Dietary microalgal mixture improve survival, growth performance, lipid metabolism, and inflammation in black seabream (Acanthopagrus schlegelii) fed high-fat diet

Metabolic disorders induced by high-fat diet (HFD) or other stimuli are the major challenges in aquaculture. The present study was devoted to systematically and comprehensively investigate the effects of dietary supplementation with marine microalgae (Phaeodactylum tricornutum:Tetraselmis sp.:Isochrysis galban = 6:3:1) on growth performance, feed intake, tissue morphology, biochemical indices of blood and organs, as well as multi-organ molecular indices of lipid metabolism and inflammation in black seabream (Acanthopagrus schlegelii) fed HFD. Fish with an average weight of 0.73 +/- 0.13 g were fed four isonitrogenous diets with varying lipid levels over a period of 62 days: normal fat diet (NFD, 11 % lipid), HFD (18 % lipid), HFD with 5 % microalgae (5MHFD) and HFD with 10 % microalgae (10MHFD). Compared to the HFD, both 5MHFD and 10MHFD significantly increased the survival rate from 63.49 % to 81.00 % and 91.00 %, respectively. The 10MHFD also demonstrated enhanced final weight, feed intake, weight gain rate, and specific growth rate, alongside reduced feed conversion ratio and hepatosomatic index. Moreover, the dietary microalgal mixture mitigated hepatic lipid deposition, with hepatic triglyceride content in microalgal groups being less than 40 % of that observed in the HFD. In the liver, 10MHFD significantly reduced the content of total cholesterol and low-density lipoprotein cholesterol as well as increased the activities of catalase, superoxide dismutase, and glutathione peroxidase compared to the HFD. Histological analysis revealed that the intestinal villi of fish fed microalgal mixture exhibited significantly greater height and density with more uniform and neat arrangement than those in fish fed HFD. Additionally, the dietary microalgal mixture mitigated the oxidative stress, decreased lipase activity, and increased protease activity. Furthermore, microalgal mixture inhibited the expression of lipogenesis gene (fatty acid synthase) and stimulate the expression of lipolysis-related genes (peroxisome proliferator-activated receptor alpha and carnitine palmitoyltransferase 1A). The marine microalgal mixture also increased the expression of anti-inflammatory cytokine interleukin-10 and decreased the expression of pro-inflammatory cytokine interleukin-1 beta in the liver, intestine, and kidney. In conclusion, dietary supplementation with the marine microalgal mixture improved lipid metabolism and attenuated lipid deposition in liver as well as alleviated inflammation and oxidative stress in both the liver and intestine. These effects promote overall health and enhance survival and growth performance in black seabream subjected to HFD.