
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. 100. Argulus catostomt, a Crustacean i i 
parasite. Enlarged ventral and dorsal views, and The general American freshwater form is 
natural size. 
Argulus catostomi, Fig. 100. Other com- 
mon Crustacean parasites on the gills and surface of freshwater fishes are 
Achtheres lace, A. percarum, Ergasilus funduli, Lerneopoda fontinalis, L. 
siscowet, L. coregont, 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 affect fishes and 
_amphibia they will not be further mentioned, though many of the aquatic 
insects and their larve 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 Bacteride, Sporozxoa and Infusoria. 
BacTerip&. This section of the Protozoa includes orders which 
are both saprophytic and parasitic, potent factors in the causation of 
153 
