Tenacibaculosis in Fish – Gross Pathology

Gills and Pseudobranchs, Multisystem, Skin
by Carlos Sandoval
Figure 1. Rainbow trout displaying tail and peduncle lesions.

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. dicentrarchi, T. finnmarkense, and T. maritimum.   These bacteria are all Gram-negative and filamentous.  In marine fish, the most common isolate is T. maritimum. There is variation in the external pathological signs of the disease, depending on the species and age of the fish involved. Different names have been used for this usually ulcerative dermatitis; they include salt water columnaris...

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Gas Bubble Disease

Multisystem
by Hugh Ferguson
Figure 1. Rainbow trout with several gas bubbles in the anterior chamber. Note the haemorrhage both dorsally and ventrally, the latter “coning” through the ventral iris pore

Gas bubble disease (GBD) is the fish equivalent of the “bends” in human scuba divers. It is the result of gas coming out of solution in the bloodstream, thereby leading to the formation of emboli, especially in smaller blood vessels, including rete. Thus, lesions are common in gills, and the choroid gland of the eye. In water that is supersaturated, fish equilibriate with that supersaturated gas, just as human scuba divers equilibriate with gas at high pressures. It is not known precisely what prompts the...

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Short operculum – Gross Pathology

Gills and Pseudobranchs
by Carlos Sandoval
Figure 1. Severe opercular erosion in farmed rainbow trout.

Bone deformities occur regularly in fish farms around the world. The operculum is one of the earliest craniofacial bones to form embryologically and is subject to a range of developmental and acquired abnormalities. Opercular shortening is one of the most prevalent diseases in larval and juvenile salmonids (and other species), sometimes affecting up to 80% of fish in a population. In those species that rely on the operculum to help move water over the gills, loss of efficiency in this part of the pumping mechanism...

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Flavobacterium psychrophilum in salmonids – Gross Pathology

Multisystem
by Hugh Ferguson
Figure 2. F. psychrophilum infection in rainbow trout. Note the classical “peduncle disease” with necrosis and darkening of tissues distal to the anal fin.

Flavobacterium psychrophilum is a ubiquitous Gram-negative filamentous and yellow-pigmented bacterium, and as the name suggests, it thrives in cooler water temperatures, causing disease in freshwater fish at 4-12°C. It likes connective tissues, especially those in younger fish in which it causes diseases such as bacterial cold-water disease (BCWD or peduncle disease) and rainbow trout fry syndrome (RTFS). As fish get older and the proportions/chemistry/locations of connective tissue change, the types of lesions also change. F. psychrophilum is responsible for significant economic losses in salmonid aquaculture...

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Blue sac disease (BSD) – Gross Pathology

Yolk-sac
by Carlos Sandoval
Blue sac disease in Atlantic salmon yolk-sac fry. Note a gill haemorrhage.

Blue-sac disease (BSD) or dropsy (hydrocoele embryonalis) is an abnormal condition that affects the egg and sac fry stages, typically of trout and salmon, but also of other freshwater fishes whose young emerge with a relatively large yolk sac.  It is characterized by abnormal accumulation of fluid with bluish tint between the yolk-sac and the outer membranes of the fry. It may also involve the pericardium and lymphatic spaces. BSD can be observed shortly after hatching and become more apparent within a few days. Blue-sac...

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