Marker residue depletion from the skin-on fillet tissue of rainbow trout exposed to AQUI S 20E:

Among the data required by the U.S. Food and Drug Administration (FDA) for approval of an aquaculture drug are the data that characterize the depletion of a drugs marker residue from the edible fillet tissue of fish after exposure. Eugenol is the marker residue for AQUI-S 20E, a product proposed for use as a sedative for fish.Rainbow trout (Onchorynchus mykiss; a representative cold water fish species) was exposed to AQUI-S 20E in water at a temperature of 9 C, a temperature that is representative of the lower range of temperatures where rainbow trout would be sedated. Eighty fish were exposed to a nominal AQUI-S 20E concentration of 100 mg/L for 60 min. Groups of 16 fish were sampled immediately after 60 min of exposure (the 0 min sample group), then at 15, 30, 90, and 150 min after the fish were transferred to fresh, flowing water. Skin-on fillets from each fish were analyzed for eugenol concentrations by using a FDA approved method for determining eugenol concentrations in fish fillet tissue. The method involved extracting eugenol from the tissue with acetonitrile, recovering eugenol from the tissue extract by using solid phase extraction techniques, and determining eugenol concentrations in the final extract by using high pressure liquid chromatography with absorbance detection techniques.Results indicated that maximum eugenol concentrations in the fillet tissue were measured immediately after the exposure (mean, 47.5 g/g). Eugenol concentrations decreased to 1.9 g/g by 150 min after the fish were transferred to fresh, flowing water. The depletion of eugenol from the fillet tissue was rapid (t1/2 = 31.7 min).