of marine fishes, caused hy Ichthyosporidium 

 hoferi, has received some attention in recent 

 years, especially in North America, where 

 it has periodically assunned epidemic pro- 

 portions in the Atlantic herring. Visceral 

 symptoms often include extensive white 

 nodules on and in the heart, liver, gonads, 

 and mesenteries (fig. 23). 



3. Adult trematodes are connmon, but their 

 small size and location within the gut make 

 them inconspicuous. Occasionally hundreds 

 or even thousands of these small adult 

 worms may be found in the digestive tract 

 of a single fish. They are usually less 

 than 1/4 inch long, opaque white, with a 

 brownish patch of eggs near the center or 

 posterior part of the body. 



4. Larval nematodes may localize in the vis- 

 cera, particularly in the mesenteries ad- 

 jacent to the digestive tract. They are 

 often found encysted in tightly coiled spirals 

 in the Atlantic and Pacific herrings, red- 

 fish, and many other species, and may 

 become very active when released--moving 

 in a typical whiplike manner. Numbers per 

 fish range from a few to many hundreds. 



5. AduU nematodes may also be found in the 

 digestive tract, but as a rule are not con- 

 spicuous . 



6. Larval cestodes maybe regionally abun- 

 dant in the viscera of many fish species. 

 Frequently these are larvae of tapeworms 

 which mature in sharks and skates or in 

 fish-eating birds. The larvae encyst in the 

 mesenteries or wall of the digestive tract 

 as white ovoid or club-shaped nodules, fre- 

 quently 1/8 to 1/2 inch in length. 



7. Adult cestodes inhabit the digestive tract 

 of fish, and may be recognized by their 



Figure 23.--Visceral nodules in herring caused by the fungus 

 Ichthyosporidium hoferi. 



extended white ribbonlike appearance--the 

 ribbon being composed of many egg-pro- 

 ducing segments. Such worms may occa- 

 sionally be found extruded from the vent 

 of the fish after death (this often happens 

 with smelt, for example). Worms are usually 

 few in number in any single host, but may 

 occupy the entire length of the intestine. 



SUGGESTED REFERENCES 

 General 



Allison, Leonard N. 



1950. Common diseases of fish in 

 Michigan. Michigan Department of 

 Conservation, Miscellaneous Pub- 

 lication No. 5, 27 p. 



Bang'nam, Ralph V. 



1941. Parasites of game fish. The 

 Aquarium Journal, vol. 14, No. 3, 

 p. 29-31. 



1948. Parasites of freshwater fishes. 

 State of Ohio Department of Agricul- 

 ture, Bulletin No. 229, 12 p. 



Cameron, T. W. M. 



1945. Fish-carried parasites in Can- 

 ada. Canadian Journal of Compara- 

 tive Medicine, vol. 9, p. 245-254. 



Davis, Herbert S. 



1953. Culture and diseases of game 

 fishes. University of California 

 Press, Berkeley and Los Angeles, 

 332 p. 



Haderlie, Eugene Clinton 



1953. Parasites of the fresh-water 

 fishes of northern California. Uni- 

 versity of California Publications in 

 Zoology, vol. 57, p. 303-440. 



Hargis, William J. 



1958. Parasites and fisheries prob- 

 lems. Proceedings of the Gulf and 

 Caribbean Fisheries Institute. Elev- 

 enth Annual Session, p. 70-75. 



Heller, Anita F. 



1949. Parasites of cod and other ma- 

 rine fish from the Bay of Chaleur 

 region. Canada Journal of Research, 

 vol. 27, p. 243-264. 



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