158 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



The diseased fish could not eat, but rejected their food as if their mouths were 

 sore, and their respiration was seriously affected by the inflammation of the mucous 

 membrane of the gills. These difficulties, added to a general irritation of the skin, 

 shown by the restlessness of the fish and by their disposition to scratch themselves 

 in the sand, seem quite sufficient to account for our heavy losses among infested fish. 

 The trout exhibit was very nearly destroyed for a time, and several other species 

 were almost equally infested, but with quite various effect. The season's experience 

 confirmed the conclusions of Kerbert that this is a hot- weather parasite, since it dis- 

 appeared almost entirely from the aquarium during the month of September, as the 

 temperature of the water fell off. It is thus very likely to affect most injuriously 

 species which are most sensitive to the heat. The thickness of the skin seemed also 

 to modify greatly the effects of an attack; and this is perhaps the reason why young 

 fish are much more likely to succumb than old. Young catfish died like sheep with 

 the murrain,* but adults of the same species would become gray with pimples with- 

 out apparent suffering, and presently become clear again. Wild brook trout, brought 

 in from the streams, proved much more hardy under this disease than tame-bred 

 specimens, but all recovered as the weather cooled. 



We have no reason to suppose that this parasite is common under natural condi- 

 tions, and do not know, in fact, that it was brought into the aquarium more than 

 once. It would seem, therefore, that its ravages might be held in check by a prompt 

 recognition of it on its first appearance, and the complete isolation, or perhaps the 

 immediate destruction, of infested fish. Certainly nothing should be allowed to go 

 into an uninvested tank which has been in any sort of contact with an infested one. 

 The best remedial measure known to us is a constant and very abundant flow of the 

 clearest water obtainable. This seems not only to check the development of the 

 parasite, but also sweeps off those which escape from the tissues of the infested fish 

 previous to reproduction, and so reduces the probability of repeated infection. 



If I were again to experiment with remedies for this disease, I would construct a 

 hospital tank with hard bottom and smooth vertical sides, and with a second bottom, 

 say, G inches above the other, made of wire netting with meshes just small enough to 

 prevent the passage of fish. In this tank I would put salt so freely as to keep a layer 

 of dense salt water in the bottom of the tank the greater part of the time, but not so 

 freely as to render the water above the screen iujurious to fresh-water fish. As the 

 parasite leaves the fish and sinks to the bottom, losing its power of locomotion before 

 divhbng to give origin to young, and as when naked it is very readily killed by salt, 

 I should thus expect to prevent its multiplication in the tank, and should hope that 

 the fish infested might presently clear themselves spontaneously. An occasional dip 

 of the fish in a salt water bath wovdd probably be an aid to recovery. 



From the foregoing it will be seen that the greatest preseut problems of aquarium 

 management are those connected with the maintenance in confinement of fresh-water 

 fish. I have only to hope that this frank statement of my experience with the expo- 

 sition aquarium of the U. S. Fish Commission may contribute to the solution of these 

 problems, and help to make more easily possible to the American public a real knowl- 

 edge of the aquatic life of this country. 



"One hundred and fourteen young spotted catfish, 5 or 6" inches long, were taken out of a single 

 tank July 28, dead over night with this disease. 



