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The Bass Tapeworm (Proteocephalus ambloplitis)

Volume 1, Issue 1
September 1999
Updated November 2002

Smallmouth bass (Micropterus dolomieu) and Largemouth bass (M. salmoides) in some Maine lakes, rivers, and ponds are infected with a Cestode parasite. The unsightly parasite is of no human health concern, but can be a serious health problem for bass, perch, and other freshwater fishes. The Bass Tapeworm (Proteocephalus ambloplitis) is a member of a large group of segmented parasites that infect many different species. The adult P. ambloplitis tapeworm infests the intestine of the black basses. Here it attaches to the inner intestinal wall with four suckers called “scolexes.” A single worm is both male and female. The adult worm sucks nutrients from the host bass using the nutrients to produce egg filled body segments called “proglottids.” These egg filled proglottids are released from the adult worm and pass with the fish’s feces into the water. Once in the water the proglottid hatches and the eggs are dispersed into the water. The eggs are eaten by a variety of crustacean organisms. Within the body of the crustacean, the egg hatches and develops into blunt shaped larvae, called a “proceroid.” When the crustacean is eaten by almost any fish, the proceroid larvae bores through the wall of the fish’s digestive tract and invades it’s abdominal organs. It is during this migration and the tapeworms transformation from a procercoid to a plerocercoid that the gross internal abdominal damage is done to the host fish. Small mouth bass infected with plerocercoids typically have liver , spleen, and reproductive organs damaged. Fish with chronic infections also have scar tissue adhesions. Their internal organs grossly appear as a single mass. Many times the mass of internal organs is firmly attached to the fish’s inside body wall. These fish have pot bellies, are often sterile, and have stunted growth. This is the stage of bass tapeworm that is most often noticed by fishermen and makes the bass unappealing for food even though the eating quality of the fish is not affected and there is no human danger. The plerocercoid infected fish must then be eaten by a smallmouth or largemouth bass in order to complete the bass tapeworm’s lifecycle. During digestion of the small fish in the larger fish’s stomach and intestine, the plerocercoid transforms into an adult P. ambloplitis, embeds it’s scolexes into the intestinal wall of the host, and begins making egg filled proglottids to be released into the water with the host fish’s feces. A small mouth bass can be infected with more than one tapeworm and more than one life stage simultaneously.

Bass tapeworm

Control Measures


Don’t transport bass from one water to another without an IF& W stocking permit.

Don’t release live baitfish into water.

Don’t dispose of fish entrails into water.

Special points of interest:


· Adult tapeworms live in smallmouth bass intestine. Here they produce eggs.

· Eggs are eaten by crustaceans and develop into procercoid.

· Crustaceans are eaten by fish and pass the immature tapeworm to the fish.

· A smallmouth bass must eat the infected fish to complete the tapeworm’s lifecycle.

Mesenteric adhesions and scaring


Figure 2. Ceolomic cavity of largemouth bass scarred by a chronic bass tapeworm infestation. Adhesions caused by the body’s reaction to migrating larvae can make the fish sterile.

splenic mesentary


Figure 3. Largemouth bass splenic mesentary infested by bass tapeworm plerocercoids.

Images in this document were made possible in part by a grant from the Maine Outdoor Heritage Fund.