B. Classification of Pond Diseases . 

 From causative viewpoints, the different fish diseases may be divided as follows: 

 I. Non-parasitic diseases. 

 II. Parasitic diseases: 



A. Fungus diseases: 



(1) Mold-parasitic diseases (Mycoses) 



(2) Bacterial-parasitic diseases. 



B. Animal-parasitic diseases: 



(1) Protozoan-parasitic diseases. 



(2) Wonn-parasitic diseases. 



(3) Crustacean-parasitic diseases. 



Various other principles for the classification of the fish diseases and for 

 simplifying the review, can be applied. The diseases may be differentiated by the 

 nature of the afflicted organ into diseases of the skin, gills, kidneys, etc. There 

 are carp, tench, and trout diseases, spring, summer and winter diseases, brood diseases 

 and diseases of larger fishes, storage diseases, diseases caused by external or internal 

 parasites, individual sickness and mass epidemics of larger stocks. 



C. Non-parasitic Diseases . 



"Diseases, caused by "sour water". In heath and moor regions, with very calcium- 

 poor water, carp are easily exposed to severe epidemics, especially in winter or after 

 heavy rains. Losses can be great and the cause lies in the gradually, and naturally, 

 increasing acidity of the water, with a corresponding drop of the pH value below the safety 

 point. In many cases, sulfuric acid is the cause, while in others organic acids are respon- 

 sible for these conditions. 



A long-lasting pH value of about /;.8, causes in carps (according to Schaeperclaus 1926) 

 a milky turbidity in the skin and gills, destruction of the gills with succeeding fungus in- 

 festation and the formation of brown surface coatings (similar to that following gill rot). 

 Frequently the skin becomes more or less reddened. In the presence of Iron, higher pH values 

 of about 5.5 become dangerous for carps, according to Schaeperclaus. Iron then precipitates 

 in large flakes upon the alkaline gills (see Chapter I,E,ji). However, in accordance with local 

 conditions, the total pathological manifestations can be more or less lacking. Trout are more 

 sensitive, pikes and tenches less sensitive to lowerings of pH values, than are carps. 



The movements of the carps during the course of the typical illness become more and more 

 apathetic. It is characteristic that the fishes frequently remain stationary in a normal 

 position at the shore even after death. 



Not seldom, even at temperatures of U to 5°C, a seoondaryattack of constipation is 

 added to the illness by acid water, which strongly aggravates the course of the disease. The 

 control of the "acid sickness" is accomplished with liming according to methods discussed in 

 Chapter VIII. Fishes already strongly sickened can no longer be saved. Also trout eggs, 

 according to Schaeperclaus, perish and become moldy (see Fig. 30) with a long continued pH 

 value of /i.8, and again a content of iron in the water aggravates the condition. 



Oa.ll cover Perforation . The highest point of the large gill cover — in carp — appears 

 often more or less gnawed at. In some pond fisheries real perforations of the gill cover 

 "attack" great numbers of these fish. The primary cause for this affliction according to 

 Schaeperclaus is the brushing of the fish against rough pond walls. The irritated 



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