Oral vaccination represents a transformative approach for disease prevention in rainbow trout aquaculture, offering the promise of mass immunization with minimal handling stress and improved welfare. As rainbow trout remain a cornerstone species in global aquaculture, infectious diseases such as bacterial (e.g., Yersinia ruckeri, Aeromonas salmonicida ) and viral (e.g., IHNV, VHSV) pathogens pose persistent threats to productivity and sustainability. Traditional injection and immersion vaccines, while effective, are labor-intensive and stressful, especially for large-scale operations. Oral vaccines, if optimized, could revolutionize disease management by enabling scalable, welfare-friendly immunization strategies. Oral vaccination offers economic and welfare advantages, but efficacy must be optimized to match injection methods. Mechanized feed delivery and improved formulations are key to enhancing cost-effectiveness. Common pain points for oral vaccines in rainbow trout include significant antigen degradation in the gastrointestinal tract, leading to diminished vaccine efficacy; the risk of oral tolerance induction due to repeated low-dose exposure, which may blunt immune responses; and lower cost-effectiveness due to variable protection compared to injection methods. Cutting-edge trends in this field involve the use of novel encapsulation strategies (alginate-chitosan, PLGA, starch hydrogels), bio-encapsulation with live feeds like Artemia salina , recombinant bacterial vectors delivering DNA vaccines, and the emerging application of mRNA- lipid nanoparticle vaccine platforms, all aimed at enhancing mucosal immune responses while overcoming stability and tolerance challenges. The most important immunity in oral vaccination of rainbow trout involves a combination of robust humoral and cellular responses. Key elements include the production of specific antibodies (IgM and IgT), activation of T-cells, and upregulation of cytokines. While oral vaccines require higher doses and may benefit from booster administrations, they offer significant protection and are a promising strategy for enhancing fish health in aquaculture
Nazari et al. (Sun,) studied this question.