Microcirculatory Pathways in the Spleen of the Rainbow Trout Oncorhynchus mykiss

Abstract

Three-dimensional structure of the vascular system of the rainbow trout (Oncorhynchus mykiss (=Salmo gairdneri)) spleen was studied under a scanning electron microscope using mainly corrosion casts. The specialized vessels related to the periarterial lymphatic sheath and lymphatic nodules which are seen in the mammalian spleen were not found in the rainbow trout. A major trunk artery simply gave off arterioles toward the subcapsular region. Termination of arterial capillaries in reticular meshwork, i.e. open circulation, was clearly observed. Arterioles infrequently showed sphincter-like constrictions which probably regulated blood flow through the organ. Reticular meshwork, which appeared in the cast as clusters of granular resin masses, was considered to be an important site for erythrocyte storage. At the subcapsular region the collecting veins, which showed a plate-like structure and lay on the reticular meshwork, gathered into veins which in turn went straight into the inside of the organ and joined a major trunk vein. These veins running from the reticular meshwork to a larger vein were considered to aid the rapid drainage of erythrocytes from the reticular meshwork at times of urgent need, such as during periods of strenuous exercise.