50 MAINTAINING FISHES 



three different procedures: a one-minute dip in a 

 1:500 solution of acetic acid, 12-hour treatment of 1 to 

 20,000 formalin, and a one-hour treatment in a 1:500,- 

 000 solution of pyridylmercuric acetate (pma). 

 Some fishes are sensitive to these treatments ( see also 

 Fish 1941). 



The genus Chilodon includes a number of fish par- 

 asites. As is the case with many parasites, they become 

 a serious problem when fishes are crowded or become 

 weakened. The most evident symptom is a tendency 

 for the host to become weak and emaciated. Diag- 

 nosis is by microscopic examination of scrapings from 

 the infected fish. The organisms are usually concen- 

 trated on the gills. Control is by a short dip in a 3 

 percent solution of common salt, a one-minute dip in 

 glacial acetic acid diluted to 1:500, or a 12-hour treat- 

 ment of 1 to 20,000 formalin. 



Ichthyophthirius multifiUis is one of the easiest of 

 diseases to diagnose. It appears as uniformly-shaped 

 white specks scattered over the host. Both the adult 

 form and the encysted form are visible without mag- 

 nification, but identification should be verified by 

 microscopic examination of the fins and body of the 

 fish. The control of "ich" is compHcated by the occur- 

 rence of an encysted stage which is not affected by the 

 usual treatments for external parasites. The parasite 

 may be partially controlled by placing the fish in run- 

 ning water for three or four days. (Maintaining the 

 aquarium water at 85° F. for several days will con- 

 trol "ich" on tropical fishes.) But where fish are con- 

 fined in smaller tanks, a more convenient treatment is 

 with quinine sulfate. Five-tenths grains or 0.032 grams 

 per gallon of water is added to the holding tank, and 



