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 

 (Myxobolus) 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 Myjcosporidia from the ulcers can not of 

 course be stopped entirely, but it is evident that it will be less if all fishermen are impressed with 

 the importance of destroying all diseased and dead fish instead of throwing them back into the water. 

 Such destruction must be 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.i 



Representatives of this order are numerous among the parasites of fishes, but, so 

 far as I 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 uuinfected 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 Diplostomum cuticola) was found in great 

 abundance on the viscera of three species of sunfish, Lepomis aitritw, Ghasnobryttu* 

 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 j Noa. 17, 18, and 19. 



