The metabolic responses of crucian carp blood to Cyprinid herpesvirus 2 infection

In recent years, Cyprinid herpesvirus 2 (CyHV-2) has severely affected the culture of crucian carp Carassius auratus gibelio, causing massive economic losses. However, the responses of crucian carp during infection with CyHV-2 have not been explored. In this study, physiological and biochemical indicators and enzyme activities of crucian carp before and after infection with CyHV-2 were analyzed. The number of white blood cells in the diseased fish was significantly increased. Compared to control group, red blood cell content, hemoglobin content, mean corpuscular volume, mean corpuscular hemoglobin content and mean corpuscular hemoglobin concentration in the experimental group were significantly decreased. In the diseased fish group, the levels of the glutamic-pyruvic transaminase, glutamic-oxalacetic transaminase, alkaline phosphatase, lactate dehydrogenase and urea nitrogen in the blood were also significantly increased compared to the control group. In addition, the activity of serum total antioxidant capacity, acid phosphatase, glutathione-S transferase and catalase in diseased fish were significantly higher than in the control group. LC-Q/TOF-MS analysis platform was used in this study for the first time to detect changes in the serum metabolome of crucian carp infected with CyHV-2. A total of 79 differential metabolites have been identified. Significant increases in concentrations were found for several carbohydrates (glucose, mannose, ribose, etc.), fatty acids (pentadecanoic acid, arachidonic acid, palmitic acid, eicosapentaenoic acid, hydroxylic tetracarbonate alkenoic acid, linoleic acid and its derivatives) and most of the amino acids and their derivatives. However, guanine, cytosine, uridine and VB2 were significantly decreased. KEGG pathways enrichment showed that amino acid metabolism and lipid metabolism were severely influenced. The above results provide a theoretical basis for the infection mechanism of CyHV-2