils, splitting of myofibers, atrophic and disappeared fibers, histoarchitectural loss, necrosis and progressive decrement in glycogen content were noted. Muscle fiber diameter measurements were also performed. Statistical analysis showed that measured fiber diameters of all fonofos exposed groups were significantly different from the control group, and they decreased in a concentration-dependent manner. These results suggested that fonofos caused significant myoarchitectural impairments in non-target freshwater zebrafish.