Ecology of the Trematode, Clinostomum marginatum, and Its Hosts in Eastern Kansas

Much of the fishing in eastern Kansas is done in farm ponds and small reservoirs; occasionally, the State Biological Survey of Kansas receives inquiries from fisherman about "wormy" fish, usually with reference to farm ponds. The infections most often noted by anglers ate metacercariae of Clinostomum marginatum (Rudolphi), a trematode (flatworm), commonly called the yellow grub. Although the parasite is harmless to man and there is little evidence that the yellow grub seriously affects the health of fishes, many fishermen discard infected fish because they are unattractive for human consumption. The life cycle of the yellow grub, as described by Hunter and Hunter (1934), is typical of trematodes for which fishes serve as intermediate hosts. A ciliated larva (miracidium) hatches from the egg in water, enters a snail of the genus Helisoma (first intermediate host) and, shedding its cilia, changes into a sporocyst. Rediae are produced parthenogenetically from germ cells within the sporocyst. Similarly, reproductive cells within the redia give rise either to larvae known as cercariae, or to daughter rediae which then produce cercariae. Cercariae leave the snail and, swimming by means of forked tails, come into contact with and penetrate fishes (second intermediate hosts). On entering the fish, cercariae shed their tails and secrete cysts, becoming metacercariae ("yellow grub" stage objectionable to anglers). These become adults on ingestion of the fish by the definitive host (a bird, usually a heron). Soon after reaching the stomach of the bird, the cysts surrounding the metacercariae are digested by enzymes in the stomach of the bird. The metacercariae migrate up the esophagus where the worms attach to the inner lining of the buccal cavity, upper esophagus, or trachea and become sexually mature adults in four to six hours. As the heron feeds, eggs are expelled into the water and the cycle is completed. In view of the possible significance of yellow grub infections in future fisheries management in Kansas, this investigation was undertaken to ascertain: (1) the extent of yellow grub infections in a series of farm ponds of unknown degree of infection, and (2) ecological factors associated with the occurrence and degree of infection in these ponds, and (3)