and vdth the deterioration of living conditions. A stronger attack always leads secondar- 

 ily to invasion by molds, invasion by bacteria, to attack by the microscopic trenatode 

 worm G;Todactylus and finally even without this to a more or less rapid death. Costia 

 and Chilodon laay occur equally abundantly in the v/inter or in the warn summer. Chilodon 

 attack is a frequent late winter disease of the carps. I h--ve personally found an 

 abundance of Costia even at temperatures below 2°C. This can then also lead especially 

 to the disease of the carp noses v;ith a secondary mold infection. Chilodon is to Vje 

 found ver;.^ seldom in trout. It is not yet taovm whether Costia can fortn resistant cysts 

 which will endure hibernation on the pond bottom. The question is also less important 

 practically, vdth the discussed character of the diseases. Cyclochaete is the least 

 dangerous of ail three of the parasites. 



For the control of the contagious skin and gill turbidity the fishes are bathed for 

 15 to 30 minutes in a 2.5 percent solution of table salt (2.5 kilograms of salt in 100 

 liters of water). Zinc or zinc coated utensils must not be used for this purpose, be- 

 cause poisoning of the fishes by zinc chloride would result, A temperature increase of 

 about 2 to 3°C. is particularly effective accordinf^ to Plehn (1927), After the bath the 

 fishes may be rinsed in water which is about one degree v.-armer. Then they must be set 

 out in unobjectionable, richly nutritive ponds. In a reservoir the disease would soon 

 revive, inasmuch as all the parasites can never be completely removed. The lysol bath 

 also v^orks ver;r v;ell against chilodon. The bathing of the spavm fishes immediately 

 before setting them into the spav.Tiing ponds and catching them outright after they have 

 spawned, feeding of the brood ponds out of fish- free waters, the keeping out of wild 

 fishes which are often parasite carriers, protects the brood against the first infection. 

 Good and effective nutrition decreases the danger of illnesses. 



Amoeba Infection . Anoeba infection of the trout kidney is an infrequent disease. 

 I observed it once in the autumn in a large natural pond, where many rainbov/ trout 

 showed a fat abdomen due to considerable kidney swelling. 



Ichthyophthirius-attack , Ichthyonhthirius nultifiliis ,a relatively large, spherical 

 parasite havinj a diameter 01 mostly 200 to /tOO im, but often up to 1000 mu or 1 milli- 

 meter, lives in the skin and in the gill epithelia. It may occur in all pond fishes. 

 Large fishes are mostlj'- so weakly attacked, that the parasites do them little ham. 

 A.Mong the brood of carps, tenches and trout, hovfevcr, ichthyophthirius frequently causes 

 great destructions. Gritty pimples can then be detected on the skin and gills (Fig. 68), 

 A stronger attack of ichthyophthirius most alv/ays leads to the loosening of more or less 

 large epidermal shreds, to bacteri.al infection and to mold invasion of the skin. 



Hg. 68, Tail fin of a tench of 4 cm. 

 Photograph of a stained preparation, 

 horseshoe-shaped nucleus . 



204 



length with ichthyophthirius, 

 The paras is te contains a 



f 



