Abstract
The influence of the oral administration of oxytetracycline (OTC) and immune-enhancing agents such as lactoferrin (LF), fucoidan (Fu) and γ-oryzanol (γ-OR) on the intestinal flora of Japanese flounder, Paralichthys olivaceus, were examined. Slight changes in the intestinal flora of fish with the oral administration of OTC were observed. However, it was found in this group that the ratio of OTC resistant bacteria to total intestinal bacteria was elevated significantly. In the intestine of LF-, Fu- and γ-OR-treated fish, both decreases in Streptococcus sp. and Enterobacteriaceae and an increase in Vibrio sp. were shown. In the fish administered Vibrio anguillarum (afamous pathogenic bacterium for fish) with and without LF, LF suppressed the number of Enterobacteriaceae and V. anguillarum in fish intestine. It also gave fish on extended survival time and restrained the amount of bacteria in hepatopancreas and spleen tissues in V. anguillarum-treated fish. The results suggest that the utilization of immuno-enhancing agents such as LF, Fu and γ-OR is better compared to that of antibiotics such as OTC for the prevention and the treatment of infectious diseases in hatchery fish.
