56 NEW YORK AQUARIUM NATURE SERIES 



their functioning. This disease is known among fish breeders as 

 '"tuberculosis." The *'red disease" of the skin of goldfish, ide and 

 other cyprinid fishes is also bacterial in origin. The weaker per- 

 manganate solution and a 2% solution of common salt have been 

 used with some success in the treatment of these diseases. What 

 part bacteria play in causing internal diseases of fishes is but 

 little known, although diseases of the liver and other internal 

 organs have been ascribed to this cause. 



A^iimal Parasites. — Apparently these are much more nu- 

 merous in species than are the plant parasites and they belong to 

 several classes. Among the larger ones may be mentioned the 

 leeches, crustacean parasites or fish-lice and worms (tape-worm, 

 treinatode and round-worm) . External parasites, if large, ordi- 

 narily give but little trouble as they may be readily removed with 

 fine tweezers. 



Minute species of trematodes or fluke-worms (Gyrodactylus, 

 etc.), are sources of great loss, at times causing the death of 

 whole schools of goldfish. These tiny parasites are almost mi- 

 croscopic, but can readily be seen with an ordinary lens. On 

 young fish they may be found all over the body and even in older 

 specimens they may occur in such numbers upon the skin that 

 they produce serious sores, but adult specimens are more fre- 

 quently injured by attacks on the gills. Sal ammoniac in one- 

 half per cent, solution, common salt in two per cent, solution, and 

 potassium permanganate in the weaker solution, say one part to 

 10,000 are all recommended for treatment. However, when the 

 parasites attack the gills in large numbers it is practically im- 

 possible to effect a cure, as any treatment fatal to the parasites is 

 likely also to prove fatal to the fish. 



Internal parasites, as a rule, cannot be diagnosed, but they 

 seldom cause much trouble among aquarium fishes. To be sure 

 many forms of parasitic worms have been described as inhabit- 

 ing the intestinal tract or embedded in the flesh. But even if it 

 were possible to diagnose these cases in life, it would probably 

 be impossible to eflfect any cures. 



A number of species of unicellular parasites (Protozoa) at- 

 tack the skin of various fishes in the aquarium. Usually the 

 presence of the parasites becomes evident to the naked eye as 

 minute whitish flecks or protuberances on the skin. The fish 

 becomes languid in its movements, refuses to take food and 

 breathes rapidly in a labored manner. Two of the better known 

 of these parasites, Costia and Chilodon, attack the skin exter- 



