314 FISH HATCHERY MANAGEMENT 



Fungus Diseases 



Fungi are encountered by all freshwater fishes at one time or another dur- 

 ing their lives. Under cultural conditions, certain fungi can be particularly 

 troublesome. Species of the family Saprolegniaceae commonly are implicat- 

 ed in fungal diseases of fish and fish eggs. Species of Saprolegnia, Achlya, 

 Aphanomyces, Leptomitus, Phoma, and Pythium have been reported as patho- 

 gens. Fungae infestating fish or eggs generally are considered to be secon- 

 dary invaders following injury but, once they start growing on a fish, the 

 lesions usually continue to enlarge and may cause death. Fungi often at- 

 tack dead fish eggs and spread to adjacent live eggs, killing them. These 

 fungi grow on many types of decaying organic matter and are widespread 

 in nature. 



The presence of fungal infections on fish or fish eggs is noted by a white 

 cottony growth. This growth consists of a mass of filaments; these contain 

 the flagellated zoospores that escape to begin infections on other fish or 

 eggs. Unless control measures are taken, the expanding growth ultimately 

 may cover every egg in the incubator. 



Injuries to fish produced by spawning activity or other trauma, and le- 

 sions caused by other infections, often are attacked by fungus. Holding 

 warmwater fish in cold water during summer can render fish more suscepti- 

 ble to fungal infections (Figure 86). 



Good sanitation and cleanliness are absolutely essential to effective con- 

 trol of fungi and other parasites under intensive culture conditions. For the 

 control of fungal infections on eggs, there are two methods, one mechanical, 

 the other chemical. The mechanical method is used for controlling fungal 

 infections on both salmonid and catfish eggs, and involves picking dead 

 and infected eggs at frequent intervals during incubation. This, however, is 

 time-consuming and some healthy eggs may be injured in the process. 



Good chemical control of fungal infections on eggs can be achieved. For- 

 malin at 1,600 and 2,000 parts per million for 15 minutes will control 

 fungus on both salmonid and catfish eggs. Do not expose fry to these con- 

 centrations of formalin. 



In Europe, gill rot, a disease caused by fungi of the genus Branchiomyces, 

 is considered one of the greatest threats to fish culture. Although European 

 gill rot is primarily a disease of pike, tench, and carp it has been found in 

 rainbow trout, largemouth bass, smallmouth bass, striped bass, northern 

 pike, pumpkinseed, and guppies in the United States. This disease has 

 been found in Alabama, Arkansas, Florida, Georgia, Missouri, Ohio, Rhode 

 Island, and Wisconsin. 



Clinical signs associated with branchiomycosis include pale, whitish gills 

 with necrotic areas, fish gasping at surface, and high losses. 



A presumptive diagnosis can be made by microscopic examination of 



