high oxygen requirement. Also variations of the pH value from the normal which are 

 especially well tolerated by the molds in general, stimulate the occurrence of the gill 

 rots. In ponds in which gill rot has once been present and in neighboring ponds it will 

 easily recur in succeeding years. 



The attack by this instigator is not always deadly. There are cases in which no 

 illnesses are observed at any time, Besides this, diseased gill parts can slough off, 

 so that sharply defined gaps are formed in the gills which gradually heal again in the 

 course of more than one year (Schaeperclaus) , Until that time the fishes are feeble and 

 less capable of growth, hence of lesser value as stock. The sloughing of gill parts at 

 the same time serves the distribution of the spores. 



Fishes which have been sick for several days, have an empty intestine and often 

 gather at the inflow. Saaetimes the beginning of the sickness is also indicated by the 

 refusal of food. A control is possible by the introduction of cool water, removal and 

 prevention of water turbidity and organic pollution, temporary discontinuation of feed- 

 ing especially in warm weather, liming and thorough drainage of the bottom immediately 

 after the fishing out. A liming of the v/ater is also reconmended (see Chapter VIII ), 

 but I have been able to determine that losses stopped just as quickly when no liming 

 was done . 



Fig. 65, Gills of a two— summer carp with gill rot. Exposed by 

 the removal of the gill cover. The ends of the upper gills are 

 completely destroyed by the infection, the diseased portions 

 have already cast off to a large extent. 



2. Schizomycete Parasitic Diseases . 



Red plagues . There are various, often individual, metabolic-physiological diseases 

 which are accompanied by red coloration (Schaeperclaus, 1929). The true red plagues, in 

 which inversely the red coloration can also be lacking, have their origin in bacterial 

 infections. Two instigators for carps have thus far been described: Bacterium cyprinicida 

 Plehn and Pseudomonas plehniae Spiekermann and Thienemann. Both diseases are not very 

 frequent at present. The control must be the same as with the followJLng plagues. 



Birunculosis . FUrunculosis is the most dangerous plague of the trout, and especially 

 of the brook trout, less of the rainbow trout. Its instigator is the bacterium salmonicida 

 Emmerich and TTeibel, a nonmotile short bacillus, which produces a characteristic brownish- 

 black pigment when grown on artificial culture media. The bacterium prefers organically 

 polluted water and sojourns for longer periods in mud. The disease manifests itself partly 

 in muscle ulcers which can break out to the exterior (see Fig. 66), partly also only in 

 blood-shot places, intestinal disorders, etc., and even all external sjTnptoms may be lack- 

 ing. The losses are mostly very great. The plague may be easily introduced by purchased 



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