Comparison and mechanism analysis of fatty acid differences between backcross F2 derived from blunt snout bream (Megalobrama amblycephala,♀) × topmouth culter (Culter alburnus,♂) and its closely related species

Abstract

High-quality fatty acids are essential indicators of the nutritional value of aquatic fish. This study investigates the differences in muscle fatty acid composition and their nutritional implications by integrating physiological and transcriptomic analyses to elucidate the underlying regulatory mechanisms in the New Hybrid Bream (BBTB) compared with four closely related species: Megalobrama hoffmanni (MH), Megalobrama terminalis (MT), Megalobrama amblycephala (MA), and Culter alburnus (CA). A total of 21 fatty acids were identified in muscle tissue through gas chromatography, including 7 saturated fatty acids (SFAs) and 14 unsaturated fatty acids (UFAs). Among all species, palmitic acid (C16:0), oleic acid (C18:1n- 9), and linoleic acid (C18:2n- 6c) were the most abundant, accounting for 71.44 to 77.74% of the total fatty acids. Notably, BBTB exhibited a higher proportion of n- 6 polyunsaturated fatty acids (PUFAs), particularly linoleic acid, gamma-linolenic acid, arachidonic acid (C20:4n- 6), and eicosadienoic acid (C20:2). Subsequently, the expressions of fatty acid synthesis, degradation, and transporting related genes were examined to explore the mechanism of elevated PUFA in BBTB. The result exhibited that the expression of fatty acid synthesis key genes fasn, fads2, fads6, acacb, srebp1, acss2, and dgat2 genes of BBTB was significantly higher than that of other groups. Additionally, the expressions of pparα, pparδ, and pparγ which are critical regulators in the PPAR signaling pathway were significantly elevated in BBTB, suggesting their involvement in fatty acid synthesis, degradation, and oxidation. Further, transcriptomic analysis of BBTB liver further confirmed the gene expression results. Transcriptomic analysis of BBTB liver identified 125 differentially expressed genes (DEGs), with a subset associated with fatty acid metabolism, including pathways related to fatty acid degradation, PPAR signaling, and polyunsaturated fatty acid biosynthesis. KEGG enrichment analysis demonstrated significant enrichment of DEGs in lipid metabolism pathways, and COG and GO annotation further verified a high proportion of DEGs functioned in lipid transport, post-translational modifications, protein transformation, and chaperone activity. These findings provide valuable insights into the different values of BBTB and other examined group fishes and regulatory mechanisms governing lipid metabolism in BBTB, offering a foundation for improving the nutritional value of fish in aquaculture.