Gene expression profiles of white bass (Morone chrysops) and hybrid striped bass (M. chrysops x M. saxatilis) gill tissue following Flavobacterium covae infection

Authors: Andersen, Linnea; Abernathy, Jason; Farmer, Bradley; Lange, Miles; McEntire, Matthew - Matt; Rawles, Steven - Steve

Submitted to: Comparative Immunology Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2024
Publication Date: 4/25/2024
Citation: Andersen, L.K., Abernathy, J.W., Farmer, B.D., Lange, M.D., Mcentire, M.E., Rawles, S.D. 2024. Gene expression profiles of white bass (Morone chrysops) and hybrid striped bass (M. chrysops x M. saxatilis) gill tissue following Flavobacterium covae infection. Comparative Immunology Reports. 6:200144. https://doi.org/10.1016/j.cirep.2024.200144.
DOI: https://doi.org/10.1016/j.cirep.2024.200144

Interpretive Summary: Columnaris is a common disease that is devastating to wild and aquaculture-raised fish populations. The bacteria that causes columnaris, Flavobacterium spp., are present in essentially all freshwater environments, making it particularly difficult to prevent and treat infection. The initial stage of infection begins with the bacteria adhering to the protective or mucus, present on the exterior of fish skin and gill tissue. Hybrid striped bass (cross between white bass females and striped bass males) are a prominent aquaculture product in the United States that, with their parent species, are often raised in fresh or near-fresh water and therefore can be exposed to columnaris-causing bacteria. Previous studies have demonstrated that hybrid striped bass are more susceptible to columnaris disease than the maternal white bass parental species. We examined gene expression of gill tissue before infection and at three different time-points after infection with Flavobacterium covae to better understand why there is a difference in resistance. The results of this study indicate that the white bass immune response mechanisms are activated earlier than those of the hybrid striped bass in the presence of this pathogen, which was activated at the same time as mortalities started to be observed in these fish. The immune-related genes identified through this study can be the focus of future research and/or selective breeding efforts to produce a hybrid with greater disease resistance like that of the white bass.

Technical Abstract: Columnaris disease is a prevalent disease in freshwater environments caused by the ubiquitous aquatic bacterium Flavobacterium columnare (covae). Adhesion to the external mucosal surfaces of fishes is the initial stage of infection, and the gills specifically have been identified as both a primary target and release site for this pathogen. Demonstrated here and in previous research, the hybrid striped bass (Morone chrysops x M. saxatilis), a prominent United States aquaculture product, is more susceptible to infection with F. covae than the maternal white bass (M. chrysops) parental species. To further elucidate the mechanisms underlying differences in resistance between these fish we examined gill gene expression profiles using high-throughput RNA sequencing at different time-points after F. covae infection. Patterns of differential gene expression and association with key enrichment terms indicate the effective immune response observed in white bass includes the up-regulation of multiple cytokines (IL-1ß, IL-17C, TNF-a, G-CSF, IL-8, CCL16, CXCL9), hepcidin (HAMP and HAMP2), ribosomal subunit components (e.g., RPL13), and, interestingly, the down-regulation of leptin (LEPA) during initial (1 – 4 h) stages of infection. Conversely, up-regulation of the same genes was not detected in hybrid striped bass until 24 h after infection, indicating a delay in immune response mechanisms that is ultimately ineffective in protecting the host as this was concurrent with the onset of mortality in these fish. Collectively, the presented results include several putative pathways and candidate genes for further investigation toward characterizing immune defense mechanisms underlying the resistance (white bass) and susceptibility (hybrid striped bass) for selective breeding efforts and/or biotechnological intervention.