Respiratory Metabolism and Metabolomics of Red Swamp Crayfish <i>Procambarus clarkii</i> Under Low Temperature Stress

In the integrated rice-crayfish aquaculture systems, crayfish Procambarus clarkii need to spend a long winter in the ring ditch, which is vulnerable to low temperature stress, especially in the northern part of China, where cold waves and other low-temperature climates are frequent. To study the metabolic response of P. clarkii to low temperature stress experimentally, the temperature was lowered from the control (23°C) to the low temperature group (9°C, 5°C, and 1°C) by slow and uniform cooling, and molecular and physiological samples were collected for measurement. The results showed that low temperature stress damaged the gill membrane and the epithelial layer of gill tissues, with an increase in vacuoles area and a reduced and irregular distribution of hemocytes. As the temperature decreased, the oxygen consumption rate, ammonia excretion rate and maximum metabolic rate of P. clarkii decreased gradually, the oxygen-nitrogen ratio decreased but still remained at a high level, and the metabolic energy supply substances were always mainly lipids and carbohydrates. The pyruvate kinase activity tended to increase with decreasing temperature under low temperature stress, while hexokinase, succinate dehydrogenase and lactate dehydrogenase activities decreased gradually. The 183 differential metabolites were screened in the low temperature group compared with the control mostly enriched in amino acid metabolism and citrate cycle metabolic pathways. In conclusion, under low temperature stress, the gill was damaged, respiratory metabolism decreased, and glycolysis was enhanced. Since the citrate cycle metabolism was suppressed, P. clarkii needed to resist low temperature stress by increasing the amino acid metabolism to provide more energy to maintain cellular activity. The results unraveled metabolic response mechanisms of metabolic response mechanism of P. clarkii to low temperature stress, and provided theoretical references for the selection and breeding of low-temperature-tolerant strains of P. clarkii.