Study on muscle fiber characteristics, metabolic enzymes and gene expression of caudal stalk of golden-backed carp (Cyprinus carpio var. Jinbei)

Golden-backed carp (Cyprinus carpio var. Jinbei) is a common carp that has lived in rice fields for many generations through long-term natural and artificial selection. In order to promote its paddy field breeding model and provide data supports for the breeding of improved varieties by this model, we analyzed the caudal stalk muscle fibers, related metabolic enzymes and gene expressions by using histology, enzymology and molecular biology methods, and explored the adaptive characteristics of caudal stalk muscle growth under the shallow ecological conditions of rice field. The results show that the diameter of caudal stalk muscle fiber in paddy field group was larger than that in pond group at flowering stage and harvest stage with significant differences (P<0.05). The cross-section area of caudal stalk muscle fiber in paddy field group was larger than that in pond group at flowering stage and harvest stage, with significant differences at harvest stage (P<0.05), while the density of caudal stalk muscle fiber in paddy field group was smaller than that in pond group. There were significant differences at harvest stage (P<0.05). The activities of lactate dehydrogenase (LDH), catalase (CAT) and Ca²⁺-ATPase in metabolic enzymes were higher in paddy field group than in pond group at flowering stage and harvest stage. The expression level of peroxisome proliferation-activated receptor γ-coactivator α (PGC-1α) gene in paddy field group was significantly higher than that in pond group (P<0.05). The results reveal that the expression levels of adenylate activated protein kinase (AMPK) and silence-regulating factor 1 (SIRT1) gene in paddy field group were significantly lower than those in pond group at flowering stage and harvest stage (P<0.05). The resistance movement of the caudal stalk of golden-backed carp in rice field caused muscle hypertrophy, which was related with the activation of protein synthesis pathway, while its endurance exercise, was related with the mitochondrial biosynthesis. The higher PGC-1α expression level of golden-backed carp in rice flowering stage may be related with the increase of rice flowering, insects, biodiversity and biomass.