FISH HEALTH MANAGEMENT 315 



wet gill tissue (lOO x or 440 x) if nonseptate hyphae and spores of the 

 fungus are seen in the capillaries and tissue of the gill lamellae. Suspect 

 material should be sent for a confirmatory diagnosis. Suspect fish should be 

 held under strict quarantine until the diagnosis is confirmed. 



There is no control for branchiomycosis except destruction of infected 

 fish and decontamination of facilities. 



Protozoan Diseases 



Protozoans probably cause more disease problems in fish culture than any 

 other type of fish pathogen. Fish reared under intensive conditions rarely 

 are without some parasites. It is common to find protozoans of many taxo- 

 nomic classes in or on wild fish. When present in small numbers, they usu- 

 ally produce no obvious damage; in large numbers they can impair the ep- 

 ithelium and actually feed on the cells and mucus of the fish. To discuss 

 each protozoan and parasite of fish in this text would be a lengthy task. 

 Therefore, only those of major importance to fish husbandry are presented. 

 For those who wish additional details, a search of the literature will reveal 

 many comprehensive works. Hoffman's Parasites of North American Freshwa- 

 ter Fishes (1967), is an excellent source with which to begin. 



External Protozoan Diseases 



ICHTYOBODO 



Species of Ichtyobodo (Costia) are very small flagellated ectoparasites easily 

 missed during routine microscopic examinations of gills and body scrap- 

 ings. These protozoans are free- swimming, move by means of long flagella, 

 and are about 5 by 12 micrometers in size — about the size of a red blood 

 cell (Figure 87). Two species, /. pyriformis and /. necatrix, are commonly 

 seen and produce "blue slime" disease of fish. The characteristic blue slime 

 or bluish sheen taken on by fish is caused by increased mucus production 

 in response to irritation. 



An early sign of an Ichtyobodo infection is a drop in appetite of the fish 

 and a general listlessness. "Flashing" may be evident if the skin is infected, 

 but only rarely if just the gills are involved. Signs of the disease sometimes 

 are mistaken for bacterial gill disease. Heavily infected fish often develop a 

 bluish slime over the entire body (Figure 88); however, fish less than 3 or 4 

 months old usually will die before this condition develops. 



