Gastric Evacuation and Movement of Materials through the Alimentary Canal of Green Sunfish

Abstract

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 region of sequestered nutrients. Adults of the acanthocephalan parasite Leptorhynchoides thecatus are restricted to the seven pyloric ceca in green sunfish Lepomis cyanellus. Gastrointestinal motility of green sunfish was investigated to determine if ceca provide a sheltered or nutrient-sequestering region for L. thecatus. Gastric evacuation and the movement of materials through the alimentary canal were determined by monitoring the movement of meals containing dye, accomplished by inserting gelatin capsules containing dye into the body cavity of American cockroaches Periplaneta americana, which were fed to the sunfish, and recording observations at various time intervals postfeeding. Gastric evacuation occurred 24–32 h postfeeding. Approximately 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 later times. By 30 min, small amounts of food were observed in the ceca and proximal intestine. By 1 h, and at all subsequent times until voidance of the meal, food was present in the ceca and intestine. Time required for complete voidance of a meal from the alimentary canal ranged from 41 to more than 61 h at 21°C. Food traveled sequentially through the ceca and intestine and was not sequestered in the ceca. Upon gastric evacuation all food 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 intestine. At all postfeeding sampling times, more material was in the ceca than 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 green sunfish, the ceca do not serve as a nutrient sequestering region. Furthermore, the relatively large amount of food passing through the ceca suggests peristaltic capabilities similar to other regions of the enteric system; thus, ceca seem unlikely to provide a sheltered region for helminths.