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a b s t r a c tThis study aimed to evaluate the effects of adding guar gum, a non-starch polysaccharide, to the diet of Mugil liza juveniles. The juveniles (mean weight = 0.38 ± 0.01 g) were fed one of three diets with increasing supplement levels (4%, 8%, and 12%) and a control diet without additional gum for 60 days, in order to evaluate the effects on zootechnical performance, proximate composition, liver parameters, morphological alterations to the intestinal tract, and modulation of gastrointestinal microbiota. The animals fed 8% and 12% gum presented a significantly lower mean final weight, weight gain, specific growth rate, food intake rate, and protein intake rate than the control. Adding gum to the diets also reduced the dry matter, crude protein, and carcass fat levels. All treatments with added gum resulted in increased liver glycogen, and the cholesterol levels were significantly reduced in fish fed 4% and 8% supplement levels. No intestinal morphological alterations were observed in the animals. However, a modulating effect was noted on the microbial community, altering the bacterial quantity and composition throughout the tract segments. The use of guar gum is not recommended in Mugil liza diets, at least above 4%.

Summary The effects of increasing levels of dietary dextrin on growth performance, body composition, blood chemistry and hepatic triglycerides and glycogen levels were evaluated for juvenile Lebranche mullet, Mugil liza Valenciennes 1836, Mugilidae). Five diets were formulated to be isonitrogenous (350 g kg−1) and isolipidic (6 g kg−1) with increasing dextrin levels (D150: 150 g kg−1; D200: 200 g kg−1; D250: 250 g kg−1; D300: 300 g kg−1; D350: 350 g kg−1). The experimental diets were offered to the fish for 34 days, four times per day, until apparent satiation. Each treatment was tested in triplicate, with nine fish per tank (mean weight 4.69 ± 0.31 g). Fish were reared in a recirculating aquatic system of 15 fibreglass tanks each containing 50 L of saltwater. Growth parameters and body composition of the mullets were not significantly affected (P > 0.05) by the dietary treatments. Plasma glucose concentration declined (P < 0.05) when dietary dextrin increased from D250 to D300, but recovered to the previous values (in reference to D150 and D200) when fish were fed with D350. Glycated haemoglobin, plasma proteins, triglycerides and cholesterol showed no significant differences among these treatments. Hepatic glycogen reached a maximum in treatment D250, followed by D350, D200 and D300, with the lowest concentration of liver glycogen found in D150 (P < 0.05). The concentration of liver triglycerides showed an increase (P < 0.05) in treatments D300 and D350 compared with D200. In conclusion, Mugil liza juveniles can be fed diets with high levels of dietary dextrin with no deleterious effects to their growth or plasma biochemistry, hepatic glycogen or triglycerides.

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