Effects of environmental antibiotics on growth， intestinal health， and muscle quality of Ctenopharyngodon idella

Objective This study aimed to investigate effects of environmental oxytetracycline （OTC）， norfloxacin （NOR）， and sulfamethoxazole （SMX） on the growth， intestinal health and muscle quality of Ctenopharyngodon idella， thereby providing insights for antibiotic toxicological assessment.Method A control group （0 ng/L） and three antibiotic threatment groups SMX （1000 ng/L）， NOR （1000 ng/L） and OTC （5000 ng/L）， were set up. Ctenopharyngodon idella with an average body mass of 50.52±0.70 g were reared for 90 d to determine their growth performance， intestinal and muscle microstructures， biochemical indexes of the intestinal tract， muscle， and serum， as well as indexes related to muscle quality.Result Exposure to environmental OTC significantly increased the feed coefficient and intestinal amylase activity （P<0.05，the same below）， and triggered the stress response of Ctenopharyngodon idella， but such exposure had no significant effect on the growth performance of Ctenopharyngodon idella. Histological and biochemical analyses of Ctenopharyngodon idella intestinal tract revealed that exposure to environmental antibiotic increased the contents of protein carbonyl， reactive oxygen （ROS）， and malondialdehyde （MDA） of Ctenopharyngodon idella intestinal tissues， decreased the contents of total antioxidant capacity （T-AOC） and glutathione （GSH）， and reduced the activity of super-oxide dismutase （SOD）， indicating that the exposure to environmental antibiotic caused the intestinal antioxidant responses in Ctenopharyngodon idella. Exposure to environmental antibiotic increased the contents of interleukin-8 （IL-8）， interleukin-1β （IL-1β）， tumour necrosis factor-α （TNF-α）， and transforming growth factor-β （TGF-β） in the intestinal tissues of Ctenopharyngodon idella. In addition， contents of Occludin， Claudin-1， Claudin-2 in the SMX group and the Claudin-1 content in the OTC group were significantly lower than those in the control group， indicating that exposure to environmental antibiotic caused intestinal inflammatory response and disrupted the intestinal barrier of Ctenopharyngodon idella. Meanwhile， the observation of intestinal microstructure of Ctenopharyngodon idella exposed to environmental OTC and SMX revealed structural damage to the intestinal tract. In addition， the exposure to environmental OTC significantly reduced the water holding capacity， recovery， and elasticity of muscle； however， such exposure did not affect the muscle fibre growth of Ctenopharyngodon idella.Conclusion Exposure to environmental antibiotics disrupts the intestinal health of Ctenopharyngodon idella， but does not affect its normal growth； exposure to environmental OTC reduces the muscle quality of Ctenopharyngodon idella to a certain extent.