DISEASES, PARASITES, AND PROBLEMS 49 



low ulcerations, and the fins may become frayed. The 

 infection eventually becomes general and the bacte- 

 rium can be found infecting the internal organs. 

 Microscopic diagnosis is possible since the bacterium 

 has a characteristic appearance: a long, thin rod with 

 an oscillating motion and a tendency to congregate 

 into columns (see also Snieszko 1958b). 



For the control of columnaris, Davis ( 1956 ) recom- 

 mends 1:2,000 copper sulfate dip repeated two or 

 three times at 12 to 24 hour intervals when the dis- 

 ease is in its early stages. Fishes having extensive 

 lesions should be discarded. O'Donnell ( 1941 ) recom- 

 mends a treatment of 1:15,000 solution of malachite 

 green for 10 to 30 seconds. 



Ulcer disease caused by the bacterium Hemophilus 

 piscium is not dealt with in detail here because it ap- 

 pears to be fairly well limited to trout. Persons inter- 

 ested in this disease are referred to Piper (1958). 



Protozoan Parasites 



The following is not meant to be a complete 

 treatment of the protozoan parasites of fishes. The 

 more common forms are hsted to serve as an example 

 of the symptoms, identification and treatment of this 

 type infection. The reader is referred to the excellent 

 review by Davis (1956). Much of the information 

 given here is based on Mr. Davis' book. 



Costia nectris and C. pyriformis are external para- 

 sites affecting both coldwater and warmwater fishes. 

 They cause a bluish or gray film to form on the fish's 

 body, but diagnosis should be made by microscopic 

 examination. Costiasis is considered to be a rapidly 

 fatal disease but has been successfully controlled by 



