276 BULLETIN OF THE BUREAU OF FISHERIES. £ 



percentage of cases, provided the gills are not affected. The solution can best be applied 

 by gently swabbing the lesion with a small piece of cotton which has been previously 

 dipped in the solution. Two or three applications at intervals of 6 to 12 hours 

 should be sufficient. After each local application of the copper sulphate the fish should 

 be placed in a 1 to 1,000 solution for one minute. 



Since, in most cases, the disease is primarily due to injuries or weakened vitality 

 the old adage, "An ounce of prevention is worth a pound of cure," is peculiarly appli- 

 cable in this case. Above everthing else, anyone handling fish should exercise the 

 greatest care to prevent injuring the fish in any way. Even the slightest injury, such 

 as the rubbing off of a few scales or even a small portion of the mucous covering, may 

 lead to infection. When taken in a net or seine the delicate caudal fin is very easily 

 injured by the struggles of the captured fish and every effort should be made to reduce 

 the injury to a minimum. A large percentage of infections among fish taken in this way 

 first appear on the caudal fin, and undoubtedly injury to the fins is one of the most 

 common causes of infection. 



Great care should be taken to prevent the spread of the disease through the use 

 of infected nets or vessels. This can be easily prevented, since the bacteria are entirely 

 destroyed by thorough drying for several hours in direct sunlight. 



Finally, in the case of fish confined in aquaria it is essential that *11 infected indi- 

 viduals be removed at once. As in the case of any contagious disease all contact of 

 healthy with diseased individuals should be guarded against. It has been shown that 

 bacteria are continually leaving diseased fish and thus may readily get on any healthy 

 fish in the same aquarium. 



It should be said in passing that this treatment is also very effective for ectoparasitic 

 Protozoa. Experiments on fish infected with Costia, Chilodon, and Cyclochseta have 

 shown that these parasites are entirely destroyed by a single treatment with copper 

 sulphate. In the case of fish infected with Ichthyophthirius the treatment is not so 

 successful, since the encysted stages are not affected. The exposed parasites are, how- 

 ever, entirely destroyed. 



A number of other chemicals have been tried, but none of them has given encour- 

 aging results. Lysol and creolin were found to stop all movements of the bacteria in 

 four to five minutes when diluted 1 to 5,000. The use of such strong solutions is, how- 

 ever, not practicable, since buffalofish and bullheads placed in a 1 to 5,000 solution for 

 1 minute died within 24 hours. Formalin was also found to be of no value for the same 

 reason. 



Since sodium chloride is used a great deal by fish-culturists for fungus a number 

 of infected fish were treated with solutions of various strengths. It was soon found 

 that the bacteria are not appreciably affected by solutions which seriously injure the 

 fish, and it is not believed that this treatment is of any value against the disease. In 

 fact our experiments indicate that it may actually aggravate the disease by weakening 

 the fish. 



ECONOMIC IMPORTANCE OF THE DISEASE. 



At the present time it is impossible to make any general statements regarding the 

 importance of this disease. So far, with the exception of two slightly infected fish at 

 Ogdensburg, N. Y., the disease has been recognized only at Fairport. Here it has caused 



