50 NORTHERN FISHES 



ceans are eaten by a tullibee or a whitefish, the parasite is liberated 

 and burrows into the back muscles, forming a large cyst. When the 

 infected tullibee or whitefish is eaten by a northern pike, the parasite 

 is liberated and becomes an adult fastened to the wall of the intestine. 

 This parasite is very abundant in the northern lakes of Minnesota 

 and in Canada, and is responsible for the condemnation of large quan- 

 tities of tullibee by both state and federal authorities as unfit for 

 human food. There are other larvae of related species, one living in the 

 livers of perch and another in the troutperch (the adult forms are 

 found in the walleye) . These parasites are harmless to man. Fortunate- 

 ly the waters of Lake Superior are not highly suited for northern pike, 

 and consequently the very important commercial- crop of the ciscoes 

 and whitefishcs from these waters is not heavily infected. 



Another rather common tapeworm is the bass tapeworm (Proteo- 

 cephalus ambloplites) , which is commonly found in both largemouth 

 and smallmouth bass. This worm lives as an adult in the intestine of 

 bass. The eggs pass into the water and hatch into larvae which enter 

 the body cavity of minute copepods, such as a species of Cyclops. 

 When the Cyclops is eaten by a small bass or certain other fishes, the 

 parasite is liberated in the intestine and undergoes further develop- 

 ment, burrowing into the body cavity where it forms a large larva. 

 At this stage they cause great damage because they tend to destroy 

 the reproductive organs and render the fish sterile. When the infected 

 fish is eaten by a large bass, the parasite completes its development 

 into an adult tapeworm in the intestine. They can cause considerable 

 damage among bass, not only rendering them sterile, but also causing 

 them to become thin and liable to other infections. 



The only known fish parasite capable of infecting man is the broad 

 fish tapeworm (Diphyllohothrimri) originally found in northern Eu- 

 rope. It was probably brought to this country by infected immi- 

 grants. It is a serious menace to man but fortunately is prevalent only 

 in limited localities in the northern states. It has been found in wall- 

 eyes, perch, and northern pike. Human infection occurs only from 

 eating raw or improperly cooked fish — the parasite is killed and 

 rendered harmless when the fish is thoroughly cooked. The adult 

 form of this worm lives in the intestine of man and some carnivores. 

 The eggs pass out with the feces and must enter water to survive. 

 The eggs are then eaten by a species of Cyclops, inside of which they 

 hatch and develop into larval forms. When the Cyclops is eaten by a 

 walleye, northern pike, or perch, the larvae escape and burrow through 

 the intestine into the flesh of the fish, where they encyst and remain 

 until eaten by man or a suitable carnivore. They are then released and 

 mature into adult tapeworms in the intestine. 



There is no doubt that the many kinds of parasites which are so 



