liver which leads to dropsy of the abdomen (acoanulation of fluid in the abdominal 

 cavity, Fi^. 67) in the spring, general infection and thereby to great losses. The 

 carp-like fishes with their strongly lobed livers are naturally ver^' susceptible to 

 this disease. In the chronic course of the disease, flat ulcers of the skin and muscles, 

 which open to the outside, can occur, and the accumulations of fluid in the abdominal 

 cavity, which have given the naime to the disease, maj' be lacking. The peak of the 

 mortality occurs each year in April and llay. The primary infection may have already 

 taken place in the previous year. The main danr^er of Illness exists in the hibernation 

 pond, when the cold-loving bacteria can increase undistmbed in the intestine and cannot 

 be carried away by food constituents traversing the intestine, 



Sonetiraes the disease does not becone evident until many weeks after the infection 

 starts. The best methods for control in addition to those mentioned with furunculos is , 

 general measures for epidemic control are: The care of hibernation ponds by drainage 

 throughout the entire summer, protection of the fishes in the autumn and vdth ever;.' 

 fishing out, not too narrow hibernation, hibei-nation of one-year c^rps in brood extend- 

 ing ponds (see Chapter IV), feeding in winter, avoidance of too strong feeding, especially 

 vti.th brood of only few centimeters length, avoidance of Icnr atorare, well planned culture 

 of resistant races. Infected ponds must be lir.ed as thoroughly as possible because the 

 disease instigators can endure a Ion" drjTiess, Liud is to be removed by suitable measures 

 (see Chapter \rill). Diseased animals recover quickest ia floTdng water. A spread of the 

 disease into natural v/aters must be avoided as it can easily cause a new infection. 



If the plague has once becone firmly established in a pond fisherj', whereby the 

 bacteria presumably pass through an occasional saprophytic :node of life in the mud, then 

 their removal is practically impossible for years. A rapid, thorough interference, 

 removal of all sick stocks, drainage of the ponds for longer periods must therefore not 

 be avoided at the first appearance of the plague. Under no circumstances may fishes out 

 of infected stocks — no matter how healthy they seem — be mixed -^dth healthy stocks 

 and new generations (for example with hibernation). They mostly always have a latent 

 (hidden) infection. The losses have (according to Schaeperclaus) often been 90 percent 

 ap.d more, the danger of infection of the remaining fishes, and the danger of the obscure 

 infection of the total fish stocks in greater than with all other diseases. The simulta- 

 neous existence of secondary' skin diseases caused by one-called animal parasites, can 

 mislead the investigator in the determination of the kind of disease. 



E. Anjjnal Parasitic Diseases , 



1. Protozoan Parasitic Diseases , 



Contagious Skin and Gill Turbidity . A whitish-bluish turbidity (often associated with 

 reddening) and a disease of the epidermis is caused in pond fishes of ever;- kind and size 

 in by far the most of cases by the strong attacks of one-celled parasites of various kinds: 

 The flagellate Costia necatrijc up to about 20 mi long, the heart-shaped ciliated animal 

 Chilodon cyprini of about 70 mi length and the circular ciliated animal Cyclochaete 

 (various species) of 9 to 50 mu diameter. All three parasites react about the same. They 

 especially prefer to become established as secondary' phenomena with other diseases, with 

 skin injuries or with the deterioration of the general living conditions of the fishes. 

 Turbidity of the skin is often rightfully regarded as a "storage disease" and is in manj' 

 respects a secondary disease similar to the saprolegnia infection, 



Chilodon still in first place, and with brood, of course, also Costia and Cyclochaete 

 arc to be regarded as primary, dangerous disease instigators. In many cases of disease 

 the gills are attacked in stronger m.easure than the skin, and then likewise show an 

 easily visible whitish coating. The parasites have a tendency to take up a temporary life 

 of freedom in the water, even though they are true parasites, and in this way they can 

 seek out and infect a new host and can be transferred by outflowing vfater (see Chapter IV). 

 A weak latent attack by one or the other parasite happens continually in most of the pond 

 fisheries and does no harm. It only becomes dangerous with the appearance of injuries 



