Dietary inclusion effect of various sources of phyto‐additives on growth, feed utilization, body composition, and plasma chemistry of olive flounder (Paralichthys olivaceus), and challenge test against Edwardsiella tarda compared to a commercial probiotic (super lacto®)

Abstract

AbstractInclusion of various sources of additives in aquafeeds is practically helpful to elevate the growth performance and disease resistance of aquatic animals. An 8‐week feeding trial was conducted to determine the inclusion effects of phyto‐additives (yacon, ginger, and blueberry) into diets on olive flounder growth, feed utilization, chemical composition, and plasma chemistry, and to challenge test against Edwardsiella tarda in comparison to a commercial probiotic SUP (Super lacto®). Six hundred juvenile olive flounder were randomly allocated into 15, 50 L flow‐through tanks (40 fish per tank). Five experimental diets were formulated. No additive was included in the control (Con) diet. One percent of yacon, ginger, and blueberry powders, and 0.5% Super Lacto® were included at the expense of wheat flour and water in the Con diet, also referred to as the YCP (yacon powder), GGP (ginger powder), BBP (blueberry powder), and SUP diets, respectively. All experimental diets were hand‐fed to triplicate groups of fish twice a day until they were visually satiated for a period of 8 weeks. Following the 4‐ and 8‐week feeding trials, 10 and 20 fish were taken from each tank and artificially infected with E. tarda, and then survival was monitored for the next 6 and 8 days after infection, respectively. At the end of the 8‐week feeding trial, no significant difference was observed in weight gain, feed consumption, feed utilization, chemical composition, and plasma chemistry in olive flounder. However, the survival of olive flounder fed the GGP diet was significantly (p < 0.004 and p < 0.02, respectively) higher than that of fish fed the SUP, BBP, and Con diets, and the SUP and Con diets after the 4‐ and 8‐week feeding trials, respectively, according to the Kaplan–Meier survival curve. In conclusion, phyto‐additive, especially GG, can be used as an effective immunostimulant in the olive flounder diet at the occurrence of E. tarda.