Which of the following is a symptom of Epizootic Ulcerative Syndrome?

Epizootic Ulcerative Syndrome (EUS), also known as "Red Spot Disease," is characterized by significant clinical signs that primarily include the development of red spots and ulcerative lesions on affected fish. These lesions are often due to a specific fungus associated with the disease, which generally causes severe skin and tissue damage. The presence of ulcerative lesions is a hallmark symptom, indicating the disease's impact on the fish’s integumentary system.

While white spots on the skin, loss of scales, and fin deterioration could suggest various diseases or conditions, they do not specifically capture the defining features of EUS. The characteristic red spots and ulcerations directly indicate tissue damage and infection, making them the most defining symptoms of this syndrome. Thus, identifying these signs is crucial for diagnosing EUS and distinguishing it from other aquatic diseases.