Immune Responses to Fish Pathogens

Fish rely on an intricate interplay of innate and adaptive defences to resist viral, bacterial and parasitic pathogens in both wild and cultured populations. Initial barriers include mucosal surfaces, skin secretions and antimicrobial peptides, while cellular components such as macrophages, neutrophils and natural killer–like cells execute phagocytosis and cytotoxicity. Soluble factors of the innate system—complement proteins, acute-phase reactants and pro-inflammatory cytokines—mediate pathogen recognition and recruit effector cells. Adaptive responses involve the production of specific immunoglobulins, T-cell activation via MHC presentation and the generation of immunological memory. Environmental stressors, including water temperature, stocking density and vaccination, modulate these pathways and influence disease outcome. Advances in functional genomics, imaging and biomarker development now permit a mechanistic understanding of how fish orchestrate immune defences against diverse aquatic pathogens.

Research from Nature Portfolio

Foundational studies have demonstrated that dietary administration of the probiotic Bacillus subtilis can fortify intestinal barrier function and attenuate inflammation in grass carp challenged with Aeromonas hydrophila. Probiotic treatment prevented pathogen-induced disruption of tight junction proteins, maintained ATPase activities critical for ion transport and suppressed up-regulation of pro-inflammatory cytokines. This work established a microbial-based strategy to modulate mucosal immunity and reduce disease susceptibility in aquaculture settings.

Research from all publishers

Multi-omics analyses in the Chinese soft-shelled turtle during Aeromonas hydrophila infection have revealed stage-specific host responses. At early infection, transcriptomic shifts in chemokines and interleukins coincide with fluctuations in tryptophan and nicotinate metabolism; later stages feature up-regulation of T-cell signalling genes alongside amino acid and pyrimidine pathway engagement. In golden pompano challenged with Streptococcus agalactiae, an oxidative burst marked by elevated reactive oxygen species triggers the TNF-α/NF-κB cascade. Subsequent induction of antioxidant enzymes (SOD, CAT, GPx) and cytokine expression underpins a coordinated inflammatory response that peaks at defined post-infection intervals. A complementary line of research in largemouth bass has evaluated a novel herbal formula combining Galla Chinensis, mangosteen shell, pomegranate peel and Scutellaria baicalensis extracts. This botanical blend exhibits potent in vitro antibacterial activity against aquatic pathogens and, in vivo, raises hepatic lysozyme, acid phosphatase and antioxidant enzyme activities. Concurrent up-regulation of IL-1β, TNF-α and MyD88 mRNAs correlates with enhanced survival following Aeromonas challenge, highlighting the promise of phytogenic immunostimulants.

Immune Responses to Fish Pathogens publication trend

The graph below shows the total number of articles in immune responses to fish pathogens across all publications each year (not limited to Nature Index journals).

Technical terms

Innate immunity: The non-specific first line of defence involving barrier structures, phagocytic cells and soluble mediators that act rapidly upon pathogen encounter.

Adaptive immunity: The antigen-specific arm of the immune system characterised by lymphocyte activation, antibody production and immunological memory.

Phagocytes: Immune cells such as macrophages and neutrophils that ingest and destroy pathogens via endocytosis.

Cytokines: Small signalling proteins, including interleukins and tumour necrosis factors, that orchestrate immune cell communication and inflammation.

Tight junction proteins: Structural molecules (e.g. occludin, ZO-1) that seal epithelial cell contacts and maintain mucosal barrier integrity.

Transcriptomics: The large-scale study of RNA transcripts to elucidate gene expression changes under specific conditions.

Metabolomics: The comprehensive analysis of metabolites in a biological sample, revealing biochemical pathway alterations.

Reactive oxygen species (ROS): Highly reactive molecules derived from oxygen metabolism that function as antimicrobial agents and signalling mediators.

NF-κB signalling pathway: A central inflammatory cascade activated by stress or infection, leading to transcription of genes involved in immune responses.

References

1. Effect of Bacillus subtilis on Aeromonas hydrophila-induced intestinal mucosal barrier function damage and inflammation in grass carp (Ctenopharyngodon idella). Scientific Reports (2017).
2. Integrated time-series biochemical, transcriptomic, and metabolomic analyses reveal key metabolites and signaling pathways in the liver of the Chinese soft-shelled turtle (Pelodiscus sinensis) against Aeromonas hydrophila infection. Frontiers in Immunology (2024).
3. ROS Induced by Streptococcus agalactiae Activate Inflammatory Responses via the TNF-α/NF-κB Signaling Pathway in Golden Pompano Trachinotus ovatus (Linnaeus, 1758). Antioxidants (2022).
4. The combined effect of a novel formula of herbal extracts on bacterial infection and immune response in Micropterus salmoides. Frontiers in Microbiology (2023).