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Diseases of Aquatic Organisms

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DAO 145:111-117 (2021)  -  DOI:

Swim bladder as a primary site of mycobacterial infection in Nothobranchius ‘belly sliders’

I. Dyková1,*,#, J. Žák2,3,#, M. Reichard1,2,4, K. Součková5, O. Slabý5,6, R. Blažek1,2

1Institute of Botany and Zoology, Faculty of Science, Masaryk University, Brno 611 37, Czech Republic
2Institute of Vertebrate Biology, Czech Academy of Sciences, Brno 603 65, Czech Republic
3Department of Zoology, Faculty of Science, Charles University, Viničná 7, Prague 128 43, Czech Republic
4Department of Ecology and Vertebrate Zoology, University of Łódź, Łódź 90-237, Poland
5Central European Institute of Technology, Masaryk University, Brno 625 00, Czech Republic
6Department of Comprehensive Cancer Care, Masaryk Memorial Cancer Institute, Brno 602 00, Czech Republic
*Corresponding author:
#These authors share joint first authorship on this work

ABSTRACT: The swim bladder inflates early after fish hatching via its interconnection with the digestive tract (ductus pneumaticus). This interconnection may serve as a portal to foreign particles, including bacteria, causing deficiencies in primary swim bladder inflation. We histologically examined 134 African annual killifish (genus Nothobranchius) with secondary loss of swim bladder function (‘belly sliders’). We demonstrate that these fish lost the ability of air regulation in their swim bladders likely due to Mycobacterium spp. infection at an individual-specific age. Nearly all examined belly sliders had thickened swim bladder walls, and their swim bladder was filled with material containing mycobacteria, cell debris, young monocytic cells and phagocyting macrophages. Mycobacterial infection was restricted to the swim bladder in juveniles, where mycobacteria likely enter the host through the ductus pneumaticus. Infection in adults was systemic and mycobacteria were present in all examined organs. Presence of mycobacteria in the epithelial lining and submucosal layers of the digestive tract of adults suggests that it may also serve as the entrance site of infection. We suspect 2 sources of Mycobacterium contamination: dietary (with bloodworms) and/or contaminated hatching substrate. These sources of contamination may be eliminated by use of laboratory dry feed and egg disinfection prior to hatching.

KEY WORDS: Abnormal swimming · Model organism · Laboratory-reared killifish · Mycobacterial infection

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Cite this article as: Dyková I, Žák J, Reichard M, Součková K, Slabý O, Blažek R (2021) Swim bladder as a primary site of mycobacterial infection in Nothobranchius ‘belly sliders’. Dis Aquat Org 145:111-117.

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