Proteocephalus spp

From Fish
Heavily infected ayu
Proteocephalus spp from ayu
Largemouth bass splenic mesentary infested by bass tapeworm plerocercoids

The Bass Tapeworm (Proteocephalus ambloplitis) is a member of a large group of cestode parasites that infect many different species. Smallmouth bass (Micropterus dolomieu) and Largemouth bass (M. salmoides) in some Maine lakes, rivers, and ponds are infected with a Cestode parasite. These parasites can be a serious health problem for bass, perch, and other freshwater fishes.


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[1].

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[2].

Clinical signs

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[3].

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 its 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.


Praziquantel is the drug of choice for treatment of P. ambloplitis in fish.


  1. Ogawa, K. (2004) Metazoan diseases. Infectious and parasitic diseases of fish and shellfish. (ed. by Wakabayashi, H. and K. Muroga), Koseisha Koseikaku, pp:.381-405
  2. Maine Department of Inland fisheries and Wildlife
  3. Takahashi, S. (1973) Studies on Proteocephalus plecoglossi Yamaguti parasitizing ayu, Plecoglossus altivelis. I Bull Shiga Pref Fish Exp Station 24:63-82