72 



^ 



Fig. 33. — A spore-case 



mold showing escaping swim- 

 ming spores; each of the 

 spores is provided with two 

 swimming lashes which whip 

 about in the wa'.er and propel 

 the soores. Highly magnified. 

 After Zopf. 



Minnesota Plant Diseases. 



attack healthy fish unless perhaps 

 through the respiratory system, but 

 succeed if the fish are in some way in- 

 jured, for instance at points where the 

 scales have been rubbed off. When 

 once the parasites are estabHshed they 

 gradually spread over the body of 

 the fish and ultimately cause its death. 

 The fungus produces an enormous 

 number of spores which are for the 

 most part furnished with whip-like 

 lashes for propelling purposes. Oc- 

 casionally these fish molds cause epi- 

 demics and vast numbers of fishes 

 may then succumb. The occurrence 

 of several such epidemics is known. 

 These fungi are very often the cause of 

 the death of fish in aquaria such as 

 common gold fish. The danger from 

 such fungi can be lessened by keeping 

 the aquaria scrupulously clean so as 

 to furnish little chance for the sapro- 

 phytic existence of the fungus. The 

 infected fish should be removed as 

 soon as possible to prevent the forma- 

 tion of more spores. The injuries of 

 these fungi are not confined to the 

 fish in lakes and streams but are 

 sometimes a cause of great loss in the 

 fish hatcheries where the eggs may be 

 attacked. Some of the bread mold 

 aUies are also known as inhabitors of 

 fish eggs. On the Amphibia, the 

 frogs and their relatives, few fungi 

 have been found. In this state mud 

 puppies have been observed, which 

 have been killed by certain fish molds. 

 The fungus appeared on an apparent- 

 ly healthy mud puppy as a thin filmy 

 spot which rapidly grew larger, coa- 

 lescing with other spots until the ani- 



