ABSTRACT
The terminology of general pathology has been adapted for fish, even though all of the pathological conditions observed in homothermic animals do not occur in fish. This chapter introduces some basic pathologic terms and presents examples of the most common pathological changes that occur in fish. Circulatory disturbances are those abnormalities that reflect injury to the vascular system. The most common types of circulatory disturbances in fish are hemorrhage, edema, hyperemia, congestion, emboli, and telangiectasis. An embolism is an obstruction of some part of the vascular system that interrupts the flow of blood. One of the most common types of fish emboli is the formation of "gas bubbles" in blood vessels caused by a supersaturation of the water by a gas, usually oxygen or nitrogen. Several growth changes may occur in an animal in response to an infection, toxicant, or other irritant.
