Figure 1. Rainbow trout displaying tail and peduncle lesions.

Tenacibaculosis in Fish – Gross Pathology

Tenacibaculosis is primarily a skin infection causing ulcerative dermatitis in a range of commercially important species worldwide. Three species belonging to the genus Tenacibaculum have been associated with the disease: T. dicentrarchiT. finnmarkense, and T. maritimum.  

Figure 1. Rainbow trout displaying tail and peduncle lesions.
Figure 1. Rainbow trout displaying tail and peduncle lesions.

These bacteria are all Gram-negative and filamentous.  In marine fish, the most common isolate is T. maritimum.

Figure 2. Coho salmon displaying tail and peduncle lesions, caused by T. dicentrarchi.
Figure 2. Coho salmon displaying tail and peduncle lesions, caused by T. dicentrarchi.











There is variation in the external pathological signs of the disease, depending on the species and age of the fish involved.

Figure 3. Tenacibaculosis in red conger eel with ulcerative lesions on face, mouth and head.
Figure 3. Tenacibaculosis in red conger eel with ulcerative lesions on face, mouth and head.



Different names have been used for this usually ulcerative dermatitis; they include salt water columnaris disease, gliding bacterial disease of sea fish, bacterial stomatitis, eroded mouth syndrome, and black patch necrosis (BPN).

Figure 4. Red conger eel. This is the same fish in figure3 from another point of view. Note the loss of tissue integrity from the mouth and face.
Figure 4. Red conger eel. This is the same fish in figure3 from another point of view. Note the loss of tissue integrity from the mouth and face.










Affected fish may have an eroded mouth, frayed fins, tail rot, or characteristic dark necrotic patches on the skin surface.

Figure 5. Atlantic salmon with Tenacibaculosis. Note the ulcerative lesions on the peduncle (Picture courtesy of Pedro Ilardi)
Figure 5. Atlantic salmon with Tenacibaculosis. Note the ulcerative lesions on the peduncle (Picture courtesy of Pedro Ilardi)





Skin lesions are often haemorrhagic and surrounded by a wider zone of darkened dermis, representing activated dermal melanocytes, or by a zone of yellow, representing the yellow-pigmented bacteria themselves.

Figure 6. Rainbow trout in seawater with Tenacibaculosis. Note the severe ulcerative lesions on the head.
Figure 6. Rainbow trout in seawater with Tenacibaculosis. Note the severe ulcerative lesions on the head.






Epidermal erosion with attached bacterial mats often progresses to low level  inflammation in scale pockets, with oedema, and often scale loss, followed by full-thickness epidermal erosion and haemorrhagic ulceration; these latter lesions can have a prominent white rim of exposed collagen.

Figure 7. Chinook salmon with Tenacibaculum infection. Note the ulcerative lesions on the flank with muscle exposure and the presence of frayed fins (Picture courtesy of César López).
Figure 7. Chinook salmon with Tenacibaculum infection. Note the ulcerative lesions on the flank with muscle exposure and the presence of frayed fins (Picture courtesy of César López).








Lesions on the head often involve the mouth and include focal yellow bacterial mats on the palate and base of the teeth.

Figure 8. Chinook salmon with severe tail rot caused Tenacibaculum infection (SW). This is the same fish as figure 7 (Picture courtesy of César López).
Figure 8. Chinook salmon with severe tail rot caused Tenacibaculum infection (SW). This is the same fish as figure 7 (Picture courtesy of César López).









The lesions range from small and hardly visible to multiple and plaque-like, with erosion of the upper and/or lower jaw in severe cases.

Figure 9: Atlantic salmon with focal necrotizing stomatitis caused by T. maritimum. Note the distinctive plaques of yellow pigmentation often present on the edges of these lesions.
Figure 9: Atlantic salmon with focal necrotizing stomatitis caused by T. maritimum. Note the distinctive plaques of yellow pigmentation often present on the edges of these lesions.





Even small lesions can be significant, as these bacteria are highly toxigenic and can have profound systemic consequences.

Figure 10: Severe ulcerative dermatitis in farmed halibut associated with filamentous bacteria, likely T. maritimum. The lesion is bright yellow, due to the bacteria.

