Temperature affects the metabolism of fish, and fish of different sizes have different tolerances to temperature. The aim of this experiment was to compare two sizes of juvenile spotted seabass, Lateolabrax maculatus (with average weights of 57.91 ± 11.57 g and 13.92 ± 2.77 g, respectively) for changes in physiological, biochemical, and molecular mechanisms under acute heat stress. Experimental fish were exposed to acute temperature increasing from 23 °C to 32 °C, and the mortality rate was noted at various heat stress exposures (0, 3, 6, 12, 24, 48, and 72 h). Moreover, serum and liver were obtained before and after heat stress. The activities of aspartate aminotransferase (AST), alanine aminotransferase (ALT), superoxide dismutase (SOD), malondialdehyde (MDA), lactic acid (LD), lactate dehydrogenase (LDH), glucose, and hepatic glycogen, and the expression of heat shock proteins (HSP70, HSP90) and apoptosis-related genes (BAX, caspase-3) in two sizes of spotted seabass were measured. Results showed that the contents of AST, ALT, SOD, MDA, LD, and glucose as well as the expression level of BAX and mortality were higher in large spotted seabass than in small spotted seabass within 12 h. These results indicate that the large spotted seabass had higher levels of oxidative stress and more severe liver damage, resulting in a higher mortality. Furthermore, the HSPs expression level of small spotted seabass was higher and the mortality was lower than that of large spotted seabass. Therefore, we considered that the large spotted seabass has lower levels of HSPs expression, causing their physiological response to be elevated to resist heat stress. In conclusion, spotted seabass with larger size has a poorer tolerance to heat stress compared with spotted seabass with smaller size. The smaller fish size was possibly resistant to heat stress by regulating the HSPs expression level in a more active extent.

The study investigated the impact of chlorogenic acid (CGA) supplementation in a high-fat diet (HFD) on growth, lipid metabolism, intestinal and hepatic histology, as well as gut microbiota in spotted sea bass. A total of 540 fish were fed six experimental diets, including a normal fat diet (NFD), a high-fat diet (HFD), and HFD supplemented with 100, 200, 300, and 400 mg/kg CGA (named HFD1, HFD2, HFD3, and HFD4, respectively) for 7 weeks. The results showed that HFD feeding increased growth and hepatic lipid deposition compared to that in the NFD group. Inclusion of 300 mg/kg CGA in HFD decreased the HFD-induced hyperlipemia (p < 0.05). Additionally, compared to the HFD group, the HFD4 group showed significant reductions in serum aspartate transaminase (AST) and alanine transaminase (ALT) levels as well as hepatic malondialdehyde (MDA) content, while also improving liver total antioxidant capacity (T-AOC) (p < 0.05). In the CGA-containing groups, hepatocytes were arranged more neatly than those in the HFD group, and there was a reduction in lipid deposition and hemolysis in the liver. Supplementation of CGA had effects on intestinal structure including an increase in mucosal thickness, as well as villus number and width. The diversity of intestinal flora in the CGA-containing groups was higher than those in the HFD group, and supplementation of 200 mg/kg CGA significantly increased the abundance of intestinal bacteria (p < 0.05). HFD4 feeding increased the intestinal Bacteroidetes to Firmicutes ratio and decreased the abundance of Vibrio. The highest value abundance of Actinobacteriota was found in the HFD2 group. Overall, HFD caused negative effects, and supplementation of 200–400 mg/kg CGA to HFD improved fat deposition, lipid metabolic disorders and liver and gut histology, and increased gut bacterial diversity in spotted sea bass.

This experiment investigated the effects of Astragalus membranaceus polysaccharides (AMP) on growth, physiological and biochemical parameters, and the expression of lipid metabolism-related genes in spotted sea bass, Lateolabrax maculatus. A total of 450 spotted sea bass ( g) were divided into six groups and were given diets with different levels of AMP (0, 0.2, 0.4, 0.6, 0.8, and 1.0 g/kg) for 28 days, respectively. Results indicated that dietary intake of AMP significantly improved fish weight gain, specific growth rate, feed conversion, and trypsin activity. Meanwhile, fish fed with AMP manifested significantly higher serum total antioxidant capacity and activity of hepatic superoxide dismutase, catalase, and lysozyme. Lower triglyceride and total cholesterol were noted in fish fed with AMP ( ). Moreover, hepatic ACC1 and ACC2 were downregulated by dietary intake of AMP, and PPAR-α, CPT1, and HSL were upregulated accordingly ( ). Parameters with significant difference were analyzed by quadratic regression analysis, and results showed that 0.6881 g/kg of AMP is the optimal dosage for spotted sea bass in size ( g). In conclusion, dietary intake of AMP can improve the growth, physiological status, and lipid metabolism of spotted sea bass, thereby indicating its promise as a potential dietary supplement.