Saprolegnia Infection in Fish – Gross Pathology and Histopathology

Saprolegnia often presents as a secondary infection that is diagnosed by the appearance of white or grey cotton-like tufts that, when out of water, have a somewhat mucoid appearance. Typical disease signs are visible circular or crescent-shaped, cotton-wool like, white or grey patches of filamentous mycelia on the fish skin. The lesions appear mainly around the head and the caudal, adipose and anal fins. Lesions may spread over the body until adjacent lesions coalesce.

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Tenacibaculosis Histopathology

Tenacibaculosis is a serious bacterial disease affecting a great variety of marine fish, especially those species under culture conditions, causing necrotic lesions on the body. Gross pathological signs vary according to the species and age of fish involved. Characteristic clinical signs are ulcerative skin lesions, mouth erosion and ulceration, and fraying of fins and tail. In general, it is mainly a superficial infection, but some isolates are highly toxigenic, and systemic disease can therefore result, involving different internal organs. Several species of Tenacibaculum can be...

Tenacibaculosis in Fish – Gross Pathology

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...

Strawberry Disease in Rainbow Trout– Histopathology

Figure 1. Strawberry disease in rainbow trout in freshwater showing loss of scales, and accompanying haemorrhage into the scale pockets. Note the severity of the dermal inflammation, which is mostly mononuclear, and largely avoids the epidermis.

Strawberry Disease (SD) is a chronic, nonlethal skin condition that affects Rainbow Trout (Oncorhynchus mykiss) in the United States, several European countries (Scotland, England, Switzerland, Germany, France, among others), Chile and Peru (Sandoval 2017, unpublished report). In Europe it is also known as Red Mark Syndrome (RMS) or Cold-Water Strawberry Disease (CWSD). SD is characterized by raised, sometimes bright red inflammatory lesions that can occur in almost any size of fish bigger than fingerlings, but usually in growing or market-sized fish. The disease presents as...

Strawberry Disease in Rainbow trout – Gross Pathology

Rainbow trout with SD, showing characteristic bright-red lesions on the skin, and scale loss.

Strawberry Disease (SD) is a chronic, nonlethal skin condition that affects Rainbow Trout (Oncorhynchus mykiss) in the United States, several European countries (Scotland, England, Switzerland, Germany, France, among others), Chile and Peru (Sandoval 2017, unpublished report). In Europe it is also known as Red Mark Syndrome (RMS) or Cold-Water Strawberry Disease. The severity of the skin lesions suggests a hypersensitivity response, but hypersensitivity to what?  Affected fish respond well to immune suppressors including corticosteroids, but also to a wide range of antibiotic treatments, suggesting that...

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