Physiological attributes of the pyloric caeca and anterior intestine of green sunfish (Lepomis cyanellus) potentially influencing microhabitat specificity of Leptorhynchoides thecatus (Acanthocephala)

Pyloric caeca are present in some species of fish and serve as a habitat fo r many helminth parasites. Physiological and biochemical attributes of lumi nal contents of the caeca and proximal intestine of green sunfish, Lepomis cyanellus, were compared to determine factors that could account for locali zation of Leptorhynchoides thecatus (Acanthocephala) in caeca after initial establishment in caeca and anterior portion of the intestine. Caecal prote in concentrations were significantly higher. The anterior intestine exhibit ed significantly higher levels of proteolytic activity; however, caeca exhi bited higher levels of aminopeptidase activity. The pH of caeca was signifi cantly higher than that of the proximal portion of the intestine. Caeca con tained greater total amounts of materials, and therefore contained greater total amounts of proteins, free amino acids, lipids, carbohydrates; and bil e salts. A significant time-place interaction was detected regarding total free amino acids, suggesting that enzymatic activity in the caeca was respo nsible for increased amounts of intestinal amino acids. Physiological facto rs that might influence microhabitat specificity of L. thecatus include ina dequate levels of intestinal protein, different levels of proteolytic activ ity (perhaps resulting from differences in pH), such as aminopeptidase acti vity, and lack of sufficient quantities of anterior intestinal nutrients to sustain worms. These results demonstrate subtle spatial and temporal compl exities intrinsic to the environment of helminths inhabiting the teleost en teric system. (C) 1999 Elsevier Science Inc. All rights reserved.