Is the Nutritional Value of Fish Fillet Related to Fish Maturation or Fish Age? Integrated Analysis of Transcriptomics and Metabolomics in Blunt Snout Bream (Megalobrama amblycephala).

Background/aims: Fish is a protein-rich food and is increasingly favored by consumers. It has been well recognized that the flesh composition of fish is closely related to its maturation and growth stage, but few studies have explored these differences. Additionally, hormone residues in fish after artificial induction of reproduction also attract consumer concern. In this study, we attempt to address these concerns by using a combination of transcriptomics and metabolomics analyses to identify key regulated pathways, genes, and metabolites that may affect the flesh nutrition of one typical aquaculture species in China, blunt snout bream (Megalobrama amblycephala).

Methods: The four groups of fish were used for transcriptomics and metabolomics analyses, including one-year-old immature (group I), two-year-old immature (group II), two-year-old mature (group III) and successfully spawned (group IV) female M. amblycephala after artificial induction of reproduction.

Results: We identified a total of 1460 differential compounds and 1107 differentially expressed unigenes in muscle among the different groups. Differential metabolites related to fish age (group II vs group I, group III vs group I) were largely enriched in "Glycerophospholipid metabolism", "Linoleic acid metabolism", "α-Linolenic acid metabolism", and "Biosynthesis of unsaturated fatty acids". Between these two pairwise comparisons, metabolites that are beneficial to human health, such as docosapentaenoic acid, α-Linolenic acid, eicosapentaenoic acid, and docosahexaenoic acid were found to be significantly decreased in two-year-old (group II, group III) compared with one-year-old (group I) M. amblycephala. Only one differential metabolite related to fish maturation, a triglyceride, was detected between groups III and II. Transcriptomics data showed that differently expressed genes (between group III vs group II, group III vs group I) related to maturation were highly enriched in "Cell adhesion molecules (CAMs)", "Sphingolipid metabolism" and "Phagosome". DEGs (between group II vs group I, group III vs group I) relating to fish age were enriched in the "cGMP-PKG signaling pathway", "FoxO signaling pathway", and "AMPK signaling pathway". The gene-metabolite interaction network showed pivotal genes, including fumarate hydratase and GNPAT, which played a major role in the regulation of glycerphospholipid metabolism. The nutritional components were also measured, which verified the metabolomics results. Moreover, the metabolomics results showed that after 24 hours of artificial hormone injection, the drug was completely metabolized.

Conclusion: Integrated analysis demonstrated that the nutrition value of fish fillet was much more related to fish age compared with maturation status in M. amblycephala females.