HISTOPATHOLOGICAL EFFECTS OF THE ACANTHOCEPHALAN LEPTORHYNCHOIDES-THECATUS IN THE CECA OF THE GREEN SUNFISH, LEPOMIS-CYANELLUS

Green sunfish (Lepomis cyanellus) possess an alimentary canal that has seven pyloric ceca, some or all of which may be parasitized by the ac anthocephalan Leptorhynchoides thecatus. The microscopic anatomy of ce ca with worms and the microscopic anatomy of ceca without worms in par asitized fish were compared to each other and to that of ceca from unp arasitized fish. Parasites occluded ceca and caused significant disten tion (two-tailed Student's t-test, P < 0.05). Frequently, the probosci s was positioned in the lamina propria, but sometimes attachment was i n the muscularis mucosa. Occasionally, the cecal wall was perforated. Epithelium was destroyed at the site of attachment and cell debris occ urred in the lumen. The abundance of goblet cells in the mucosa of inf ected ceca was significantly greater than in ceca without worms whethe r in parasitized or unparasitized fish. Circular and longitudinal musc le layers in the muscularis mucosa were significantly thicker in paras itized than in unparasitized ceca. Additionally, muscle layers in unpa rasitized ceca of infected fish were significantly thicker than those in uninfected fish, revealing an effect of parasitism more general tha n necrosis at the site of attachment.