The combined effect of acute hypoxic stress and feeding status on the metabolism of yellow catfish (Pelteobagrus fulvidraco)

Metabolism is one of the most important physiological processes in fish that changes daily depending on the variability of disparate factors. Dissolved oxygen and feeding status are critical to the growth and metabolism of fish. In this study, the effects of dissolved oxygen and feeding status, as well as their interaction on the blood biochemistry and metabolism of yellow catfish (Pelteobagrus fulvidraco) were investigated using a two-factor test. At a dissolved oxygen content of 1.2 mg mL−1, yellow catfish were exposed to hypoxia for 48 h and divided into four experimental groups: normoxia (6.5 mg L−1)-fasting group (C; Control group); normoxia-feeding group (F); hypoxia (1.2 mg L−1)-fasting group (H); and hypoxia-feeding group (FH). Analysis revealed that both hypoxia and feeding caused a short-term increase in the number of red blood cells and hemoglobin concentration in yellow catfish, thereby increasing the oxygen-carrying capacity of the blood. After feeding, the metabolic activity in yellow catfish showed a trend of rising and then falling. Following hypoxia, yellow catfish activated anaerobic glycolysis to provide the energy required by the body, and the mode of metabolism in yellow catfish gradually converted from aerobic to anaerobic. Moreover, the activity of respiratory metabolism enzyme succinate dehydrogenase (SDH) tended to decrease and then increase, while that of lactate dehydrogenase (LDH) tended to increase and then decrease, showing opposing trends. Furthermore, the liver glycogen was mobilized, blood glucose levels increased, and lactic acid accumulation occurred in the short term. Meanwhile, the hypoxia-inducible factor (hif-1α) was activated, the expression of glucose metabolism-related genes (epo, hk1, pfkla, pkma, and gk) dramatically increased, and the activities of the three key enzymes involved in glycolysis (HK, PFK, and PK) were elevated for a short period of time. In conclusion, both hypoxia and feeding altered blood biochemical and metabolic responses in yellow catfish over time, and the metabolic responses were more intense in the post-feeding hypoxia group.