Impacts of dietary konjac glucomannan supplementation on growth, antioxidant capacity, hepatic lipid metabolism and inflammatory response in golden pompano (Trachinotus ovatus) fed a high fat diet

Abstract

This study examined the effect of konjac glucomannan (KGM) supplementation in diets with different lipid levels on growth, antioxidant capacity, hepatic lipid metabolism and inflammatory response in juvenile pompano (Trachinotus ovatus). Triplicate groups of fish (12.07 ± 0.21 g) were fed eight experimental diets containing two lipid levels of 9% (basal-fat diet, BFD) and 18% (high-fat diet, HFD), and four levels of KGM (0, 0.5, 1 and 2%) for 60 days. Pompano fed HFD exhibited markedly lower growth and feed efficiency than fish fed BFD, and KGM supplementation, particularly at 1% inclusion, significantly improved growth performance and feed efficiency in fish fed both BFD and HFD. In addition, Pompano fed HFD showed higher whole-body lipid and lower protein contents than fish fed BFD. Irrespective of dietary lipid level, whole body, dorsal and ventral muscle were reduced by dietary KGM supplementation up to 1% while the opposite was found for whole body protein content. Dietary KGM also significantly reduced the HSI, liver lipid contents, as well as lipid droplets in the liver. Supplementation of KGM to both BFD and HFD significantly reduced serum total cholesterol, triglyceride, low-density lipoprotein cholesterol and free fatty acids levels. Furthermore, irrespective of dietary lipid level, increasing dietary KGM supplementation enhanced serum IgM level, lysozyme and alkaline phosphatase activities, and reduced serum alanine aminotransferase and aspartate aminotransferase activities. Dietary KGM also increased liver total antioxidant capacity, superoxide dismutase and catalase activities, and decreased malondialdehyde concentration in fish fed both HFD and BFD. Dietary KGM significantly increased serum glutathione peroxidase, superoxide dismutase and catalase activities and reduced malondialdehyde concentrations in fish fed BFD, and enhanced serum total antioxidant capacity and glutathione peroxidase activity in fish fed HFD. Supplementation of KGM increased the expression of genes associated with lipid catabolism (pparα, cpt1, hsl) and lipid transport (fabp1, apoB100 and cd36), and decreased the expression of lipid anabolism related genes (srebp1, pparγ, fas and acc). Moreover, the expression of pro-inflammatory cytokines including tumor necrosis factor α and interleukin-8 were down-regulated, while expression of the anti-inflammatory cytokine transforming growth factor β1 was increased by KGM supplementation. In conclusion, supplementation of KGM at 1% of diet improved growth, feed efficiency, antioxidant capacity, hepatic lipid metabolism and inflammatory responses in juvenile pompano, and can mitigate excessive deposition of lipid in tissues of farmed fish.