Physiological and immune response in the gills of Litopenaeus vannamei exposed to acute sulfide stress

Sulfide is a harmful environmental pollutant that affects the survival and immunity of shrimps. The gill is important for shrimp respiratory and osmotic adjustment, the physiological and immune homeostasis of the organ can be influenced by sulfide. In this study, we investigated the acute toxicity of sulfide (5 mg/L) on the morphology, physiological and immune response in the gills of Litopenaeus vannamei. H&E stain showed that sulfide stress damaged the gills histological structure. Specifically, osmoregulation capacity including of Na+/K+-ATPase and Ca2+/Mg2+-ATPase activity was both increased at 6 h and 12 h, and decreased at 72 h; the contents of free amino acid including of Gly, Pro, Ser, Thr and Ala were decreased at 72 h. Respiratory metabolic enzymes, such as cytochrome c oxidase and succcinate dehydrogenase activity was decreased at 12 h-72 h, while fumarate reductase and lactate dehydrogenase activity kept a higher level at 12 h-72 h. Significant variations in the activities of immune enzymes (acid phosphatase, alkaline phosphatase, total antioxidant capacity and lysozyme). The expression of immune-related genes (heat shock protein 70, thioredoxin and caspase-3) was increased at first and then decreased, while hypoxia inducible factor 1α kept a higher level at 6 h-72 h. These results revealed that sulfide stress influenced the L. vannamei gills physiological and immune function by damaging histological structure, and confusing osmoregulation, respiratory metabolic and immune capacity.