Impact of Starfish Predatory Pressure on the Immune and Antioxidant Functions of Sea Cucumber Apostichopus japonicus

Abstract

This study simulated the effects of direct predatory pressure, indirect predatory pressure, and conspecific injury signals on sea cucumber (Apostichopus japonicus) to determine changes in the activity of immune defense enzymes (lysozyme, acid phosphatase, alkaline phosphatase) and antioxidant stress enzymes (catalase, superoxide dismutase, malondialdehyde). Samples of sea cucumber juveniles were collected at 3 h, 12 h, 72 h, and 96 h post predatory stress, and six enzymes related to immune defense and antioxidant stress were selected for activity assays, namely, lysozyme (LZM), acid phosphatase (ACP), alkaline phosphatase (AKP), superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA). The results indicate that under direct predatory pressure, the activity of catalase in sea cucumbers was significantly higher than that of the control group at 3 h (P < 0.05), while the activities of acid phosphatase, alkaline phosphatase, and catalase were significantly lower at 72 h (P < 0.05). Under indirect predatory pressure, the activity of malondialdehyde in sea cucumbers was significantly higher than that of the control group at 12 h (P < 0.05), the activity of alkaline phosphatase was significantly higher at 72 and 96 h (P < 0.05), the activity of catalase was significantly lower at 72 h, and the activity of superoxide dismutase was significantly higher at 72 h (P < 0.05). Under the influence of conspecific injury signals, the activity of malondialdehyde in sea cucumbers was significantly higher than that of the control group at 12 h (P < 0.05), and the activity of superoxide dismutase was significantly higher at 96 h (P < 0.05). The sea cucumber enhanced its antioxidant capacity 3 h after facing a predator, while its immune defense mechanism was suppressed at 72 h. When facing indirect predatory pressure, the sea cucumber may have made immune and antioxidant preparations for the arrival of unknown risks. The experimental results show that predatory pressure has a significant impact on the immune and antioxidant functions of sea cucumbers, which may be related to the physiological state and environmental adaptability of the sea cucumber. This study provides a new perspective for understanding how sea cucumbers cope with predatory pressure in the natural environment and offers theoretical support for the cultivation management of sea cucumbers.