Study on florfenicol-contained feeds delivery in Dicentrarchus labrax seawater recirculating and flowing aquaculture systems

Abstract

Florfenicol (FLO) is the most commonly used antibiotic in aquaculture for various fish bacterial disease treatments. To ensure that low amounts of residue occur in cultured aquatic products, it is important to study the depletion of antibiotics in the process of aquaculture. Recirculating aquaculture system (RAS) is a promising aquaculture model with high water utilization that could effectively reduce nutrient concentrations; however, the fate of antibiotics under recirculating conditions is still unclear. In the present study, European seabass (Dicentrarchus labrax) were fed with FLO-medicated feeds at 10 mg/kg body weight/d for 10 d and the FLO depletion from water and tissues in RAS and flowing aquaculture system (FAS) cultures for 20 d were evaluated. The FLO residues in the RAS and FAS outlet peaked at 3 h and decreased to levels comparable to the pretreatment level at 12 h. With prolonged feeding, FLO was prone to accumulate in the RAS and peaked at 2.06 μg/L at 10 d of treatment, which was significantly higher than that in the FAS. To further compare the contributions among the water treatment units in the RAS, protein skimmer showed the most effective depletion of FLO, and then UV disinfection device and biofilter. Moreover, FLO showed the highest bioconcentration factors (BCF) values in the gill and the BCFs in muscle and liver from fish in the RAS were higher than that in the FAS. The present study reports the FLO depletions in a saltwater RAS for the first time and evaluates the contributions of different treatment units of the RAS on FLO depletion. The results showed the preliminary distribution of FLO in the RAS, which is valuable information for applying antibiotics in aquaculture and the designing water treatment units for RASs.