Effects of enrofloxacin and povidone-iodine on immunity, intestinal microbes, and transcription pathways of grass carp

Abstract

Abstract The gut microbiota is crucial for maintaining the internal ecological balance of fish health. In aquaculture, antibiotics and disinfectants are frequently used to manipulate the host gut microbiota, but the combined effects on asymptomatic fish remain unclear. We investigated the effects of single and combined treatments with antibiotics and disinfectants on grass carp gut health, immune response, microbiome dynamics and transcriptome profile. In a two-week trial, grass carp were exposed to enrofloxacin (10 mg/kg) in the basal diet or povidone-iodine (0.05 mg/L) in freshwater. Enrofloxacin and povidone iodine induced oxidative stress, reduced the activity of digestive enzymes and altered the diversity of the gut microbiota. Transcriptome analysis showed downregulation of immune-related signaling pathways. Both treatments decreased mRNA expression of immune-related genes and induced histopathologic changes and apoptosis. In conclusion, enrofloxacin and povidone-iodine can induce oxidative stress, disrupt the balance of the gut microbiota, decrease mucosal immune responses and induce apoptosis in grass carp.