Changes in the fecal microflora of goldfish Carassius auratus with the oral administration of oxytetracycline

The present study was performed to investigate the effect of oxytetracycline (OTC) on the intestinal microflora of goldfish Carassius auratus. OTC was orally administrated at 50mg/kg body weight, and fecal flora of three goldfish was successively determined. As a result, two fish harboured Aeromonas hydrophila and Bacteroides type A as predominant organisms during the experimental period, whereas Bacteroides type A was not detected in another fish during the ad-ministration of OTC though Aeromonas hydrophila was the dominant one. The reason being suggested was that either the day-to-day variation of intestinal microflora or the different response of each microflora to OTC. In addition, it was generally observed in all the goldfish that the OTC resistant bacteria became dominant 1-6 days after oral administration of the drug.