Effect of dietary inclusion of the ethanol extracts of yacon and ginger on growth, feed utilization, plasma chemistry and body composition of juvenile olive flounder (Paralichthys olivaceus) and challenge test against Vibrio anguillarum compared to a commercial probiotic (Super lacto®)

Abstract

The effect of dietary inclusion of the ethanol extracts of yacon (YC) and ginger (GG) on growth, feed utilization, body composition, plasma chemistry of juvenile olive flounder and challenge test against Vibrio anguillarum compared to a commercial probiotic (Super lacto®) was determined. Three hundred and sixty juvenile fish were randomly distributed into 12, 50 L flow-through tanks (30 fish per tank). Four experimental diets were prepared in triplicates. The control diet (CON) contained no additive. The 0.5% Super lacto® and 1% ethanol extracts of YC and GG were included into the CON diet, referred to as the SUP, YCE and GGE diets, respectively. Each diet was hand-fed to satiation twice daily for 8 weeks. After the 8-week feeding trial, fish were artificially infected with V. anguillarum and mortality was monitored for the next 7 days after infection. Dietary additives did not affect the weight gain, specific growth rate, feed efficiency, whole body composition and plasma chemistry of fish. However, protein efficiency ratio was significantly higher in fish fed the CON and GGE diets than that of fish fed the SUP and YCE diets. The cumulative mortality of fish fed the YCE and GGE diets was significantly lower than that of fish fed the CON and SUP diets at 72 h after infection until the end of the 7-day post observation. Therefore, the ethanol extracts of YC and GG can be effectively utilized to stimulate the immunity of olive flounder to lower mortality at occurrence V. anguillarum.