CXXIV REPOET OF COMMISSIONER OF FISH AND FISHERIES. 



to a large number of fishes, young quiunat salmon and young Swiss 

 lake trout being the S]>ecies chiefly affected. The disease in its appear- 

 ances and symptoms differed from any previously manifesting itself in 

 the local aquaria, and on examination was found to be due to a proto- 

 zoan parasite {Ichtliyo'phthirius mulUfiliis Fouquet). This is the same 

 animal that produced great mortality among fishes in the Fish Commis- 

 sion aquaria at the World's Columbian Exposition in 1893, and was 

 there studied by Dr. Stiles, of the Department of Agriculture, whose 

 report on the subject is printed in the Bulletin of the Commission for 

 that year. It is noteworthy that at Chicago Xha disease first appeared 

 in a lot of catfish [Ameiurus alhidus) from the Potomac Eiver. 



The parasite thickly covers the entire surface of the body and also 

 enters the mouth and gill-cavities and the intestines. The skin becomes 

 coated with a thick mucus, the gills are matted together with slime, 

 and the gill-coverings bulge. The infested fish abstain from eating and 

 remain at or near the surface of the water. The respiratory movements 

 are rapid and gasping. Death is gradual and seems due to a combina- 

 tion of starvation and asphyxiation. 



From GO to 70 per cent of the salmon and nearly all of the trout 

 succumbed to the disease, which was arrested in the course of a month 

 by thoroughly cleaning the aquaria and filling them with a strong salt 

 solution. About the first of May some of the young salmon were 

 sent from Washington to the aquaria at the Nashville Exposition. In 

 a few weeks the disease appeared on them, but they were killed before 

 the trouble had spread to other fishes. Brook trout in the same aqua- 

 rium were not attacked. 



In the spring of 1897 a diving beetle {Laccophilus maculosus) appeared 

 in numbers in the fish ponds in Washington and proved destructive to 

 young bass. Dr. H. F. Moore made some observations on its habits 

 and ravages, and found it to be a very dangerous enemy of young fish, 

 which it attacks savagely. Beetles in the larval stage were also dis- 

 covered in the bass ponds. Suggestions were made as to expedients 

 for preventing subsequent inroads on the young bass. 



