Ethanol Extracts of Yacon and Ginger in Diet of Juvenile Olive Flounder (Paralichthys olivaceus): Effect on Growth, Feed Utilization, Body Composition, Plasma Chemistry and Challenge Test against Vibrio anguillarum

Development of natural immunostimulants as dietary additive keeps receiving scientist's interest and administration of ethanol extract of additive is one of the effective methods to concentrate their bioactive compounds to improve their effects. Dietary inclusion effect of ethanol extracts of yacon and ginger on growth, feed utilization, body composition, plasma chemistry of fish and challenge test against Vibrio anguillarum compared to a commercial probiotic (Super lacto (R)) was determined. Three hundred and sixty juvenile fish were distributed into 12, 50 L flowthrough tanks. Four experimental diets were prepared. Additive-free basal diet was served as the control (CON) diet. The 1% ethanol extracts of yacon and ginger, and 0.5% Super lacto (R) were included into the CON diet, referred to as the YCE, GGE and SUP diets, respectively. Each diet was hand-fed to triplicate groups of fish for 8 weeks. After the 8-week feeding trial, fish were injected with V. anguillarum and survival was monitored for the next 7 days. Dietary additives did not affect weight gain, feed utilization, whole body composition and plasma parameters of fish. Survival of fish fed the YCE and GGE diets was significantly higher than that of the fish fed the CON and SUP diets at the end of the 7-day post observation. Ethanol extracts of yacon and ginger can be effectively used as natural immunostimulants for olive flounder at occurrence of V. anguillarum.