AILMENTS AND DISEASES 



mostly of the first-named genus; of which some are marine and others 

 freshwater forms. Those on migratory fishes are able to change with their 

 hosts from salt to freshwater and the reverse. They are wholly external 

 parasites, either in the gills or on the surface, and frequently change their 

 host, though each species prefers a certain genus or closely related kinds, 

 to which it is usually confined. They have a flat rounded carapace, 

 notched on either side and bluntly projecting in the centre, nearly trans- 

 parent, and elegantly marked in colors; smooth above and armed below 

 with spines to attach themselves on the surface of their hosts, to which 

 they also cling by anterior maxillipeds which are modified into sucking 

 discs, and by clasping posterior legs or maxillipeds. They can swim freely 

 and the males frequently abandon their hosts in the breeding season, as 

 do also the larger females, at times, as unlike other copopods, the hun- 

 dreds of eggs are not carried in sacs but are fastened in rows on objects on 

 the bottom. As their food is the blood of their host, extracted through 

 the sucking discs, they are destructive parasites which become serious 



menaces, especially in the confines of the 

 aquarium, where they are prevented from 

 changing to a number of fishes. They 

 are of frequent occurrence on both pond- 

 raised and imported goldfishes, usually 

 easy of detection by their size and shape. 



FIG. loo. yirru/us catosiomi, a Crvatacenn , ■ i a • r i c 



parasite. Enlarged ventral and doreai views, and The general American trcshwater torm IS 

 natural size. Avgulus catostomt. Fig. lOO. Other com- 



mon Crustacean parasites on the gills and surface of freshwater fishes are 

 Achtheres laca, A. -per car urn, Ergasilus funduli, Lernao-poda fontinalis, L. 

 siscowet, L. coregoni, L. pomotidis, Lamproglena pulchella; and Lepeophtheirus 

 salmonis on Salmon in freshwater. 



Insecta or Insect Parasites. This group includes the Lice, 

 Fleas, and other insect tormentors. As they do not aflfect fishes and 

 amphibia they will not be further mentioned, though many of the aquatic 

 insects and their larvae could be included in this group. They are else- 

 where mentioned and described. 



Protozoa or Protozoan Parasites. This group embraces the 

 lowest forms of the animal kingdom; organisms possessing but a single 

 cell or colonies of unicellular beings. They are divided into 4 sections, 

 4 classes and 21 orders, many of the 38 genera of which are for the most 

 part entozoal, but some are ectozoal parasites. The sections of interest 

 to the fish-culturist are the Bacterids, Sporozoa and Infusoria. 



Bacterids. This section of the Protozoa includes orders which 

 are both saprophytic and parasitic, potent factors in the causation of 



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