Physiological Responses and Mechanisms of the Sea Cucumber Apostichopus Japonicus Under Chronic Hypoxic Conditions

Abstract

Hypoxic conditions frequently occur during the cultivation of sea cucumbers (Apostichopus japonicus), negatively affecting various physiological processes and potentially leading to mortality. Most existing research on hypoxic stress in sea cucumbers focuses on acute hypoxic stress, yet hypoxic environments, once established, often persist for extended durations. In this study, we simulated realistic conditions by establishing dissolved oxygen (DO) levels of 2.0, 3.0, 4.0, 5.0, and 6.0 mg/L, with a control group at 7.0 mg/L, over an 18-day cultivation experiment. The oxygen consumption rate, survival rate, and weight gain rate of the sea cucumbers were measured. Additionally, sea cucumbers exposed to DO levels of 2.0, 4.0, and 7.0 mg/L were selected as the hypoxia group, the moderate hypoxia group, and the control group, respectively. Using transcriptomic, metabolomic, and integrative analyses, we investigated the response mechanisms of sea cucumbers under prolonged hypoxic conditions. The results showed that chronic hypoxia had detrimental effects on respiration, survival, and weight gain in sea cucumbers, with declines in oxygen consumption rate, survival rate, and weight gain rate as DO levels decreased. Sea cucumbers responded to chronic hypoxic stress primarily through regulating energy metabolism pathways and immune functions: glycolysis and the tricarboxylic acid cycle were inhibited, while energy production via fatty acid β-oxidation was enhanced. Regarding immune function, the regulation of amino acid metabolism, such as glutathione, enhanced cellular antioxidant and immune capacities to counteract oxidative stress. The present results revealed the response mechanisms of Apostichopus japonicus under long-term hypoxia stress at the molecular level, providing new insights into its survival strategies in hypoxic environments, as well as offering a basis for optimizing the aquaculture conditions of sea cucumbers.

Keywords: Apostichopus japonicus, Hypoxia, Response mechanisms, Transcriptomic analysis, Metabolomic analysis