Toxic Effects And Mechanism Of Enrofloxacin Pollution On Grass Carp In Water

Antibiotics are widely used in aquaculture.Since antibiotics cannot be completely digested and absorbed by the body after entering the body,most of them will be released into the environment in their original form or metabolite form.Enrofloxacin(Enrofloxacin,ENR),a quinolone antibacterial agent,is intended for livestock and aquatic products.ENR is often detected in aqueous environments,with concentrations usually ranging from ng/L to μg/L.ENR can negatively affect non-target organisms in the environment.However,previous studies on ENR focused on pharmacokinetics and residual status.The ecotoxicological studies of aquatic organisms are scarce.In this study,ENR was used as contaminant and grass carp(Ctenopharyngodon idella)was used as experimental animal.Physiological and biochemical,histomorphology,molecular techniques and sequencing techniques were used to investigate the effects of different concentrations of ENR on growth,intestinal flora and metabolism of grass carp.Integrated biomarker response(IBR)index was calculated to evaluate the toxicity of ENR to grass carp.The main results are as follows:(1)ENR exposure resulted in a significant increase of thyroid hormone(THs)in grass carp plasma after 21 days of exposure,which remained significant after 14 days of purification.In addition,it interferes with the expression of key genes in the growth hormone/insulin-like growth factor(GH/IGF)axis and hypothalamic-pituitary-thyroid(HPT)axis.The results showed that ENR exposure could affect the expression of key genes on the GH/IGF axis and HPT axis and interfere with the secretion levels of GH and THs.Thus,affecting the growth of fish.(2)ENR can induce hypoglycemia in grass carp by inhibiting gluconeogenesis and promoting glycolysis and aerobic metabolism.At the same time,ENR can reduce lipid utilization and catabolism of grass carp,causing liver function injury and metabolic disorders.In addition,it can also cause changes in the composition,structure and diversity of intestinal flora of grass carp,affecting the health of grass carp.Gut microbes can also influence the body by regulating metabolism-related indicators.After ENR exposure,the abundance of functional genes related to carbohydrate,amino acid,nucleotide and energy metabolism increased,which in turn helped grass carp adapt to ENR.(3)ENR exposure for 21 days can cause oxidative damage,neurotoxicity,and affect digestive enzyme activities of grass carp.According to the IBR radar map,catalase(CAT)and acetylcholinesterase(AChE)activities have a high response to ENR.The IBR index showed that 100μg/L ENR had a greater effect on grass carp.Histopathological results showed that ENR caused hepatocyte damage and induced apoptosis of grass carp hepatocytes.This study evaluated the toxicity effects of ENR on grass carp at individual,tissue and gene levels.It is hoped to provide some reference for the toxicity assessment of ENR in other aquatic animals.At the same time to assess the ecological risk caused by the abuse of antibiotics.In addition,it provides a scientific basis for guiding the rational application of ENR in aquaculture industry,so as to reduce the environmental problems caused by its excessive use.