At present there is no known control for 

 nnost parasites except in relatively small 

 bodies of water such as fish hatcheries, 

 small ponds, and aquaria. References to 

 the methods of treatment of fish parasites 

 nnay be found in Hoffman (1959). 



The major parasite groups discussed in 

 this report are listed and explained 

 below: 



Protozoa - single-celled animals, usually 

 microscopic. Parasitic groups of pro- 

 tozoa important to fishes include 

 Ciliata, Flagellata, Myxosporidia, and 

 Microsporidia; may be either external 

 or internal parasites. While the in- 

 dividual protozoan is usually micro- 

 scopic, aggregations nnay cause effects 

 recognizable by the naked eye. 



Monogenetic trematodes - External flatworms, 

 usually small, commonly calledflukes, 

 often found on the gills; are called 

 monogenetic because they complete 

 their life-cycle on one host (mono = 

 single, genetic - origin). Posterior or- 

 gan of attachment (haptor) well de- 

 veloped with chitinous clamps and 

 hooks. 



Digenetic trematodes - Internal flatworms, 

 often very small, but occasionally large 

 enough to be seen easily; are called 

 digenetic because at least two hosts are 

 needed for their life-cycle (di = two, 

 genetic = origin). Larva (metacercaria) 

 or adult may be found in fish, first 

 internnediate host is snail or clann; 

 possess oral and ventral suckers; eggs 

 present in adults which may be found 

 in alimentary tract, occasionally else- 

 where; metacercariae in various or- 

 gans (skin, muscle, mesenteries, 

 etc.). 



Cestodes - Tapeworms, are also flatwornns, 

 but are distinct from "flukes" in that 

 the adult worm is usually composed of 

 a head (scolex) and many egg-producing 

 segments. Found as adults or larvae 

 in fish; intermediate stages in "water 

 fleas". 



Nematodes - Unsegmented roundworms (ac- 

 tually cylindrical) which occur as lar- 

 vae in tissues, and as adults in the 

 alimentary tract, occasionally else- 

 where. Adult female contains eggs, 

 larva does not. 



Acanthocephala - "thorny-headed" worms, 

 which occur as larvae or adults in 

 fishes. 



Parasitic copepods - Small highly special- 

 ized crustaceans related to crayfish 

 and crabs, often called "fish lice," 

 usually found on external surfaces; 

 sonnetimes embedded, sometimes 

 loosely attached; shape may be louse- 

 like to wormlike. 



Leeches - External worms recognizable 

 by their external segmented appear- 

 ance, frequently bright coloration, and 

 a large sucker at the posterior end. 



Glochidia - Fresh-water clam larvae in 

 cysts on gills or fins of fish. 



Lampreys - Primitive fishlike vertebrates 

 and the largest of the fish parasites, 

 ranging up to 3 feet in length. They 

 may be recognized by the large cir- 

 cular mouth containing many ro%vs of 

 thornlike teeth. 



In most instances marine and freshwater 

 fish have different parasites, therefore, 

 they are discussed separately under FRESH- 

 WATER PARASITES and SALT-WATER 

 PARASITES. 



The following plan of organization is 

 followed \inder each category: 



(1) Parasites of the body surfaces and 

 gills 



(2) Parasites of the body muscles 



(3) Parasites of the viscera 



A sinnplified drawing (fig. 1) of an opened 

 fish is included to show the various organs. 



