PROGRESS IX BIOLOGICAL IXQUIKIES, 1921, 27 



less than half a millimeter in length, and so translucent that one 

 may easily overlook them. 



Some bullheads removed from a quarry pond near the Mississippi 

 Eiver died within 24: hours after being placed in an aquarium of 

 running water. The earl}- death of these usuall}^ most hardy fish 

 could be explained only on the supposition that their vitality had 

 been greatly diminished by tlie small and abundant trematodes 

 (Gyrodactylus) scattered over the entire surface of the body. Pos- 

 sibly many fish in the river are unfavorably affected by these worms. 



Dr. Van Cleave found a species of another genus of parasitic flat- 

 worms upon the gills of sunfish, black bass, and channel catfish, but 

 it is believed that worms of this genus (Ancyrocephalus) do not 

 cause dangerous infestations. 



Very little study has been devoted to the ectoparasitic flatworms 

 on this continent, and previously but four species have been reported 

 from fresh-water fishes. Much attention has been given them in 

 connection with fish culture in Europe. Treatments which European 

 writers have recommended are: (1) A one-fourth of 1 per cent solu- 

 tion of salicylic acid, in which the fish remains half an hour (Hiibner) ; 

 and (2) a solution of 1 part of i)otas«ium permanganate to 100,000 

 parts of water. The treatments may require modification for our 

 species of fish and of parasites. 



Dr. Van Cleave has also described a new genus of trematodes based 

 upon specimens taken from tlie white bass. Roccus chrysops^ collected 

 in Iowa, Illinois, and Minnesota. The parasites were found only in 

 the digestive tract and at present are ascribed no economic signifi- 

 cance. The parasites are not found in Morone inferriipfa, although 

 that species is a close relative of the white bass. He finds, indeed, 

 tliat the trematode parasites of tbe yellow l)ass are entirely distinct 

 from those of the white bass, although the two related species display 

 marked similarity in range, local preference, feeding habits, and 

 food. 



TKKATMKXT OF ICHTII Voi'IITII IKIUS DISEASE. 



One of the most troublesome external parasitic affections of fresh- 

 water fishes in aijuaria and ponds is (hie to a microscopic protozoan 

 (Ichthyophthirius), which becomes embedded in the skin and sets 

 up a violent irritation. II. L. Canfield, sujierintendent of fish culture 

 at the Fairport station, who has conducted experiments in the treat- 

 ment of channel catfish heavily infected with tlie protozoan parasite, 

 reports that commercial rai-bonate of soda in the form of sal soda 

 (washing soda) is effective in alleviating the trouble. 



Using a receptacle other than metal to hold the solution, 150 g. of 

 sal soda are placed in 4,000 c. c. of water, in which solution the affected 

 fish are dipped. The diseased fish are held in troughs of lively run- 

 ning water, which aids in the treatment and facilitates handling. 

 Before each treatment the fish are forced to the lower half of the 

 trough, where they are separated from the upper half by means of a 

 cross screen. The diseased fish are caught in a hand net, immersed in 

 the solution until they show signs of discomfort (darting about), and 

 then placed in the fresh water at the upper end of the trough. This 

 process is continued until a material reduction in parasites is noticed 



