Usually they are cooked, eaten and never 

 noticed, but occasionally they may be seen 

 and may result in unnecessary waste of the 

 fillet or the fish. None has been demon- 

 strated to be harmful to humans. Usually a 

 fish-eating bird or mammal serves as host 

 for the adult worms. 



5. Larval cestodes may localize in the flesh 

 of marine fishes, although this condition 

 seems less frequent than in fresh water. 

 Butterfish of the U. S. east coast fre- 

 quently have tapeworm larvae in small 

 (less than l/Z5-inch) white to yellow cysts 

 in the body muscles. Occasionally enormous 

 numbers of such cysts may be found in 

 individual fish (fig. 21). Other tapeworms 

 may occur as contorted opaque white 

 ribbons in the flesh of fish, often in suf- 

 ficient numbers to require discarding the 

 fish. 



Parasites of the Viscera 



Inhabitants of the visceral mass of fishes 

 are many, and are often apparent when fish 

 are dressed. Adult worms--cestodes, tre- 

 matodes, nematodes, and acanthocephala-- 

 usually occupy the digestive tract, while 

 larval stages of members of these groups 

 may be foiind, usually encysted, in the gut 

 wall, the liver, or the supporting mem- 

 branes. In addition to worm parasites, 

 there may be protozoan and fungus infec- 

 tions. 



1. Protozoa may occur in nodules or cysts 

 on and in the viscera of fish. These are 

 actually masses of thousands of spores, 

 much like the nodules or cysts in the flesh. 

 Conspicuous in this respect are such forms 

 as Glugea hertwigi, a nnicrosporidian that pro- 

 duces white cysts in the viscera of eastern 

 smelt (fig. 22). This parasite nnay occa- 

 sionally be sufficiently abundant to interfere 

 with reproduction. It varies in abundance 

 geographically, and may occur in over one- 

 quarter of all fish sampled in particular 

 areas. 



2. Fungus infections and resulting involve- 

 ment of the viscera are found in such 

 marine fishes as the Atlantic herring, 

 mackerel, and flounder. A fungus disease 



Figure 19.--Adult herring infected with fungus. Top--skin has 

 been sliced away to show normal muscle. Lower --shows ad- 

 vanced decay of muscles. 



Figure 21.--Larval tapeworms in the flesh of bunerfish. 



Figure 20,- -Smelt with codworms encysted in flesh. 



Figure 22.--Visceral cysts of the microsporidianC/ugea hertwigi 

 in a smelt. 



14 



