Home Disease Challenges Winter Ulcer

Winter Ulcer

Moritella viscosa

Animal model: Atlantic salmon

Source of CAT isolates:  

Applications: Vaccines, functional feeds, repellents, physical barriers, environmental treatments, system modification, immersion and in feed treatments, benchmarking commercial treatments, genetic selection/ phenotyping

Type of model: Immersion, Intraperitoneal (IP)

Clinical Signs of Disease in our Model: Cutaneous lesions which develop to sub cutaneous ulcerative lesions with skeletal muscle exposed, typically large and on a single flank

Challenge conditions: 25-35ppt, 3-12C

Other end points: Semi-quantitative pathological scoring, periodic sampling

Starting Fish Size: 50 g - 2 kg


Atlantic salmon exhibiting classical manifestation of winter ulcer disease, with a large ulcerative lesion on the right flank.


The bacterium Moritella viscosa is the autological agent of winter ulcer disease. Typically, infection and associated pathogenesis are of the highest risk in colder water temperatures (<8°C), though the pathogen is often isolated at warmer temperatures as well. The disease has a classical presentation of large ulcerative skin lesion(s) which are subcutaneous which can cause the skeletal muscle to be exposed. Field outbreaks can result in high mortality, though most often the disease presentation is chronic leading to economic and animal welfare concerns. Chronically affected animals may be moribund, show reduced growth, and are of poor harvest quality. The disease challenge models developed at CAT have been designed to simulate farm outbreaks and can be manipulated to cause acute or chronic pathogenesis and mortality. The model is frequently used to test the efficacy of several novel feed, vaccine, and other technologies, as well as to benchmark existing commercial treatments.

Representative mortality curves when fish are challenged with M. viscosa under conditions to elicit low, medium, or high mortality in control groups.

We can customize existing models and develop tailored solutions based on your needs