they will stand. A saturated solution of soda is then applied with a 

 paint brush to both sides of the fish, which is immediately thereafter 

 put in the weaker solution of soda. This is very effective in killing the 

 parasites, although difficult to do because they will bury themselves in the 

 mucous membrane. 



Dr. D. L. Belding, Hingham, Mass. : The subject of fish disease is 

 important to the fish culturist because the ultimate and continued success 

 of a hatchery depends in a large measure upon freedom from disease. 

 Fish are subject to diseases of various kinds: nutritional, developmental, 

 parasitic, and bacterial, not to mention mechanical injury, e.g., water 

 pollution. With the exception of a few protozoans, crustaceans, and 

 worms, the parasitic diseases are of minor importance. The fish culturist 

 is chiefly concerned with the bacterial diseases, especially the epidemics 

 which at times threaten to ruin completely his hatchery. I believe that 

 the work of Mr. Hayford, Dr. Foster and Dr. Embody, looking toward 

 the prevention of disease by building up the resistance of the fish by 

 means of proper environment, natural food, and selective breeding, is 

 a most important step towards the prevention of disease in our hatch- 

 eries. However, steps must also be taken to combat diseased directly, 

 since the virulence of the invading organism, as well as the resistance of 

 the fish, must be considered. If you can eliminate the organism or reduce 

 its virulence, you will solve the problem. 



In the summer of 1920, at one of the Massachusetts state hatcheries, 

 we lost our entire stock of fingerling and adult brook trout, owing to 

 an epidemic of the disease commonly known as "Furunculosis," which is 

 caused by a pleomorphic bacillus. Possibly six writers in Europe and the 

 United States have described organisms so similar that I believe we have 

 to deal with a general group, the individual members of which differ in 

 virulence, in type of lesions, and in certain other characteristics. The 

 disease which became epidemic during the summer months first broke 

 out in the previous December, but caused slight mortality during the 

 cold weather. As the temperature of the water taken from a lO-acre 

 pond rose above 55° F., the number of deaths began to increase, and by 

 the time it had reached 60° F. the disease had Become epidemic, spreading 

 from pool to pool, until all the fish were infected. At the height of the 

 epidemic, a death rate of 500 adults per day was attained. If we had 

 been able to keep the temperature of the water below 55° F., this par- 

 ticular disease could never have assumed epidemic proportions. The 

 chances of having epidemics are considerably lessened when the tempera- 

 ture of the water at a hatchery is less than 55° F., even though cold 

 water itself will not entirely eliminate disease. As a rule, the warmer 

 the water, the more difficult is the control of an epidemic, owing to the 

 lowered resistance of the fish and the maximum growing temperature for 

 the bacteria. To illustrate, in Furunculosis, at 57° F., it takes five days 

 to kill inoculated fish, while at 65° F., similarly treated fish die in two 

 days. 



While I shall confine my remarks to only one bacterial disease, 

 Furunculosis, the same general principles hold true for all bacterial dis- 

 eases. Furunculosis is spread chiefly from fish to fish by direct contact, 



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