NATIONAL FISHERY CONGRESS. 
195 
PROTOZOA. 
Parasitism occasioned by the presence of one-celled organisms has not been much 
studied in this country. Gurley’s paper (No. 5) is an admirable compilation, and, it is 
to be hoped, will be followed by systematic work on the psorosperms of fishes inhabit- 
ing American waters. From an economic point of view, it is probable that parasitism 
which results from infection with protozoan parasites will, of all kinds, be found to be 
most important. Epidemics among European fish have been repeatedly traced to this 
source. The fatality which attends infection with psorosperms appears to be due to 
a secondary cause, however, namely, to bacilli which develop within the psorosperms 
(Myxobohis) tumors and give rise to ulceration. The discharge of these ulcers then 
disseminates the disease. For an account of an epidemic among barbels in the Meuse 
and other rivers of France and Germany, see Gurley’s paper (No. 5), p. 231. 
Brief mention of the remedies there proposed, pp. 233-234, may appropriately be 
repeated here. Megnin sees no other method than to collect all the dead or sick 
fishes and destroy them by fire. Ludwig thinks that the waters should be kept pure 
and that the pollutions of the rivers by communities or industrial establishments 
should be interdicted. Further he says : 
That most dangerous contamination of the water by the Hyxosporidia from the ulcers can not of 
course he stopped entirely, hut it is evident that it will he less if all fishermen are impressed with 
the importance of destroying all diseased and dead fish instead of throwing them hack into the water. 
Such destruction must he so effected as to prevent the reentry of the germs into the water. 
Kailliet says that it is expedient to collect the diseased fish and to bury them at a 
certain depth and at a great distance from the water-course. He further states that 
this was done on the Meuse with success, so that at the end of some years the 
disease appeared to have left no trace. 
TREMATODA . 1 
Representatives of this order are numerous among the parasites of fishes, but, so 
far as 1 have observed, are not likely to occur in sufficient numbers to occasion serious 
loss. Their presence will be a tax, nevertheless, on the vitality of their host, which 
may be, in many contingencies, the determining factor in causing that host to fall an 
easier prey to its pursuer than its uninfected comrade will do. 
In my paper on Trematodes, No. 17 of the appended list, are described 31 distinct 
species and one variety taken from 25 specifically distinct hosts. In the majority of 
cases these worms were found in small numbers in the intestines of their hosts, and 
presumably occasioned little inconvenience. In a few cases, however, I found them 
encapsuled in various positions in the body cavity, and occasionally in such numbers 
that they must have affected seriously the vitality of their hosts. For example, a 
species (which was referred to Diesing’s JDiplostomum cuticola ) was found in great 
abundance on the viscera of three species of sunfish, Lepomis auritus, Chcenobryttus 
gulosus , and, probably, Lepomis pallidus. The viscera consisted mainly of hearts and 
livers, and were sent to me by Mr. N. A. Harvey, of Kansas City, Mo., January, 1894. 
The serous coats of these organs were thickly studded with cysts. These were very 
numerous, and varied in size from minute specks to capsules measuring over 1 mm. in 
diameter. The largest larva, upon removal from its cyst, measured, in alcohol, a little 
over 1 mm. in length and about 0.4 mm. in breadth. On account of the immense 
numbers of these parasites they might very easily prove to be an economic factor of 
1 See List of Authorities : No. 6 and 13, pp. 553, 554, pi. 65, figs. 22-30; Nos. 17, 18, and 19. 
