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

Abstract

Pyloric caeca are present in some species of fish and serve as a habitat for many helminth parasites. Physiological and biochemical attributes of luminal contents of the caeca and proximal intestine of green sunfish, Lepomis cyanellus, were compared to determine factors that could account for localization of Leptorhynchoides thecatus (Acanthocephala) in caeca after initial establishment in caeca and anterior portion of the intestine. Caecal protein concentrations were significantly higher. The anterior intestine exhibited significantly higher levels of proteolytic activity; however, caeca exhibited higher levels of aminopeptidase activity. The pH of caeca was significantly higher than that of the proximal portion of the intestine. Caeca contained greater total amounts of materials, and therefore contained greater total amounts of proteins, free amino acids, lipids, carbohydrates, and bile salts. A significant time–place interaction was detected regarding total free amino acids, suggesting that enzymatic activity in the caeca was responsible for increased amounts of intestinal amino acids. Physiological factors that might influence microhabitat specificity of L. thecatus include inadequate levels of intestinal protein, different levels of proteolytic activity (perhaps resulting from differences in pH), such as aminopeptidase activity, and lack of sufficient quantities of anterior intestinal nutrients to sustain worms. These results demonstrate subtle spatial and temporal complexities intrinsic to the environment of helminths inhabiting the teleost enteric system.