Catalase protects Penaeus vannamei against WSSV by regulating redox homeostasis

White spot syndrome virus (WSSV) remains one of the most destructive viral pathogens in shrimp aquaculture. Reactive oxygen species (ROS) are required for innate immune signaling, but uncontrolled ROS accumulation can damage host tissues and compromise antiviral defense. Catalase (CAT) decomposes hydrogen peroxide and is therefore positioned to connect redox homeostasis with immune resilience during viral infection. Here, we cloned and characterized a CAT gene (Pv-CAT) from Penaeus vannamei and examined its role in the anti-WSSV response. Pv-CAT contained a 1563-bp open reading frame encoding a 520-amino-acid CAT-like protein with a predicted molecular mass of 58.83 kDa. Bioinformatic analyses indicated that Pv-CAT lacks a signal peptide and transmembrane region and retains typical features of antioxidant enzymes. Pv-CAT was expressed in all tested tissues, with relatively high levels in the hepatopancreas and hemocytes. Its expression changed markedly after WSSV infection, especially in barrier and immune-related tissues. Silencing Pv-CAT decreased intestinal CAT activity, promoted hydrogen peroxide (H₂O₂) accumulation and lipid peroxidation, disturbed the expression of antimicrobial peptide genes and JAK/STAT pathway-related genes, and reduced shrimp survival after WSSV challenge. These findings suggest that Pv-CAT contributes to antiviral resilience in P. vannamei by limiting oxidative injury and helping maintain immune-signaling balance during WSSV infection. The study provides evidence that antioxidant enzymes form an important part of the crustacean antiviral-defense network.