Feed Type Modulates Metabolic Responses and Thermal Tolerance of Mandarin Fish (Siniperca chuatsi) Under Warming Conditions

To investigate how feed type modulates the metabolic adaptation of mandarin fish (Siniperca chuatsi) acclimated to different temperatures, we compared the physiological responses of fish fed artificial feed (AF) and natural live feed (NF) across four acclimation temperatures (28, 30, 32, and 34 °C) by integrating oxygen consumption rate (MO2) measurements, gill metabolomic profiling, and thermal tolerance testing. The results showed that MO2 increased with rising temperature in both groups and that the AF group exhibited significantly higher MO2 than the NF group at all the tested temperatures (p < 0.01). Metabolomic analysis revealed a clear separation of metabolite profiles between the two feed groups at all acclimation temperatures. At normal temperatures (28–30 °C), metabolic differences were mainly associated with energy-supplying pathways such as glycolysis/gluconeogenesis and glycerolipid metabolism, whereas at high temperatures (32–34 °C), pathways related to neuroregulation and membrane signaling—including phototransduction, proximal tubule bicarbonate reclamation, carbon metabolism, the phosphatidylinositol signaling system, and pathways of neurodegeneration—were preferentially enriched. A set of pathways—including serotonergic synapse, Fc gamma R-mediated phagocytosis, and phospholipase D signaling—was overrepresented among the AF–NF differential metabolites at all temperatures, reflecting a persistent feed-associated effect. Redundancy analysis (RDA) indicated that the constrained model explained 43.02% of total variation and that feed type accounted for 80.48% of this explained variance (approximately 34.6% of total variation), exceeding the effects of MO2 and temperature. Functionally, the AF group exhibited a significantly lower critical thermal maximum (CTmax) than the NF group (p < 0.05), whereas the lethal thermal maximum (LTmax) did not differ between groups (p > 0.05), indicating that artificial feed is associated with reduced sublethal heat tolerance but does not alter the ultimate thermal limit. Collectively, these results provide correlative evidence that artificial feed is associated with an elevated metabolic phenotype and reshapes gill metabolite profiles in mandarin fish, which may contribute to impaired thermal resilience under warming conditions. This study provides a basis for optimizing nutritional strategies to improve the climate resilience of this species under climate change.