5a MAINTAINING FISHES 



genus Gyrodactylus and Dactylogyrus, however, con- 

 stitute an exception. Parasites of both these genera 

 complete their life cycle on a single fish host and are 

 capable of building up heavy infestations. Transmis- 

 sion is by contact. Gyrodactylus occurs mostly on the 

 fins and body of the host fish. It gives birth to well- 

 developed young. Dactylogyrus parasitizes the gills of 

 fishes. It is an egg-layer and reproduces somewhat 

 more slowly than Gyrodactylus. Control is by a 12- 

 hour exposure to 1 to 20,000 formalin. A two-minute 

 dip in 1:400 solution of acetic acid has also been rec- 

 ommended. 



Parasitic Copepods 



Two important warm-water parasitic copepods 

 may be encountered on captive fishes. They belong to 

 the genera Argulus and Lernaea. The fish louse, 

 Argulus spp., moves at random over the host's body. It 

 may be more than a quarter of an inch in diameter 

 and, of course, visible to the unaided eye. 



The anchor worm, Lernaea spp., once estabHshed, 

 is a considerably more serious parasite than the fish 

 louse. It has a complex life cycle involving a free- 

 swimming stage, reproductive stage on the gills of 

 fishes, and the female has an attached stage during 

 which the eggs are developed. The latter stage is usu- 

 ally observed. This form may be as much as a half 

 inch in length. It appears as a boney splint protruding 

 from the body of the host. It does considerable me- 

 chanical damage to certain fishes such as the goldfish 

 and golden shiner. 



No entirely satisfactory control exists for the par- 

 asitic copepods. Their tough body covering protects 



