Tapeworm: Eubothrium salvelini
Volume 3, Issue 6
Updated November 2002
Fig. 1. Tapeworms crawling out of the pyloric caeca of a yearling rainbow trout.
Cestodes can be common in trout and salmon in nature and sometimes in aquaculture. Adult cestodes, like Eubothrium salvelini for example, can be readily identified in salmonids by gross examination of intestines and pyloric caeca. Adult cestodes are cream-white color, come in a variety of widths, and most have long soft flat noodle like bodies that break apart easily into segments.
Fig. 1. Extended scolex (head) of E. salvelini stained red and magnified approximately 100x.
Generally, adult cestodes cause little or no detectable damage in their host, however, some species of cestodes can cause morbidity and mortality in fish, other animals, and humans. Therefore, it is important that tapeworm infected fish be thoroughly cooked before being eaten.
Adult E. salvelini inhabits the intestine and pyloric caeca of many different salmonids (e.g., rainbow trout, brook trout, Pacific salmon, Atlantic salmon, and char). E. salvelini has been found throughout North America. It has a very simple lifecycle. Adults produce millions of eggs in their segmented body (called a strobilia). E. salvelini are hermaphrodites. Each individual proglottid (segment of the strobilia), contains both ovary and teste. The fertilized unoperculated, unembryonated eggs are released from the proglottids into the fish’s intestine and then is excreted into the water with the fish’s feces. Eggs are eaten by freshwater copepods and begin to develop inside the copepod’s body. In turn, the copepod is eaten, directly or indirectly, by a salmonid; attaches to the salmonid’s intestinal wall and begins the metamorphosis into a new adult. E. salvelini can live over 2 years in a trout. In that time span, it can produce millions and millions of eggs.
Heavy infestations of E. salvelini cause reduced growth in trout and salmon, reduced condition factor in trout and salmon, and are aesthetically repulsive and disgusting to many anglers.
Special points of interest:
Fish with certain Cestodes can transmit the parasite to other animals and people.
Many tapeworms have segmented bodies.
E. salvelini infects many species of trout, salmon, and char. It can decrease growth and body condition.
Images were made possible by a grant from the Maine Outdoor Heritage Fund.