Effects of different dietary vegetable oils on growth and intestinal performance, lipid metabolism and flesh quality in gilthead sea bream

Abstract

This study tests the effects of feeding different vegetable oils (VO) in gilthead sea bream with the aim of improving sustainable aquafeeds. Juveniles were fed ad libitum with ten isonitrogenous (46%) and isolipidic (22%) diets with a 75% fish oil (FO) replacement, differing in VO composition leading to two experimental blocks: fish fed with VO blends or mono-substituted diets. Growth parameters, skin and muscle colour, muscle texture, plasma metabolites, digestive capacities, and transcript levels of intestinal lipid transport, muscle dynamics and lipid metabolism-related genes in white muscle and adipose tissue were studied. In fish fed high-palm oil diets, final body weight and mesenteric fat significantly increased, while effects were not found in hepatosomatic index, reflecting tissue-specific lipid accumulation. Relative intestinal length increased significantly with dietary soya oil (SO) content, suggesting a compensatory mechanism to improve nutrient absorption capacity. Plasma parameters showed few changes upon dietary treatments. Lipase activity was unaltered, while intestinal fatp1b expression increased in animals fed blended diets high in rapeseed oil (RO). In adipose tissue, expression of nuclear receptors pparβ and lxr was modified by dietary fatty acids (FA) profile; however, regarding lipid metabolism and β-oxidation genes, only lpl showed significant differences, suggesting that FA uptake and oxidation, but not de novo lipogenesis is what appears to determine the increase in adipose tissue mass. In fish fed blended VO diets, lpl expression showed a positive correlation with MUFA dietary content, suggesting that some FA present in RO enhance its expression, according to data from fish fed mono-substituted diets. In muscle, fish fed blended VO diets also showed a positive correlation of lpl expression with dietary MUFA, whereas in mono-substituted, it was significantly higher in fish fed SO, suggesting other mechanisms are involved in LPL regulation. Concerning β-oxidation genes in muscle, significant differences were detected in cpt1a expression for fish fed blended VO diets, whereas hadh and cpt1b were unaltered, suggesting slight FA uptake regulation in mitochondria. Expression levels of genes related to myogenic processes were not greatly modified by dietary lipid sources except for myogenin in blended VO diets-fed fish, showing a similar profile as that in body weight and opposite with the differentiation marker mhc. This study provides new information regarding the effects of dietary VO, demonstrating moderate effects in lipid homeostasis without adverse effects on growth performance, leading to a transversal view of the responses and interactions from intestine to muscle growth and flesh quality.