Analysis of metabolic characteristics of highly resistant grass carp bred on the basis of constitutive expression level of innate immune molecules.

Grass carp, recognized as China's largest freshwater fish, has been severely impacted by grass carp reovirus (GCRV). Consequently, the development of new grass carp strains with heightened resistance to GCRV is a focal point of contemporary research. This team, utilizing a genetic network and map of grass carp anti-GCRV genes centered on innate immune molecules, established over several years, has categorized the original Xiangjiang River grass carp into groups based on differences in the innate immune molecules' constitutive expression levels, primarily in the complement system C3. Following multiple GCRV challenge experiments, a highly resistant strain, Xiangkang No. 1, was successfully bred. In this study, Xiangkang No. 1 (KX) grass carp and the progeny of common Xiangjiang original (PT) grass carp were used. qPCR analysis revealed distinct expression levels of immune molecules (C3, BF/C2, etc.) between the two types, with KX grass carp showing significantly higher expression in liver tissue. Furthermore, the levels of GSH-PX, T-SOD, and CAT in the liver tissue of KX grass carp were notably higher than in PT grass carp, indicating superior antioxidant capacity in KX grass carp. This correlation suggests a positive relationship between the expression of immune molecules in the liver and antioxidant capacity. Metabolome analysis identified 93 distinct metabolites in the liver of both grass carp types, predominantly categorized into nucleosides, nucleotides, nucleotide analogues, organic acids and derivatives, organic oxygen compounds, and lipid-related molecules. The enrichment of KEGG pathways indicated a concentration of metabolites in the metabolism of cofactors and vitamins, amino acid metabolism, and carbohydrate metabolism. Notably, L-Glutamic acid was significantly up-regulated in KX grass carp and was implicated in multiple pathways, suggesting its role as a targeted metabolite enhancing resistance in grass carp. Thus, this study hypothesizes a significant link between the basal expression of immune factors, antioxidant capacity, and L-Glutamic acid in grass carp. These findings provide insights into "immune metabolism" and support the breeding of resistant grass carp strains.