170 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



was tilled with this water which was left running in the ordinary way for about a 

 week, care being taken to dip nothing into the tank. A few days after the tank had 

 been cleaned the filter seemed to work imperfectly, the water in all the tanks becom- 

 ing cloudy. The fish selected for this special tank was the small-mouthed black bass, 

 a species which had "fungused" somewhat readily. Twenty-three of the best speci- 

 mens of a car-load were selected and placed in the prepared tank, the remainder of the 

 lot being placed with fish that were more or less infected. None of the fish showed 

 signs of the disease when taken from the car. Cultures made from water taken 

 from the tank just after it was cleaned gave a very slight growth. Water taken from 

 the tank the fifth day after cleaning gave no growth, while other cultures attempted in 

 the filtered water, both before and after its entrance into the tank after the fish were 

 placed in the tank, once gave Saprolegnia and once failed. This would seem to indicate 

 that the zoospores were present in the water, though in comparatively small numbers. 

 As the tank was so thoroughly cleaned, the only possible source of infection in this case 

 was the water supply. Four days after the fish were placed in the tank they began 

 to have the very slimy appearance that accompanies the first stage of the fungous 

 attack, and an examination of this slime showed that fungous threads were present, 

 though not yet abundant. The bass that were placed with diseased fish seemed but 

 little more parasitized, but later both lots became badly diseased, and in a fortnight 

 were practically all gone. 



The above experiment and the cultures made from the aquarium water before its 

 entrance into the tanks show clearly that the original source of infection was the 

 water supply — a difficulty it would seem impossible to remedy, at least with an imper- 

 fect action of the filter. * 



It has long been known that species of Saprolegnia are sometimes found as para- 

 sites on aquatic animals. They are closely related in their structure to certain algae, 

 and may be regarded as degenerated forms, which, because of their saprophytic or 

 parasitic habits, have lost their chlorophyll. We are indebted to such investigators 

 as Cornu, Pringsheim, and Be Bary for much of our knowledge of the life-histories 

 of these forms. Concerning the fungus most frequently found as a parasite on fish, 

 English and Scotch writers seem to have written most, a fact due perhaps to the 

 great outbreaks of the disease among the fish in the rivers of Great Britain in the 

 years 1877 to 1880, during which time the loss was so great as to seriously interfere 

 with the fisheries industry. Many kinds of fish were affected, but the salmon most 

 disastrously. About the same time certain authors note an unusual occurrence of the 

 disease among the fish of sonic of the rivers of this country. 



Our American botanists have done comparatively little with this class of fungi. 

 The most elaborate work is a monograph by Humphrey, treating of American forms, 

 and giving the general life-history and the literature of this group, lline (1878) pub- 

 lished a general article on this class of fungi, and Galloway (1891) has dealt with the 

 life-history of Saprolegnia monoica. Gerard (1878) and Lockwood (1S!>0) have published 

 articles treating of the special fungus of fish called by them S.ferax; otherwise — if we 

 except the articles copied in American publications from foreign sources — our litera- 

 ture on the subject seems to be limited to mere references to S. ferax as a parasite of 

 fish in certain places. 



"This filter w.as heavily overtaxed at the time, usually filtering more than twiee the amount of 

 water for which it was intended. 



