Changes in Survival Rate of the Shrimp Litopenaeus vannamei under Combined Stress during Waterless Live Transport and Defense System Responses

In order to explore the mechanism of oxidative and immune injury by which combined stress of acute cold exposure and air exposure during waterless live transport induces the death of Litopenaeus vannamei, oxidant stress injury and changes in related immune system indicators in the hepatopancreas in response to the combined stress were analyzed under conditions simulating actual transportation. The results showed that compared to the control group, the survival rate declined after acute cold + 9 h waterless stress. The level of reactive oxygen species (ROS) significantly increased in response to acute cold stress (P < 0.05), but declined in response to subsequent waterless stress. Meanwhile, the content of malondialdehyde (MDA) in the cold stress and combined stress groups was significantly higher than that in the control group (P < 0.05), and the maximum value was observed in the acute cold + 3 h waterless stress group. In addition, the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) increased with air exposure duration, reaching 2.82, 2.12 and 5.26 U/mg at 9 h, respectively. After 2 h resuscitation, they nearly returned to normal. In the combined stress group, the activities of the non-specific immune enzymes phenol oxidase (PO), peroxidase (POD) showed a downward trend, while the activities of acid phosphatase (ACP) and alkaline phosphatase (AKP) increased incessantly with air exposure duration, reaching their maximum at 9 h and nearly returning to normal after resuscitation. Furthermore, histopathological examination showed that slight decomposition of epithelial tubules and partial exfoliation of cells in the inner wall appeared in the acute cold + 9 h waterless stress group, which indicated that the defense system was damaged. As L. vannamei can increase its antioxidant enzyme activities and non-specific immune activities in response to environmental stress, intolerable stress can cause irreversible damage to the hepatopancreas and ultimately cause the death of L. vannamei.