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European countries (Scotland, England, Switzerland, Germany, France, among others), Chile and Peru (Sandoval 2017, unpublished report).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European countries (Scotland, England, Switzerland, Germany, France, among others), Chile and Peru (Sandoval 2017, unpublished report).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...

Spawning Rash – Gross Pathology

Rainbow trout, multi-focal granulomatous dermatitis

The bacterium Renibacterium salmoninarum is a small (~ 1.0 μm), intracellular, non-motile diplobacillus, gram +, that is slow growing and a fastidious pathogen. The external gross findings on the skin could be a good example of chronic-active dermal o subdermal lesion associated with R. salmoninarum. “Spawning rash” can be observed in adults, particularly at or around spawning time. Lesions may be largely dermal, often centering round scale-pockets to produce multifocal chronic-active dermatitis. Alternatively the response, mainly in the superficial muscle, may be so severe as...

Caligus Rogercresseyi – Gross Pathology

Atlantic salmon with adult females (C. rogercresseyi). Note the lesions on the skin surface. Note also the paired trailing egg sacs.

Caligus rogercresseyi is a predominant parasitic problem in the salmonid industry in Chile. It mainly affects Atlantic salmon and Rainbow trout. Coho salmon is not considered susceptible due to a well-developed inflammatory response. The life cycle of C. rogercresseyi is composed of eight stages of development, two nauplius stages I and II, an infested copepodite stage, four chalimus stages and an adult stage (young adult and mature adult). The amount of time it takes for a louse to develop depends greatly on the temperature. Under...

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