Abstract
<p><strong>Background: </strong>The excessive use of antibiotics in shrimp aquaculture cause severe ecological damage. Immunostimulant probiotics are an alternative prophylactic treatment to enhanceantioxidant and immune response to reduce mortality induced by pathogenic microbes. <strong>Objective: </strong>This study investigated the effect of live yeast <em>Debaryomyces hansenii</em> incorporated in diet and in culture water on survival and expression of the antioxidant and immune-related genes in <em>Penaeus vannamei</em> juvenile shrimp. <strong>Methodology: </strong>Shrimp were fed daily for 10 days with treatments of different doses and a post-infection with <em>Vibrio parahaemolyticus</em> as follows: a) control (-) without feed additives and non-infected; b) control (+) without feed additives and infected; c) <em>D. hansenii</em>, 1×10<sup>6</sup> CFU g<sup>-1</sup> feed; d) inulin, 2.5 mg g<sup>-1</sup> feed; e) <em>D. hansenii</em>, 1×10<sup>6</sup> CFU g<sup>-1</sup> feed + inulin, 2.5 mg g<sup>-1</sup> feed; f) <em>D. hansenii</em>, 2×10<sup>6</sup> CFU g<sup>-1</sup> feed + 1×10<sup>6</sup> CFU mL<sup>-1</sup>; g) <em>D. hansenii</em>, 4×10<sup>6</sup> CFU g<sup>-1</sup> feed + 1×10<sup>6</sup> CFU mL<sup>-1</sup>. Relative gene expression of lysozyme (<em>LYS</em>), glutathione peroxidase (<em>GPX</em>), and superoxide dismutase (<em>SOD</em>) were determined in shrimp muscle and hepatopancreas previous to challenge with <em>V. parahaemolyticus</em>. <strong>Results: </strong>Juvenile shrimp increased the resistance to <em>V. parahaemolyticus</em> infections significantly more than untreated shrimp after <em>D. hansenii</em> administration in feed and water, and mixed with inulin. Relative gene expressions of <em>LYS</em> and <em>SOD</em> increased significantly in shrimp muscle after treated with<em> D. hansenii</em> and <em>D. hansenii </em>+ inulin, respectively. <em>SOD</em> and <em>GPX</em> were significantly expressed in shrimp hepatopancreas<em>.</em> <strong>Implications: </strong>The findings provide new insights to apply yeast immunostimulants in reared shrimp to increase immune response and survival against experimental bacterial infections. <strong>Conclusions:</strong> In this study, juvenile shrimp exposed to additive immunostimulants increased gene expression in shrimp tissues, muscle and hepatopancreas, and the dose of 1×10<sup>6</sup> CFU g<sup>-1</sup> of <em>D. hansenii</em> in feed was sufficient to increase shrimp survival against <em>V. parahaemolyticus</em> infection.</p>
Highlights
Aquaculture is the fastest growing food production industry
Cell density was adjusted to 1×108 CFU mL-1, which was confirmed by counting colony forming units (CFU) on plate serial dilutions of yeast cultures and incorporated in experimental diets at different concentrations
After 10 days of culture with feed additives, juvenile shrimp were infected with a single exposure to V. parahaemolyticus (Figure 1)
Summary
Aquaculture is the fastest growing food production industry. In 2016 finfish production was 54 million t; 17.1 million t of mollusk and 7.9 million t of crustacean species. (FAO, 2018). Despite the explosive growth in world production of farmed shrimp, problems have occurred related to deterioration of environmental conditions (Gyan et al, 2020) and economic losses due to diseases (Balcázar et al, 2007; Srinivas et al, 2016) caused mainly by Vibrio bacteria and viruses in a deteriorated pond environment (Lo et al, 2003). It is estimated that around 20% of disease losses in shrimp aquaculture have been caused by bacterial pathogens (Flegel, 2012; Tran et al, 2018). Antibiotics and disinfectant agents are used in commercial shrimp hatcheries to control pathogenic microbes and improve shrimp growth (Gatesoupe, 1999; Balcázar et al, 2006). The use of some antibiotic agents has been prohibited in aquaculture in many countries due to their persistence, carcinogenic effects in some organisms, antibiotic residues in aquatic animals and surroundings, and the potential impact on human (Gatesoupe, 1999; Verschuere et al, 2000)
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