The influence of dietary oxolinic acid on fluidised bed biofilter performance in a recirculation system for rainbow trout (Oncorhynchus mykiss)

The effect of medicated feed, containing 2.35 +/- 0.01 mg oxolinic acid (OA ) g(-1), upon the performance of fluidised bed (FB) biofilters was examined over a 29-day period. Rainbow trout were used as stock animals in duplicat e recirculation systems. OA was detectable within the systems throughout th e period of study, with bulk water OA concentrations reaching 1.24 mg l(-1) at their highest point. Sludge levels of OA were measured at 60 mg day(-1) at peak. A mass balance for OA was undertaken on day 21 of the study. Seve nty-two percent of the antibiotic could be recovered from the trout, sludge and water, with fish being of minimal significance at trial termination. T he treated feed did not effect biofilter performance, either during the fee ding period (7 days duration) or for 14 days post-feeding, with respect to nitrification rates. In separate studies, which employed a scale model of t he recirculation system, maximum nitrification rates (MNR) were examined us ing media from each of the biofilters and four doses of OA (0.1-100 mg l(-1 )). OA did not effect MNR, but water turbidity and bacterial count increase d. (C) 2000 Elsevier Science B.V. All rights reserved.