Worm Cataract . 'A'orm cataract causes greater losses especially with trout brood. 

 The instigators are the larvae of the trematode worm Hemistomum spathaceum which the 

 trout preponderantly serves as the second intermediate host, whereas the snails (Limnaea) 

 are the first intermediate hosts. In the snail the migratory larvae with forked tails, 

 so-called fork-tailed cercaria are developed, which seek fishes swimming about freely in 

 the vvater. According to ffunder (1926) they can remain alive in the water for only about 

 a day. Carps of 5 centimeters length in small brooks can succumb in 15 to 30 minutes 

 to the mass attack of forktail cercaria. With a weaker attack the larvae migrate to the 

 eyes of the fishes and attack the lens chamber and the lens. The larvae on penetrating 

 the fish have cast off their tails. The attack on the lens causes cloudiness and there- 

 by "wona cataract". The blind fishes grow more poorly, perish in part, and fall easy 

 victims to fish foes. The main hosts of the worms are gulls and other water birds. 

 Since a sufficient eradication of the snails is often not possible in trout growing 

 fisheries, it also becoues necessary to keep birds at a distance in order to control 

 the disease. 



Dactylogyrus diseases . The trematode worms of the genus Dactylogyrus are probably 

 the most frequent gill parasites of the pond fishes. They are of many species, and 

 occur with all species of fishes. As with other animal parasites a weak attack is com- 

 pletely harmless, a stronger attack not only by D. vastator . but also by all the species 

 named below, causes strong injuries of the fish brood according to my observations. 

 The dactylogyrae are identified by a four-tipped head which has four black eyes, and 

 a large posterior suction disc with two characteristically formed "central hooks", 



With carps there are frequently three varieties: Dactylogyrus vastator . size up to 

 1 millimeter, central hooks relatively small, with two processes at the root, D. anchor- 

 atus . up to 0.6 mm. long, central hooks very large, one root process, and D. minutus . 

 up to 0,5 mm. long, central hooks relatively small, two unequally long root processes, 



Dactylogyrus minutus is found above all in the autumn in larger carps and locates on 

 the upper end of the gill lamellae, D. anchoratus is found throughout the entire year in 

 large and small carps and locates in the middle of the gill lamellae, D. vastator attacks 

 the gill ends and occurs preponderantly in the siimmer with carp brood. With tenches, 

 I have often observed D. macracanthuS p which is up to 1 mm. long and has two large central 

 hooks in the adhesive disk each with two very broad root processes, 



D. vastator was first described in 192/1 by the Swede Nybelin, and was recognized as 

 the main instigator of the dactylogyrus disease, the most frequent carp brood disease. 

 Since then very much has been written about it. Nordquist believed he must conclude 

 from observations and from experiments, that the infection of the carp brood originates 

 from the pond bottom. Nybelin 1925, actually succeeded in proving, that with the be- 

 ginning of lower temperatures (under 15°C.), D. vastator forms larger "winter eggs" which 

 sink to the bottom, after which the gill parasites perish. 



In 1929 Spiczacow pointed out, that the assumptions of Nordquist and Nybelin, which 

 were also assumed by Wunder are not sufficiently proven. He furthermore states with 

 justice, that even if winter eggs did occur there was no available reason to assume that 

 the pond bottom was the only source of infection. I must also say that the few experi- 

 ments of Nordquist are not conclusive. Many of my observations, such as the strong 

 occurrence of the disease in newly constructed ponds contradict the theory of the Swede. 

 Since the extending ponds are fished out beginning July, often even in June, it also is 

 unexplainable how the winter eggs are to sow the pond bottaa when they are first developed 

 in September, Nordquist himself found moreover the presence of D. vastator in April in 

 yearling carps, Wunder found it in spawn carps and in larger carps. In the winter and 

 spring some Dactylogyrus larvae are always found on spawn carps, which can very well 

 belong to the variety D. vastator . Finally Kulwiec in 1929 has verified, that D. vastator 

 has free swimming ciliated larvae which Just like Costia and other parasites which set 

 in with D. vastator . can invade the brood ponds or can transfer frcrn parent fishes to 

 the brood during the spawning activity. Of course, they are not capable of living long. 



Fortunately it has been shown from my own investigations, also from those of 

 Buschkiel, Vfunder and other authors in many pond fishery operations (Schaeperclaus, 1930) 



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