Farmed shrimp are susceptible to different pathogens, such as bacteria, virus, parasites and fungi, but overall viral disease outbreaks have been responsible for the most significant economic losses (Lightner, Redman, Pantoja, Tang, Noble, Schofield, Mohney, Nuna & Navarro 2012). Among them, the White Spot Disease (WSD) has been the most devastating viral disease, leading to huge socio-economic impacts for shrimp farming worldwide. The etiologic agent, the White Spot Syndrome Virus (WSSV), can be highly virulent, causing mass mortality (80–100%) in ponds within few days (3 – 10 days) of the onset of clinical signs.
Biofloc technology is a sustainable alternative to shrimp farming, since it can reduce environmental impacts due to recycling nutrient and little water exchange. It is characterized as an intensive system, in which aquatic animals are reared at high densities. Aggregates of microorganisms, associated with particles, colloids, organic polymers and dead cells, are present in the water column with predominance of heterotrophic aerobic bacteria. The major advantage of biofloc is being considered as biosafe, because the introduction of pathogens into the system is less likely (Crab, Defoirdt, Bossier& Verstraete 2012; Cardona, Gueguen, Mgré, Lorgeoux, Piquemal, Pierrat, Noguier & Saulnier 2016).
Crustaceans do not display adaptive immune system. Nonetheless, their efficient defense responses are based on their innate immune system which comprises both cellular and humoral components (Hauton 2012). Moreover, their defense responses also rely on other biochemical pathways. Therefore, investigating molecular responses related to a variety of biological process, such as antioxidant defense responses, apoptosis, protein translocation, protein turnover and energetic pathways, may contribute to understand the molecular mechanisms involved in the overall response against pathogens, as well in the disruption of cellular biochemical, due to the onset of the pathogenic infection.
As part of the antioxidant defense system, superoxide dismutase (SOD) could be a target to be investigated. SOD catalyzes to harmless molecules the reactive oxygen intermediates (ROIs) produced after phagocytosis process, and can be used as a stress indicator (Smith et al. 2014).
As far as the invertebrate innate immune system is considered, one of the major response in crustacean is the prophenoloxidase (proPO) activating system, which is part of the biochemical synthesis of melanin, and comprises cytotoxic molecules in the host response to infection or trauma (Smith, Roulston & Dyrynda 2014). Besides the proPO gene itself, Xu, Wu & Zhang (2008) suggested that QM gene also participate in the proPO cascade. Apoptosis, an important response in immunity and in development, eliminating cells infected with virus and other pathogens (Smith et al. 2014), involves the product of QM, i.e., an apoptotic protein.
Therefore, in order to better understand the molecular responses upon WSSV infection in shrimp, Litopenaeus vannamei, we analyzed the transcript profile of selected target genes in experimentally challenged shrimp, kept in two different cultivation systems, biofloc and clear seawater. Additionally, we compared survival rates and addressed WSSV quantification in shrimp in both systems.