Advances in Vaccine Adjuvants for Teleost Fish: Implications for Aquatic Welfare and the Potential of Nanoparticle-Based Formulations

Abstract

Vaccine adjuvants are crucial for reinforcing the immunogenicity of vaccines. Therefore, they are widely used in the aquaculture sector as vaccine components, facilitating the efficient prevention of infectious diseases and promoting sustainable teleost fish growth. Despite their benefits, there has been a growing concern about the potential adverse effects of vaccine adjuvants in teleost fish, connoting a valid impact on their overall health and welfare. Among the adjuvants used in aquaculture vaccinology, nanoparticle-based formulations have given rise to a promising new alternative to traditional options, such as oil-based emulsions and aluminum compounds, offering the benefit of minimizing relevant side effects. The aim of this paper was to review the current status of the adjuvants used in aquaculture, provide a description and an evaluation of their mode of action and side effects, and explore the potential use of nanoparticle formulations as adjuvants to improve the efficacy of aquaculture vaccines. By demonstrating and assessing the equilibrium between teleost fish welfare and immunological efficacy, this review presents a collective perspective that will assist in establishing a framework for the utilization of effective species-specific practices around adjuvant use in aquaculture, while also addressing the challenges of welfare-friendly immunization.

Keywords: adjuvants; aquaculture; granulomas; health; immunization; inflammation; lesions; nanoparticles; side effects; sustainability; teleost fish; vaccines; welfare.

Figure 1

An overview of all elaborations made in the two-signal model to effectively explain the mode of action behind several vaccine adjuvants. An effective immunization is usually the result of a well-orchestrated immune response, and thus, the synergistic effect of antigens and vaccine adjuvants facilitating certain signals can aid in eliciting a robust and long-lasting protective effect.

Figure 2

A schematic illustration showcasing the main types of vaccine adjuvants used conventionally so far in teleost fish vaccinology.

Figure 3

Potential side effects of the current adjuvanted injectable vaccines in teleost fish. In severe cases, the physiological functioning of the digestive system and thus the growth rate can be impaired, potentially undermining animal welfare and lowering the quality of aquatic food products.