DISEASES, PARASITES, AND PROBLEMS 43 



parasite but does not respond very well to formalin. 

 It will, however, respond to quinine. 



A word of caution is in order concerning the use of 

 various chemicals for the treatment of fish diseases. 

 Fishes vary in their sensitivity to some of the chemi- 

 cals recommended. Also some medications vary in 

 their composition. Fishes weakened by disease are 

 sometimes particularly susceptible to toxicants. Tak- 

 ing these points into consideration, it is best to treat a 

 small lot of fish before undertaking treatment of large 

 numbers of fishes. When fishes are susceptible to a 

 recommended concentration, it is possible to lower the 

 concentration and increase the time of exposure. In 

 experimental work it is sometimes best to discard all 

 fish, sterilize the holding facilities and start over with 

 healthy fishes. 



Many diseases and parasites of fishes have been 

 described, but our principal interest is in the more im- 

 portant parasites and diseases that are apt to develop 

 under aquarium conditions. As will become apparent, 

 the forms that are most important are bacterial and 

 protozoan. They are, for the most part, quite con- 

 tagious and usually produce acute symptoms. 



Dietary Diseases 



Fishes may eat, grow, and appear quite healthy 

 and still develop dietary diseases and die. Since fishes 

 suffering from dietary diseases frequently exhibit low 

 resistance to infectious diseases, the cause of death is 

 often attributed to the latter. In a situation where 

 fishes remain healthy for two to three weeks and 

 then commence to show symptoms of ill health, die- 

 tary trouble should be suspected. Obviously the best 



