164 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



of about a third to half an inch. While a fish might he abundantly covered with the 

 fungus, so that in water the threads would float out in a radiating mass, when the 

 fish was removed from the water the threads, too weak to support themselves erect, 

 would collapse, and the fish would then present a slimy appearance, and would not 

 seem so badly infested. In those that were but slightly attacked the fungus was, as 

 a rule, more definitely limited to spots on different parts of the body. Usually in 

 such cases it was developed as a bunch of filaments on some bruised place. Occa- 

 sionally fish could be found on which the fungus had grown as a mass of filaments 

 covering the eyes and causing blindness. Sometimes the tail and fins had become 

 so lacerated, at least in part by the action of this fungus, as to be almost destroyed. 

 If new arrivals were affected, it was usually within a week after they were placed in 

 the aquarium that they began to show the disease plainly. Within three or four 

 days of its beginning the surface would become abnormally sliiny, when an examina- 

 tion of the epithelial debris, covering the fish, would reveal the presence of numerous 

 prostrate filaments of the fungus imbedded in this material. From these the erect 

 radiating filaments were rapidly produced, so that in a few days fully developed 

 zoosporangia could be found. 



There is no doubt that this fungus was primarily a saprophyte, as are most of its 

 family, and that its parasitic habit is a secondary acquirement. It now acts in either 

 capacity, as opportunity offers. Probably the abundance of slime on some kinds of 

 fish has much to do with the fact that the fungus obtains its first hold on them. If 

 the fish is not protected by well-developed scales, or an unusually thick skin, it is 

 especially at the mercy of its invader. Having gained entrance, the fungus makes its 

 presence manifest by causing local irritation. The blood can sometimes be seen in 

 reddish patches in and about the part affected, and the fish frequently shows a desire 

 to scratch the injured spot by rubbing against some object or scrubbing itself in the 

 sand on the bottom of its tank. In a more advanced stage the fish becomes sluggish 

 and frequently dies, when a vigorous growth of the fungus follows until bacteria put 

 a stop to it by causing putrefaction of the body. Often a badly infested fish will 

 recover, and minor attacks come and go quite frequently among the more hardy 

 species. 



None of the marine animals in the aquarium were attacked by this fungous disease. 

 In the fresh-water section a genus closely allied to Saprolegnia (Achli/a) was found 

 developed considerably on the eggs of a crayfish as they were attached to the parent. 

 Some of the turtles were said to be "fungused," but no examination was made of 

 material from this source. The growth on all the fresh-water fish seemed to be the 

 same, and in all cases a Saprolegnia. There was a difference as to susceptibility, this 

 apparently depending to some extent on the age of the fish or the species. Young 

 fish seemed comparatively exempt from the disease. If one died and remained in the 

 water it readily became covered with the fungus, but while living they were not much 

 affected. This was true even of the same species in different stages of development. 

 For example, a tank of young black bass showed no signs of disease, while mature 

 fish of that species almost invariably "fungused." 



Among the mature species there likewise seemed to be a wide difference in the 

 power of resisting infection. Undoubtedly such factors as bruises, rubbed scales, 

 changed and unusual surroundings, or insufficiently developed epidermal protection 

 had much to do in determining liability to infection. For instance, fish with a tough 





