DOES ORAL-ADMINISTRATION OF OXOLINIC ACID OR OXYTETRACYCLINE AFFECT FEED-INTAKE OF RAINBOW-TROUT

Short-term oral drug intake was measured in rainbow trout (Oncorhynchus mykiss) using radioactively labelled diets. In Experiment 1, duplicate groups of trout were fed either a control diet without antibiotic addition, or diets containing either 10g oxolinic acid (OA) or 10g oxytetracycline (OTC) per kg. In Experiment 2, triplicate groups of trout were fed diets containing either 1 or 10 g OA per kg. The trout, weighing 200-900 g, were kept in freshwater at 10-degrees-C. The fish were accustomed to feeding to satiation every 20 min, 20 h/day; the drugs were fed over a 6-h period. The amount of radioactive feed ingested by the fish was measured directly on anaesthetized fish with a portable gamma scintillation counter. The results showed that OA in the diet tended to reduce mean feed intake (mean reduction 17%) compared to controls. This reduction was, however, not significant (P = 0.09). Addition of OTC led to a 61% reduction in feed intake (P < 0.05).