Vet Med - Czech, 2026, 71(8):310-321 | DOI: 10.17221/100/2025-VETMED

Susceptibility of different rainbow trout (Oncorhynchus mykiss) genetic lines to infectious diseaseOriginal Paper

I Papezikova ORCID...1,2, V Vaibarova ORCID...3, L Pojezdal ORCID...4, K Matejickova4, J Blahova ORCID...5, J Mendel ORCID...6, E Maresova6, I Mikulikova ORCID...1,2, M Palikova1,2, I Toulova ORCID...1,2
1 Department of Ecology & Diseases of Zoo Animals, Game, Fish and Bees, University of Veterinary Sciences Brno, Faculty of Veterinary Hygiene and Ecology, Brno, Czech Republic
2 Department of Zoology, Fisheries and Hydrobiology, Mendel University in Brno, Brno, Czech Republic
3 Department of Infectious Diseases and Microbiology, Faculty of Veterinary Medicine, University of Veterinary Sciences Brno, Brno, Czech Republic
4 Department of Infectious Diseases and Preventive Medicine, Veterinary Research Institute, Brno, Czech Republic
5 Department of Animal Protection and Welfare & Veterinary Public Health, Faculty of Veterinary Hygiene and Ecology, University of Veterinary Sciences Brno, Brno, Czech Republic
6 Institute of Vertebrate Biology, Czech Academy of Sciences, Brno, Czech Republic

This study assessed the resistance of three rainbow trout (Oncorhynchus mykiss) genetic lines to three pathogens, the bacterium Flavobacterium psychrophilum and the parasites Ichthyophthirius multifiliis and Tetracapsuloides bryosalmonae, by monitoring mortality, immune parameters (leukocyte count and phagocytic activity), and pathogen load. Two of the fish lines tested carried quantitative trait loci associated with resistance to the selected pathogens. Unexpectedly, the line with declared genetic resistance exhibited the highest mortality rate following F. psychrophilum infection, suggesting the influence of additional factors such as differences in strain virulence or interactions between genetic background and environmental conditions. Following I. multifiliis infection, the resistant line initially exhibited a higher parasite load but later achieved more efficient parasite clearance. Overall, the findings suggest that disease resistance in trout is a complex trait influenced by interactions between genotype, pathogen and environment. Consequently, resistant lines must always be tested under specific conditions of the target aquaculture facility before implementation.

Keywords: genetic resistance; Ichthyophthirius multifiliis; proliferative kidney disease; rainbow trout fry syndrome; white spot disease

Received: November 28, 2025; Revised: April 28, 2026; Accepted: April 30, 2026; Published: August 23, 2026  Show citation

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Papezikova I, Vaibarova V, Pojezdal L, Matejickova K, Blahova J, Mendel J, et al.. Susceptibility of different rainbow trout (Oncorhynchus mykiss) genetic lines to infectious disease. Veterinární medicína. 2026;71(8):310-321. doi: 10.17221/100/2025-VETMED.
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