Gastric evacuation and movement of materials through the alimentary canal of green sunfish

Pyloric ceca, the function of which is unclear, often harbor large numbers of helminths. Ceca may provide a sheltered region for worms or provide a re gion of sequestered nutrients. Adults of the acanthocephalan parasite lepto rhynchoides thecatus are restricted to the seven pyloric ceca in green sunf ish Lepomis cyanellus. Gastrointestinal motility of green sunfish was inves tigated to determine if ceca provide a sheltered or nutrient-sequestering r egion for L. thecatus. Gastric evacuation and the movement of materials thr ough the alimentary canal were determined by monitoring the movement of mea ls containing dye, accomplished by inserting gelatin capsules containing dy e into the body cavity of American cockroaches Periplaneta americana, which were fed to the sunfish, and recording observations at various time interv als postfeeding. Gastric evacuation occurred 24-32 h postfeeding. Approxima tely 25% of the stomach contents were evacuated by 4 h and 50% were by 12 h . Rate of gastric evacuation was higher at 2 and 4 h postfeeding than at la ter times. By 30 min, small amounts of food were observed in the ceca and p roximal intestine. By 1 h, and at all subsequent times until voidance of th e meal, food was present in the ceca and intestine. Time required for compl ete voidance of a meal from the alimentary canal ranged from 41 to more tha n 61 h at 21 degrees C. Food traveled sequentially through the ceca and int estine and was not sequestered in the ceca. Upon gastric evacuation all foo ds was voided from the ceca. Starved fish had significantly more endogenous material in the ceca than in the anterior third or middle third of the int estine. At all postfeeding sampling times more material was in the ceca tha n in the anterior intestine. Food, after leaving the ceca, appeared to move rapidly through the anterior intestine before slowing and accumulating in the middle intestine. Although food enters ceca in substantial amounts in g reen sunfish, the ceca do not sere as a nutrient sequestering region. Furth ermore, the relatively large amount of food passing through the ceca sugges ts peristaltic capabilities similar to other regions of the enteric system; thus, ceca seem unlikely to provide a sheltered region for helminths.