154 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



water habit. Our own fresh- water collection, which usually contained over a hundred 

 species, represented by two or three thousand specimens, was probably the largest 

 ever maintained, and the previous experience of our aquarium superintendents having 

 been chiefly with salt-water forms, the difficulties impending were not fully appreciated 

 in advance. Our determination to be visibly ready May 1* forced us to do some 

 things which would not have been admissible under other circumstances. 



The great obstacle to the successful and economic maintenance of a fresh-water 

 aquarium is the liability of many species to parasitic disease, either that due to 

 saprolegniaceous fungi (with which we were already very well acquainted) t or to that 

 caused by a protozoan parasite not hitherto reported for this country, and but little 

 known in the Old World. 



Fungous parasitism began with especial virulence very early in the season — a 

 fact to be attributed partly to the enforced hurry of our preparations, which made it 

 impracticable to assort or quarantine our specimens as they came in, and partly to a 

 delay in placing the filters, on which account we were obliged to keep our material for 

 some weeks in unfiltered water. 



The plant parasite causing this disease was carefully investigated at my instance 

 by Mr. G. P. Cliuton, assistant in the botanical department of the University of Illi- 

 nois.:}: Only one fungous form was found attacking the fish — probably the well-known 

 Saprolegnia fercuc. It was not, at the time of his visit, in a stage of development 

 favorable to the precise determination of the species, and there is consequently some 

 uncertainty with respect to its specific name. There is no doubt, however, that it 

 belongs to the genus Saprolegnia. It appears in patches, large or small, either in the 

 form of a grayish or whitish film (sometimes half fluid and sometimes resembling a 

 thickish felt), or as a growth of delicate threads an eighth to half au inch in length, 

 springing from the surface of the affected fish either in tufts or irregularly distributed. 

 It takes its origin in every case in microscopic spores each provided with minute 

 swimming hairs (flagella) by which they move freely through the water. These spores, 

 matured by myriads in growing fungous threads, settle on excrement or dead animal 

 matter in the tank, and may grow and multiply there as freely as on the fish. 



Dead flies furnish an excellent nidus for the cultivation of this fungus, and the 

 presence of the spores in the water may be very easily determined by simply dropping 

 a dead fly into a bottle filled with the water to be tested. In this way we demon- 

 strated the general infection of all the waters in and out of the aquarium. Every 



* All the tanks but two were occupied on " opening day," many of them to the limit of their 

 capacity. 



tin our efforts to control thin fish-parasite, and in matters of aquarium management generally, I 

 enjoyed the great advantage of the aid and advice of Dr. T. II. Bean, representative of the U. S. Fish 

 Commission on the Government Board of Control. His long connection with the Commission in 

 capacities which made him thoroughly acquainted with its aquarium methods, and his own experi- 

 ence while in charge of the aquarium exhibit of the Commission at the Cincinnati Exposition in 1K88, 

 made him an invaluable adviser in every emergency, and much of our success was due to his unfailing 

 kindness and to his warm personal and official interest in aquarium affairs. 



I take this occasion also to express my obligations to Mr. W. de C. Raveuel, chief special agent of 

 the, Commission, in general charge of its exhibit, for much valuable assistance and advice given in his 

 capacity of administrative officer. 



The aquarium was in immediate charge of Messrs. L. (i. Harron and Alexander Jones, without 

 whose expert skill and faithful service success would have been utterly impossible. 



{Mr. Clinton's report is presented as an appendix to this paper. 



