Ultrastructural observations on the sexual stages and oocyst formation inEimeria laureleus (Protozoa, Coccidia) of perch,Perca flavescens, from Lake Sasajewun, Ontario

Abstract

Ultrastructural features of the sexual stages and oocyst formation ofEimeria laureleus are described from the intestinal epithelium of naturally infected perch (Perca flavescens). Daughter nuclei in maturing microgamonts became aligned in the peripheral cytoplasm opposite thickenings in the limiting membrane. A pair of centrioles, originally arranged at right angles, transformed into basal bodies from which two axonemes arose during the formation of microgametes. Macrogamonts were bound by a trilaminar limiting membrane and were closely invested by the membrane of the parasitophorous vacuole. Maturing macrogamonts had a central nucleus, granular endoplasmic reticulum, amylopectin granules, lipid and peripherally arranged dense, membrane-bound inclusions and mitochondria. Spherical zygotes underwent two divisions to form the sporoblasts, each of which contained, in addition to the above mentioned organelles and inclusions, a large dense refractile body. Each of the four sporocysts contained two residual bodies and closely spaced tubular structures. Slender extensions arose from the sporocyst walls which were about 50 nm thick and were composed of a narrow lucent outer zone and a thicker inner, denser zone which is often striated. The sporocysts were bivalved and joined by a continuous suture. The oocyst boundary was multilaminate and appeared to be composed of components of both the parasite and host cell.