Integrated analysis of muscle developmental features and molecular characterization of myogenic regulatory factors in two hybrid breams.

Distant hybridization combines beneficial genes from different species to create high-quality germplasm with altered phenotypes and genotypes. In our previous study, two fast-growing hybrid breams (BTBB and BBTB) were developed through a multi-step breeding strategy involving distant hybridization between blunt snout bream (Megalobrama amblycephala, 2n = 48, BSB, ♀) and topmouth culter (Culter alburnus, 2n = 48, TC, ♂), followed by two rounds of backcrossing. To elucidate the mechanisms of muscle development and rapid growth, we compared growth performance, muscle texture, antioxidant enzyme activities, and the expression of myogenic regulatory factor (MRF) genes between the hybrids and their parents. The results showed that both BBTB and BTBB had significantly greater body weight and body length than BSB (p < 0.05). Histological analysis showed that the two hybrid breams had significantly lower muscle fiber density (p < 0.05) and significantly larger muscle fiber diameter than BSB (p < 0.05). Muscle texture analysis indicated that BBTB had higher adhesiveness than BSB, whereas BTBB exhibited significantly greater springiness than BSB. Antioxidant analysis showed that, compared with BSB, MDA levels were significantly lower in BBTB and BTBB (p < 0.05), whereas CAT, SOD, and GSH levels were higher. Sequence analysis showed that the full-length cDNA sequences of myod, myog, myf5, and myf6 were highly conserved between the hybrid offspring and their parents. RT-qPCR analysis revealed that the expression levels of MRFs and mstn were relatively high in the muscle tissues of both BTBB and BSB, whereas mstn expression was lower in BTBB than in BSB, suggesting that MRFs and mstn may act coordinately in the regulation of rapid growth in BTBB. In contrast, the expression levels of MRFs and mstn in BBTB were significantly lower than those in BSB, suggesting that MRF expression may increase transiently during rapid growth and then decline. Overall, the two hybrid breams exhibited distinct molecular regulatory patterns, and their superior muscle phenotypes may be associated with muscle fiber development, enhanced antioxidant capacity, and the balance between positive myogenic regulation and mstn-mediated negative regulation. These findings indicate that BBTB and BTBB are promising germplasm resources for aquaculture breeding.