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...