Some Effects of Two Species of Acanthocephala on the Alimentary Canal of the Largemouth Bass

Abstract

Throughout at least a considerable part of its range in the United States and Canada the largemouth bass Huro salmoides (Lacepede) commonly harbors adults of two species of acanthocephala, Leptorhynchoides thecatus (Linton, 1891) and Neoechinorhynchus cylindratus (Van Cleave, 1913). At Reelfoot Lake, Tennessee, one or both species of these parasites were found in all of twenty-nine bass examined (Venard, 1940). Because of statements in the literature that acanthocephala are harmful to fish, and our failure to discover any description of harm beyond the brief observation that the host's intestine is damaged, pieces of pyloric ceca and small intestine containing these parasites were preserved in formalin during the summer of 1939 for later histological examination. The collection of this material was made possible by a grant from the Reelfoot Lake Biological Station of the Tennessee Academy of Science. The parasitized tissues sectioned were from three bass, 27, 28, and 28.5 cm. in total length. A largemouth bass 39 cm. in total length, which contained no acanthocephala or other helminths when dissected, supplied normal tissues for comparison with parasitized tissues. This specimen was reared in an Ohio fish hatchery and was kindly furnished by Mr. John Pelton of the Ohio Division of Wildlife, Department of Natural Resources. Leptorhynchoides thecatus. As many as 102 individuals were found in a single host. These parasites usually inhabited the pyloric ceca and were rarely found in the small intestine. The following observations are restricted to the ceca. Areas of the ceca which appear not to have been invaded by the parasite present a picture similar to that of normal tissues, from the Ohio fish, except that the mucosa and submucosa are heavily infiltrated with leucocytes. The usual position of a parasite is with its body lying in the lumen of the cecum with its anterior end pressed firmly into the host tissue so that the host tissue surrounds the anterior end of the parasite (Fig. 1). In all our sections of this species the proboscis is retracted and not engaged with the host tissue; this is probably due to retraction of the proboscis while the parasite was being killed with preservative. In the host tissue at the location of the parasite, the mucosa and submucosa are completely disrupted and form a debris containing fragments of the epithelium as isolated clumps of columnar epithelial cells. This cellular debris is heavily infiltrated with erythrocytes and leucocytes. Numerous groups of rod-shaped bacterial cells are also present. The region of disorganized tissue cells extends for several millimeters through the mucosa and submucosa surrounding the anterior end of the parasite. At this point the submucosa can not be recognized as such except in some areas immediately adjacent to the inner circular layer of the tunica muscu