Distribution of ferric iron in juveniles of the lamprey Petromyzon marinus L.

Sites of iron deposition in tissues and organs of juvenile lampreys (Petromyzon marinus L.) were compared in animals feeding on Salmo gairdneri and nonfeeding individuals using light microscopy and the Prussian blue stain. The liver and adipose tissue are the primary sites of iron storage in all animals and they contain slightly higher concentrations of iron in nonfeeding individuals. Substantial amounts of iron are present in several regions of fibrous connective tissue, in cartilage, and in the meninges. The presence of iron-positive granules and globules in both the mucous cells of the epithelium and the lumen of the posterior intestine suggests that this region of the intestine is a site where excess iron is eliminated. Mucous cells of the dorsal epidermis and the gills probably also release excess iron during mucous secretion. Heavy deposits of iron in subepithelial macrophages and light iron staining of the epithelium of the anterior intestine during times of active feeding imply that the epithelium of this part of the intestine is involved in absorption and that macrophages concentrate the iron. The extensive distribution and heavy concentration of iron in this obligate sanguivore may necessitate the existence of an efficient mechanism for controlling iron intake during feeding.