Light and electron microscope observations on extrasporogonic and sporogonic stages of a myxosporean parasite of the genus Sphaerospora Thelohan, 1892 from Atlantic salmon, Salmo solar L., in Scotland

Abstract. Juvenile Atlantic salmon from a number of freshwater hatcheries in Scotland were found to be infected by a myxosporean parasite of the genus Sphaerospora. Fish first became infected in June by extrasporogonic stages which could be found in the blood and kidney interstitium. These consisted of a primary cell containing one to over one hundred secondary cells. Some secondary cells contained one or two tertiary cells. Sporogony was disporous and occurred later in the kidney tubules. The development of both extrasporogonic and sporogonic stages was studied by light and transmission electron microscopy.