AILMENTS AND DISEASES 



sporangium. They subsist on the juices of their host. Other forms are 

 parasitic upon either growing or dead and decaying plants. 



Parasitic Fungi. The aquatic forms of this order, the Phyco- 

 mycetes, found on animals and plants, consist of densely interwoven 

 masses of cellular filaments, which terminate in or constitute the rootlike 

 mycelium, from which hyphae and spore capsules are developed. With 

 some species there is but a single hypha with reproductive bodies at the 

 ends, this being the case with the more ordinary forms which affect the 

 freshwater fauna. As fungi contain no chlorophyll they must take up and 

 assimulate nutritive substances from other organisms and are therefore 

 either saprophytic or parasitic. 



The Phycomycetes are separated into five groups or sub-orders: i,the 

 Clytridiacea, of which a considerable number of species are parasitic upon 

 Protozoa, Anguillulae, Rotifera, Algae and Saprolegnia; 2, the Ancylistacea, 

 parasitic upon Conjugatse, Chlorophycese and Anguillulse; 3, the Monoble- 

 pharidace^, nearly all saprophytes; 4, the Peronosporace^, of which one 

 genus, Pythium, has species parasitic on water plants and saprophytic on 

 organic substances; and 5, the Saprolegniacea, the order of greatest interest 

 to the fish-culturist, as of all the above, this group and the Peronosporacea 

 are, to greater or lesser degree, aquatic at some or all stages of their 

 existence. Most of the Peronosporaccie are aquatic only at certain stages 

 and afterwards become land forms, but the Saprolegniacea are aquatic at all 

 stages. 



Saprolegniace^. This group of water molds contain both fresh 

 and saltwater forms, of which the genus Saprolegnia is widely dessemi- 

 nated in all bodies of freshwater. The most generally distributed genera 

 are Saprolegnia, Pythiopsis, Dichtyuchus, Achlya, Aphanomyces, Leptomitus and 

 Apodachlya, present as saprophytes on dead and decaying aquatic animals 

 and vegetal substances, and as parasites on all aquatic fauna, including the 

 spawn and young and mature fishes, whenever the conditions favor their 

 active development. This occurs on skin abrasions, bruises, wounds, loss of 

 a scale, or on a torn or congested fin. When fishes are enfeebled and the 

 mucus coating affected, when they are kept under unsanitary conditions or in 

 too cold water, these fungi may develop to cover the entire body, first as 

 a film and later as white or colored blotches on the head and body, in the 

 mouth and gills, on the fins and on and under the scales, which they 

 often force out of place; as, when once established upon and into the 

 living tissue, they ultimately cause its destruction. Investigators have 

 determined that the Saprolegniacese on fishes can be communicated to 

 dead insects and those growing on dead insects and other low forms of 

 aquatic fauna are communicated in their turn to living and healthy fishes. 



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