Characterization of metabolomic differences in peanut worm Sipunculus nudus between breeding and nonbreeding seasons

•First Characterization of S. nudus oocyte development by using metabolomics.•S. nudus may exhibit high anabolic ability to store nutrients during breeding season.•S. nudus may hold high activity of neurotransmitter precursor to regulate oocyte development. Peanut worm, Sipunculus nudus, is an important economic and ecological species. This study aims to characterize differences in the coelomic fluid of S. nudus between breeding and nonbreeding seasons. Animals were obtained in July and November. The diameter of oocytes was measured and analyzed. Results showed that the number of oocytes formed a primary peak at a diameter of approximately 160 μm in July, while almost all oocytes were below 50 μm in November. A metabolomics approach based on LC–MS and GC–MS was used to investigate differences in coelomic fluid and gain insights into the mechanisms underlying the oocyte development of S. nudus. In the metabolomics assay, 44 and 32 significantly differential metabolites were obtained via LC–MS and GC–MS (VIP > 1 and P