| Summary: | Antibiotic growth promoters have been banned in animal husbandry and aquaculture in China, since 2020. Florfenicol (FLO) is the most used antibiotics in aquaculture for controlling various bacterial disease in fish, although its effect on health of farmed fish remains a concern. In the present study, European seabass (Dicentrarchus labrax) reared under flow-through aquaculture system (FAS) and recirculating aquaculture system (RAS), were fed on diets supplemented with FLO for 10 d, followed by a 20-d withdrawal period. The effects of FLO on the growth performance, intestinal digestive enzyme activities, serum biochemical parameters, antioxidant enzymes, and expression of related genes, were evaluated. The results showed that FLO exposure inhibited growth performance of D. labrax although this was recovered after stopping the feeding. Besides, FLO suppressed α-Amylase and trypsin activities in the intestine, and the amounts of nutrition-related indicators were also affected. In addition, FLO exposure upregulated liver cellular damage markers (ALT, ALP, and AST) during the treatment phase, although it did not pose a high potential for liver damage. We also observed elevated levels of SOD, CAT, and MDA in gills, indicative of oxidative stress on the cultured fish. Moreover, integrated biomarker response results indicated that fish in RAS had higher growth performance and immunity in the late post-treatment phase, relative to those in RAS, after FLO exposure. This was attributed to high-efficient water treatment of RAS. Overall, these results indicate that exposure to FLO modulates digestive enzyme activities and antioxidant response in European seabass, thereby affecting their growth performance and immune response under different aquaculture modes.
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