Effect of Dietary Supplementation of Glycyrrhetinic Acid and Tea Polyphenols on Depuration of 2-methylisoborneol from Blunt Snout Bream, Megalobrama amblycephala

Abstract_Off-flavor is a serious issue in cultured fish. It affects marketability and texture of fish and causes great economic losses in the aquaculture industry. Holding fish in a clean-water environment for some time is an effective method to depurate them although it involves weight loss. This study investigates the potential effects of dietary supplementation of glycyrrhetinic acid (GA) and tea polyphenols (TP) on the depuration of the strong odors of 2- methylisoborneol (MIB) from blunt snout bream, Megalobrama amblycephala. 560 fish, initial average weight of 48.75±0.48 g were distributed into 28 tanks at a rate of 20 fish per tank. Three diets, namely the control diet, a GA supplemented diet (0.3 g/kg), and a (TP) supplemented diet (0.3 g/kg) were used in this study. The control diet was randomly assigned to 20 tanks, 4 tanks with clean water (control), or with water containing 1μg/L MIB. During the first 28-day the fish in each treatment were hand-fed to apparent satiation three times daily. In the second phase (29-42 day), the control, GA, and TP treatments were divided into four groups: MIB, low density (LD), high density (HD), and dynamic sampling (DS) with twenty fish in DS, and fifteen fish in the others. Fish in LD, HD, and DS in all treatments were starved in clean water. Fish in the DS treatment were sampled at 0, 24, 48, 72 hours, at 7 and 14 days. No differences were observed in body weights between groups within the 28-day feeding trial (P>0.05). Fish in GA, LD, and HD groups had significantly lower hepatosomatic index (HSI) and intraperitoneal fat ratios (IPF) than the control, MIB, and TP groups (P<0.05). After 28 and 42 days, fish in the MIB group had higher MIB concentrations than the other groups (P<0.05). Scores of sensory characteristics were similar, with no statistical differences between the control, GA, and TP groups (P>0.05). MIB content decreased significantly in relation to longer depuration times (P<0.05). Fish weight in LD and HD treatments declined by 10% and 12% respectively after 14-day fasting. In conclusion, clean water depuration for fourteen days is an effective method to purge off-flavored flesh although it involves weight loss and dietary supplementation of GA and TP which also depurate MIB from flesh of Megalobrama amblycephala.