Effects of Acute Heat Stress and Hypo-Salinity Exposure on Sea Cucumber Apostichopus japonicus by Widely Targeted Metabolomics Analysis

Temperature and salinity are key environmental factors for sea cucumber (Apostichopus japonicus) aquaculture. To better understand the molecular regulation mechanisms of A. japonicus under extreme environmental conditions, we collected metabolomic data from a control group (C: 16 °C, 30 salinity), a heat-stress group (HT: 30 °C, 30 salinity), a hypo-salinity group (LS: 16 °C, 20 salinity), and a heat plus hypo-salinity group (HL: 30 °C, 20 salinity). Liquid chromatography–mass spectrometry-based metabolomics was used to measure the changes in endogenous metabolites in the body wall of A. japonicus and detect differential metabolites and associated metabolic pathways. The results of metabolomic profiling identified a total of 349 secondary metabolites, enriched mainly in unsaturated fatty acid metabolism, cAMP signaling pathway, pantothenic acid and coenzyme A biosynthesis, as well as vitamin metabolism. Compared to the control group, levels of amino acids and lipids were enhanced during adaptation to high-temperature stress (HT and HL groups). Levels of pantothenic acid content increased in the LS group compared with its content in the control group, which suggests that stress promoted the TCA cycle in the body of A. japonicus, providing energy for movement. A. japonicus may adjust energy metabolism by altering pathways or adapt to environmental changes by regulating the activities of certain enzymes to maintain life activities and metabolic homeostasis. In response to these stresses, A. japonicus metabolism increased to bolster its antioxidant capacity and maintain cellular homeostasis and organismal stability. These results clarified the complex physiological processes involved in the response to stress and the maintenance of metabolism of the A. japonicus. This study provides novel insights into the metabolic regulation mechanisms that enable A. japonicus to cope with heat and hypo-salinity stresses.