Comparative transcriptomic analysis reveals immune regulation in mandarin fish (Siniperca chuatsi) under high- and low-temperature.

The mandarin fish (Siniperca chuatsi) is an economically important freshwater species in China, with an optimal growth temperature ranging from 18 to 25°C. Fluctuations in water temperature, however, can increase its susceptibility to disease. To compare the immunoregulatory response characteristics of mandarin fish under high- and low-temperature conditions and to elucidate their shared and distinct mechanisms, 20°C was used as the control, and the temperature was gradually adjusted from 20°C to 10°C and 30°C at a rate of 2°C/day; after reaching the target temperatures, fish were maintained for an additional 7 days as experimental groups. Liver transcriptomic profiles were analyzed, key genes involved in significantly enriched pathways were examined. KEGG enrichment analysis showed that both high- and low-temperature treatments commonly affected the Cytokine-cytokine receptor interaction pathway, but exhibited distinct regulatory characteristics. High temperature mainly induced upregulation of chemokines (CCL, CXCL) and pro-inflammatory cytokines (e.g., il1β, tnf-α), whereas these responses were attenuated under low temperature. In addition, several cytokine receptor genes (including IL and TNF receptor family members) exhibited opposite expression trends between treatments. RT-qPCR validation confirmed the transcriptomic patterns, with significant upregulation of tnf-α, il1β, and il10 under high temperature, while no marked changes were observed under low temperature. Furthermore, high temperature significantly enriched IL-17 signaling and leukocyte chemotaxis pathways, indicating enhanced inflammatory activation and immune cell recruitment, whereas low temperature was mainly associated with monocyte migration and metabolic adjustment. PPI network analysis further supported distinct regulatory architectures of cytokine signaling under different thermal conditions. Overall, high temperature (30°C) predominantly induces activation of inflammatory responses, whereas low temperature (10°C) tends to regulate metabolism and maintain immune homeostasis. This study provides new insights into the molecular mechanisms underlying immune responses of fish adapting to different environmental temperatures.