The role of plerocercoids in the biology of Proteocephalus ambloplitis (Cestoda) maturing in smallmouth bass

Plerocercoids of Proteocephalus ambloplitis removed from parenteral sites and the enteron of smallmouth bass, or parenteral sites in other fish from Lake Opeongo, were fed to bass which were either laboratory-reared or captured from the lake and treated with the anthelmintic di-n-butyl tin oxide. The experiments demonstrate that, following growth to plerocercoid I in copepods, plerocercoid II passes through three physiologically distinct levels of development in fish. "Initial" growth may be parenteral in bass or other fish; "middle" growth can be completed only while parenteral in bass; "terminal" growth of plerocercoid II precedes sexual maturation in the gut lumen of bass. Plerocercoids commonly enter the gut of bass by direct entry from parenteral sites in the same fish, and only rarely following ingestion of an infected bass, since cannibalism is rare in Lake Opeongo. Plerocercoids from parenteral sites in fish other than bass are, therefore, an essential reservoir, and most "middle" plerocercoid II ...