Abstract
For many years now, diet has been identified as a pivotal conditioner of health and immune status in both mammals and fish. Yet the extent to which diet composition or diet supplementation with immunostimulants affects the response to vaccination has been scarcely studied. In this study, we have carried out a series of different feeding experiments in rainbow trout (Oncorhynchus mykiss) to determine how diet composition can affect the antibody response to vaccination. For this, fish were fed the different supplemented diets or a control diet for 30 days. At that point, fish were immunized with different antigenic models through different administration routes and at day 30 post-immunization, fish were sacrificed and systemic specific antibody responses analyzed by ELISA. Antibody affinity was also determined in some cases. These experiments included diets supplemented with methionine or enriched with β-glucans or the probiotic microorganism Bacillus subtilis. The diets tested were selected based on preliminary in vitro experiments that demonstrated the capacity of these substances to increase B cell function in rainbow trout. Our results demonstrate that an optimized diet can improve the performance of vaccines in fish, being this especially useful for underperforming mucosal vaccines. The results presented will be useful for the design of holistic vaccination protocols that will not only focus on antigen optimization or administration regimes, but that will also include diet composition as an important factor to influence the outcome of the immunization strategy.