Effects of acute flow velocity stress on oxygen consumption rate, energy metabolism and transcription level of mandarin fish (Siniperca chuatsi)

This study aimed to investigate the impact of acute velocity stress on the exercise physiology of mandarin fish (Siniperca chuatsi). Initially, the relative critical swimming speed (U’_crit) was estimated to be around 4.87 body lengths per second (bl/s), while the relative burst swimming speed (U’_burst) reached approximately 8.60 bl/s. Then, the results showed that as the flow velocity increased, the oxygen consumption rate (MO₂) of mandarin fish gradually elevated, while the cost of transport (COT) displayed a decreasing trend. Subsequently, four groups were established for the experiment, including control group (0 %U_crit), low flow velocity (20 %U_crit), medium flow velocity (50 %U_crit) and high flow velocity (80 %U_crit). The results showed that with the increase of flow velocity, the content of muscle glycogen decreased gradually and the content of muscle lactate increased significantly. Furthermore, the results of serum myocardial enzymes and antioxidant enzymes showed that the levels of creatine kinase (CK), total antioxidant capacity (T-AOC) and glutathione peroxidase (GSH-Px) exhibited an initial increase followed by a decrease. During the examination of the gills, the highest level of Na⁺-K⁺-ATPase was reached at 80 %U_crit, while the content of malondialdehyde (MDA) was significantly reduced. Additionally, transcriptomic sequencing was conducted on 0 %U_crit and 80 %U_crit groups, resulting in the identification of 101 upregulated genes and 116 downregulated genes. KEGG enrichment analysis revealed that the differentially expressed genes (DEGs) were significantly enriched in lipid metabolism and signal transduction. Finally, it was observed that the MAPK signaling pathway within the signaling transduction pathway exhibited the highest number of annotated DEGs. In general, it can be inferred that mandarin fish may regulate lipid peroxidation levels, and MAPK signaling pathway as an adaptive response to mitigate the effects induced by acute velocity stress. The above research is of great significance for improving the farming method of mandarin fish.