they can hardly be removed without injury to the skin. When they have become satiated 

 v;ith blood, the fish leeches leave the fish for a while, at least for the repeated 

 laying of eggs v;hich occurs in the period from Llay to autumn. In Germany there are 

 three species of fish leeches of importance: Piscicola geometra . Hemiclepsis marginata 

 and C:i''stobranchus respirans . According to the investigations of Herter, Piscicola in its 

 free life remains especially in close vicinity to the bottom on account of its stimulus 

 physiological mode of reaction. There it takes up a kind of ambush position: IVith the 

 large hind sucker it attaches to fixed objects, the remaining body is straightly extended 

 and free. Fish slii,.e is acented by the fish leeches, at least in the close vicinity. 

 Hemiclepsis lives more in medium deep and in shallov/ water. The result of this differ- 

 ence is that Piscicola occurs mainly and more frequently on large carps, Hemiclepsis 

 preponderantly on extended broodling carps and on one-year carps, Cystobranchus (spined 

 leech) is a 'Vest and South German genus, which vvas also found in Thuringia, but it is 

 generally of lesser significance in the pond industry. 



While the mating may still take place upon the fish, Piscicola and Hemiclepsis 

 deposit their eggs only on fixed objects, Hemiclepsis covers the eggs with its body 

 and later carries the liatched embryos about on its abdomen. Piscicola deposits the 

 eggs individually in hard shelled cocoons which are extra9rdinarily resistant. Strongly 

 infested ponds must therefore be limed with caustic lime after the draining in order to 

 destroy the cocoons (see Chapter VIII), 



The leeches themselves can endure dryness for a short time only. During the free 

 life Piscicola can starve for up to three months, Hemiclepsis up to ten months. 



Yi'ith stronger water currents, Piscicola is carried along in an inactive state by 

 the current. Therefore the leeches accumulate, often in large quantities, in front of 

 the sluice box during the draining of ponds and then attach themselves firmly on the 

 fishes. 



The fish leeches, next to the carp lice, are the parasites probably most frequently 

 obser\'ed by the pond operator, and which occur in the pond fisheries in general. The 

 injuries caused by them together with all the secondary manifestations are about the 

 same in kind and degree as with carp louse attack. Only poisons are not given off by 

 fish leeches. But to offset this, they are more injurious in other respects than are 

 carp lice: they transmit the blood parasite Trypanoplasma (see Chapter XV,E,1). 



The control and destruction of the parasite attached to the fish is the saune as 

 with the carp louse and is accomplished most conveniently and safely by the lysol bath, 



3. Crustacean-parasitic Diseases . 



Carp-louse attack . The carp louse (Argulus foliaceus ) which is about the size of a 

 lentil, is like the fish leech, a blood serum sucking skin parasite of the pond fishes and 

 also of the water batrachians and their larvae. It is a crustacean, no insect, which 

 latter could be supposed from its name, Vfith stronger attacks on the carps and tenches, 

 the carp louse becomes especially burdensome by the strong restlessness of the fishes and 

 the skin destruction v;hich leads to redness, mold invasion and bacterial infection, to 

 attack by one-celled skin parasites, and even to the formation of wound pocks at puncturea 

 places, A weak attack is mostly not injurious to the fishes. Only small brood suffers 

 from even a few punctures and fran the simultaneous elimination of poisons into the skin 

 with resultant severe pain. The brood may perish rapidly. SpaTm fishes are therefore to 

 be carefully freed of carp lice. On larger fishes, and of course, especially on tenches, 

 I have found thousands of carp lice, without it having caused the death of the fishes. 



The carp louse leaves the fish to mate and deposit the eggs. It can even live without 

 a host for about three v;eeks during the height of summer. Its stimulus-physiological 

 behavior to light and gravity causes it to remain near the shore about 5 to 10 cm. (2 to 

 4. inches) above the bottom, as Herter has shown. Here, of course, also live the hosts, 

 the fishes, for which the carp louse does not possess a special scenting power operating 

 at a distance. The eggs are deposited in small groups of up to 20 eggs or in bands of 



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