Effects of dietary oxidized fish oil on growth performance, antioxidant defense system, apoptosis and mitochondrial function of juvenile largemouth bass (Micropterus salmoides)

Four isonitrogenous and isolipidic diets containing fresh fish oil (peroxide value, POV: 7.2 meq kg(-1), diet FR) and three degrees of 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, body composition, antioxidant defense system and mitochondrial function of juvenile largemouth bass, Micropterus salmoides. After a 12-week feeding trial, fish fed the OX155 obtained significantly higher (P < .05) weight gain, final body weight and specific growth rate than the FR because of their remarkable higher feed intake. Malonaldehyde (MDA) levels were markedly increased in plasma, liver and mitochondria of largemouth bass fed diet OX564 than those fed FR. Fish fed the OX564 also obtained the highest levels of lipid peroxidation (LPO) than other groups. Antioxidant enzyme activities and mRNA levels were stimulated after 12 weeks of feeding. The highest activities of superoxide dismutase (SOD) and glutathione peroxidase (Gpx) in liver and plasma were obtained in group OX564. The relative expression of TNF-alpha was decreased with the increasing oxidative degree of dietary fish oil, while the relative expression of Caspase 8, 9 and 10 were increased with the increasing oxidative degree of dietary fish oil. The relative expression of Bcl-2 and Bcl-xL were lower in fish fed the OX275 and OX564. The lowest activities of malate dehydrogenase (MDH), succinate dehydrogenase (SDH) and citrate synthase in liver were found in group OX564, in which the ATP level also lower than other groups. Liver mitochondria of fish fed the FR were more resistant to the calcium-induced mitochondrial swelling. More reactive oxygen species (ROS) were produced in fish fed the OX564 compared with those fed the FR after the 12-week trial. Membrane potential and Ca2+ induced swelling of mitochondria also affected by dietary oxidized fish oil. The present study indicated that dietary oxidized fish oil increased oxidative stress, influenced antioxidant system and induced apoptosis of largemouth bass, hepatic mitochondrial function and energy metabolism also were impaired by dietary oxidized fish oil.