Lipid metabolism and plasma metabolomics of juvenile largemouth bass Micropterus salmoides were affected by dietary oxidized fish oil

During the storage, fish oil is susceptible to peroxidation to form toxic lipid derivatives, dietary intake of oxidized fish oil would induce oxidative stress and inflammation in animals, but it was not clear about the relation between oxidized fish oil intake, lipid metabolism and oxidative stress. Four isonitrogenous and isolipidic diets containing fresh fish oil (peroxide value, POV: 7.2 meq kg(-1) , diet FR) and oxidized fish oil (POV: 155, 275 and 564 meq kg(-1) , diet OX155, OX275 and OX564, respectively) were formulated to investigate the effects of dietary oxidized fish oil on growth performance, plasma metabolomics and lipid metabolism of juvenile largemouth bass, Micropterus salmoides. After the 12-week feeding trial, fish fed the OX155 obtained significantly higher (P < .05) weight gain than fish fed FR because of their higher feed intake. Malonaldehyde (MDA) levels were increased in plasma and liver of largemouth bass fed OX564 diet than those fed FR. Untargeted metabolomics ultra-performance liquid chromatography coupled with quadrupole time of flight mass spectrometry (UPLC-QTOF-MS) was performed to invest the differences of plasma metabolites in fish fed different oxidative degrees of fish oil. Lipid metabolism, especially phospholipids and sterol metabolism in largemouth bass were significantly affected by oxidized fish oil. Dietary oxidized fish oil decreased membrane phospholipids unsaturated degree and increased plasma lysophospholipid contents in largemouth bass. Several bile acids were decreased, while many cholesterols and vitamin D3 related metabolites were increased with the increasing oxidative degree of fish oil. Lipoprotein transport related genes and lipid oxidation related genes mRNA levels were increased in fish fed highly oxidized fish oil. Cholesterol synthesis related gene 7-dehydrocholesterol reductase (DHCR7) mRNA level was increased with the increasing oxidative degree of fish oil. Bile acid metabolism related gene 12a-hydroxylase (CYP8B1) was higher in fish fed OX275 diet. The increased vitamin D3 related metabolites in fish fed oxidized oil may associate with the decreased mRNA levels of RXRa and 24 - hydroxylase (CYP24A1). In conclusion, dietary oxidized fish oil may affect the health of fish through decrease the unsaturated degree of phospholipids and fatty acids, increase the contents of oxidized cholesterol and lysophospholipid in plasma, and repress the bile acid synthesis.