Figure 10: Severe ulcerative dermatitis in farmed halibut associated with filamentous bacteria, likely T. maritimum. The lesion is bright yellow, due to the bacteria.











In severe outbreaks, erosion down to the skull, with exposure of bone may be found. Internal lesions include ascites, paleness and swelling of liver, spleen and stomach. The presentation can suggest toxaemia.

Figure 11: Severe full-thickness ulcerative dermatitis in farmed halibut associated with filamentous bacteria, likely T. maritimum. The lesion is rimmed by bright yellow, due to the bacteria.
Figure 11: Severe full-thickness ulcerative dermatitis in farmed halibut associated with filamentous bacteria, likely T. maritimum. The lesion is rimmed by bright yellow, due to the bacteria.





Lesions in gills can be found anywhere, including the gill arches, but they are generally restricted to lamellae and filaments and include severe necrosis and even infarction.

Figure 12: Severe ulcerative dermatitis in an aquarium-housed seabass associated with filamentous bacteria, likely Tenacibaculum sp.
Figure 12: Severe ulcerative dermatitis in an aquarium-housed seabass associated with filamentous bacteria, likely Tenacibaculum sp.










Some jellyfish have been shown to carry the bacteria and it has been suggested that they may act as reservoirs of infection and even vectors, especially those species of jellyfish small enough to pass through the mesh of nets, and hence also be present in the water passing over the gills.

Figure 13: Severe chronic ulcerative dermatitis in Atlantic salmon caused by T. maritimum. Note the prominent white rim of collagen.
Figure 13: Severe chronic ulcerative dermatitis in Atlantic salmon caused by T. maritimum. Note the prominent white rim of collagen.

The precise relationship between the bacteria and the jellyfish is unclear; are they a pathogen of the jellyfish, or are they present in a symbiotic or commensal capacity?

Figure 14: Extensive plaque-like dermatitis in Atlantic salmon; the yellow colour is exclusively due to the presence of large mats of yellow-pigmented and filamentous bacteria.
Figure 14: Extensive plaque-like dermatitis in Atlantic salmon; the yellow colour is exclusively due to the presence of large mats of yellow-pigmented and filamentous bacteria.

















REFERENCES

  • Avendaño‐Herrera, R., Irgang, R., Sandoval, C., Moreno‐Lira, P., Houel, A., Duchaud, E., … & Ilardi, P. (2016). Isolation, characterization and virulence potential of Tenacibaculum dicentrarchi in salmonid cultures in Chile. Transboundary and emerging diseases63(2), 121-126.
  • Avendaño-Herrera, R., Toranzo, A. E., & Magariños, B. (2006). Tenacibaculosis infection in marine fish caused by Tenacibaculum maritimum: a review. Diseases of aquatic organisms71(3), 255-266.
  • Ferguson, H. W., Christian, M. D., Hay, S., Nicolson, J., Sutherland, D., & Crumlish, M. (2010). Jellyfish as vectors of bacterial disease for farmed salmon (Salmo salar). Journal of veterinary diagnostic investigation, 22(3), 376-382.
  • Gourzioti, E., Kolygas, M. N., Athanassopoulou, F., & Babili, V. (2016). Tenacibaculosis in aquaculture farmed marine fish. Journal of the Hellenic Veterinary Medical Society67(1), 21-32.
  • Grothusen, H., Castillo, A., Henríquez, P., Navas, E., Bohle, H., Araya, C., … & Mancilla, M. (2016). First complete genome sequence of Tenacibaculum dicentrarchi, an emerging bacterial pathogen of salmonids. Genome Announc.4(1), e01756-15.
  • Haridy, M., Hasheim, M., El-Galil, M. A., Sakai, H., & Yanai, T. (2015). Pathological Findings of Tenacibaculum maritimus Infection in Black Damselfish, Neoglyphieodon melas and Picasso Triggerfish, Rhinecanthus assasi in Red Sea, Egypt. Veterinary Science & Technology6(2), 1.
  • Roberts, Ronald J. (2012). Fish Pathology. Hoboken, NJ: Wiley-Blackwell

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