Number, location and severity of coronary arterial changes in steelhead trout (Salmo gairdnerii).

Steelhead trout (Salmo gairdnerii) were taken at three stages of sexual maturity to study their coronary arteries for arteriosclerotic lesions. At least 18 sections from the glutaraldehyde- and osmium-fixed arteries were obtained from each fish. Fish in the middle of the spawning migration and sexually mature fish at the spawning ground had lesions in about 20% of the arterial sections. These consisted of focal proliferations of smooth muscle cells projecting into the lumen through the broken elastic lamina with an intact endothelium around them. Sexually mature fish with patches of fungus on their head and back had twice as high a percentage of arterial sections with lesions as the first two groups of fish. Sexually immature fish were not studied. The lesions occurred approximately equally in all sizes of coronary arteries except for very small arteries. All lesions but one were focal; that lesion involved a third of the intima and the media. The lesions have no elastic lamina below the endothelium and seem to have no lipid.