The effect of fipronil exposure on the activity of biotransformation enzymes and histology in the liver of grass carp

Abstract

Fipronil (FPN) is an insecticide used in agriculture. This study focused on the biotransformation process and the histopathological effects of FPN in the liver of grass carp. Fish were exposed to environmental concentrations of FPN (3, 6, and 10 ug l-1) for up to 14 d. The alterations in phase I and II biotransformation enzyme activity (ethoxyresorufin-O-deethylase [EROD] and glutathione-S-transferase [GST]), malondialdehyde (MDA) content, and histopathology in the liver were studied on the 1st, 3rd, 7th, and 14th days. Results showed that EROD (dose-dependent) and GST activity (time-dependent) increased. The MDA content increased in a time- and dose-dependent manner. The most common types of hepatological damage were steatosis, vein dilatation, pyknosis, and increased melanomacrophage centers, probably due to oxidative stress originating from biotransformation enzyme activity (R2 = 0.88 for GST and MDA). The degree of tissue change (DTC) at the highest dose indicated moderate damage to the liver (R2 = 0.82 for GST and DTC). Nevertheless, the level of EROD and GST activity and MDA content indicated complex interactions among various phase I and phase II biotransformation enzymes which should be investigated in future studies with more replications.