ABSTRACT
Lymphocystis, a hypertrophic disease of cells primarily in the skin and fins of fish, is the oldest and perhaps best known of all viral diseases of fish. This chapter investigates geographical range, host susceptibility, histopathology, and electron microscopy of lymphocystis and Viral Erythrocytic Necrosis (VEN). Lymphocystis virus is the most widely distributed of the fish viruses. Lymphocystis virus infection is identified by gross clinical signs coupled with the presence of typical enlarged cells containing Feulgen-positive cytoplasmic inclusions in stained histologically sectioned lesions. Lymphocystis is a chronic, benign condition that seldom results in the death of infected fish. VEN is an infection of erythrocytes that affects a wide variety of marine and anadromous fish species. The principle clinical sign of VEN is a severe anemia characterized by pale gills, watery colorless blood, and discolored livers. Pacific herring infected with Erythrocytic Necrosis Virus do show some hemorrhage in the epithelium.
