PRELIMINARY-STUDY ON THE KINETICS OF OXYTETRACYCLINE IN SHELLFISH EXPOSED TO AN EFFLUENT OF A LAND-BASED FISH FARM - EXPERIMENTAL APPROACH

In many ancient saltmarshes marine fish farms are now being developed. These farms, during their production cycles, use many chemical and ve terinary products to prevent or fight disease. Since effluents from th e farms ave discharged directly into shellfish rearing areas, it is ne cessary to be aware of how shellfish accumulate such substances. An ex perimental apparatus allowed the creation of a fish farm effluent cont aining oxytetracycline (OTC) for a seven day treatment period This eff luent was poured into three test tanks, into which individuals of thre e edible species of bivalves, Crassostrea gigas, Ruditapes philippinar um and Scrobicularia plana, hack previously been placed. The highest c oncentrations were observed in C. gigas (average 1.42 mu g.g(-1) wet w eight). After treatment, the OTC concentration decrease was gradual an d slow in C. gigas, reaching 0.68 mu g.g(-1) wet weight 14 d after the end of medication. Concentrations were stable in R. philippinarum and S. plana until the end of the experiment. Differences observed in the kinetics and maximal OTC concentration values may be related to the f iltering rate of the species and their feeding behaviour. These findin gs illustrated the long persistence of OTC in shellfish. This may be r elated to the availability of OTC from sediment, the formation of comp lexes between OTC and some mineral or organic components of the bivalv es, and their low xenobiotic metabolism. Considering the dilution proc esses of the coastal ecosystem, one might surmise that the influence o f such contamination is only restricted to the vicinity of the farms. Nevertheless, special care should be taken in the utilization of such substances, especially in integrated aquaculture systems.