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Swim bladder as a primary site of mycobacterial infection in Nothobranchius 'belly sliders'
1Institute of Botany and Zoology, Faculty of Science, Masaryk University, Brno 611 37, Czech Republic.
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.
Insights
African killifish with secondary swim bladder loss (
Area of Science:
- Ichthyology
- Aquatic Animal Health
- Microbiology
Background:
- The swim bladder inflates early after fish hatching via its connection to the digestive tract (ductus pneumaticus).
- This connection can allow foreign particles, including bacteria, to enter, potentially causing swim bladder inflation deficiencies.
- Secondary loss of swim bladder function, termed 'belly sliders', is observed in some fish species.
Purpose of the Study:
- To investigate the cause of secondary swim bladder loss in African annual killifish (genus Nothobranchius).
- To determine the role of bacterial infection in the development of 'belly slider' phenotype.
- To identify potential sources of contamination and suggest preventative measures.
Main Methods:
- Histological examination of 134 African annual killifish exhibiting secondary swim bladder loss.
- Microscopic analysis to identify the presence and type of bacteria within swim bladder tissues and other organs.
- Assessment of swim bladder wall thickness and internal contents.
Main Results:
- Mycobacterium spp. infection was identified as the likely cause of secondary swim bladder loss in Nothobranchius killifish.
- Infected fish exhibited thickened swim bladder walls filled with mycobacteria, cellular debris, and immune cells.
- Infection pathway involved the ductus pneumaticus in juveniles and became systemic in adults, potentially entering through the digestive tract.
Conclusions:
- Mycobacterium infection leads to secondary swim bladder loss in African killifish.
- Potential contamination sources include diet (bloodworms) and hatching substrate.
- Preventative measures involve using laboratory dry feed and disinfecting eggs before hatching.
