56 MARCH 2025 • WORLD AQUACULTURE • WWW.WAS.ORG Litopenaeus vannamei accounted for 61% of the 9.5 million tons of global shrimp production in 2022 (FAO, 2022). However, extremely intensive culture systems and climatic change have been documented to adversely impact shrimp production yield (Byer, 2021; Kibenge, 2019; Monier et al., 2023). According to Hein et al. (2022), these two factors might have contributed to environmental stress and the decline of water quality, which in turn led to severe disease infections. In fact, Vibrio induced diseases remain a major impediment to the shrimp culture industry (Flegel et al., 2009; Oanh & Phuong, 2012; Aguilera-Rivera et al., 2019; Lafferty et al., 2015; Yu et al., 2022). The widespread dissemination of Vibrio spp. in shrimp aquaculture ecosystems is attributed to their high proliferation rates and adaptability to environmental changes (BakerAustin et al., 2018). Litopenaeus vannamei depends on its innate immunity to combat pathogens such as White Spot Syndrome Virus (WSSV), Vibrio alginolyticus, V. cholerae, V. harveyi, and V. parahaemolyticus (de La Vega et al., 2007; Ali et al., 2023; Limkul et al., 2023). The expression levels of a series of innate immunity genes which encode antimicrobial and antiviral properties, are crucial for elucidating specific responses to microbial pathogenicity at the molecular level. To our knowledge, there is currently no information available regarding the activation and modulation of the innate immune response of shrimp cultured at varying salinity levels in response to V. harveyi infection. However, shrimp mortality has been reported to be highly linked to pathogenic infection and salinity stress. In this study, we aim to investigate the immunological response of L. vannamei to V. harveyi infection cultured at three salinity levels (5, 20, and 30 ppt). We assessed the survival rate and expression levels of immunity genes to determine which salinity level has made shrimp most susceptible towards V. harveyi infection, as well as to evaluate the expression patterns of bacterial toxin genes following pathogen exposure. Study Description We cultured juvenile shrimp (average of initial weight = 2 ± 0.04 g, mean ± SE) at 5 ppt, 20 ppt, and 30 ppt (control group) in the Institute of Aquaculture Tropical and Fisheries Sciences (AKUATROP), Universiti Malaysia Terengganu (UMT) for 60 days prior to Vibrio harveyi infection. To evaluate the responses of L. vannamei cultivated at three distinct salinity levels (5, 20, and 30 ppt) towards V. harveyi infection, we immersed the shrimp in 2.7 x 107 CFU mL−1 of pathogenic V. harveyi, and monitored their survival probabilities for 24 hours post-infection. Following the 24-hour challenge test, we extracted total RNA from the shrimp hepatopancreas prior to quantitative Polymerase Chain Reaction (qPCR) assays of 10 immune-related genes [c-type lectin (c-t), perleucine (Per), calpain-5 ASIA-PACIFIC CHAPTER ARTICLE: Achieving an Optimal Salinity: The Influence of Salinity Levels on the Immunity of Pacific Whiteleg Shrimp against Vibrio harveyi Infections Zulaikha Mat Deris and Li Lian Wong FIGURE 1. Acclimatization process of Litopenaeus vannamei post-larvae to different salinity levels. FIGURE 2. Pure culture of Vibrio harveyi on blood agar.
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