and are bandied the same, is one of the problems we are attempting to 

 solve. 



Generally speaking, we can correct excess mortality by substituting 

 for meat such natural insect foods as fly maggots, the larva of the Culex 

 mosquito, and the fresh-water sow bug. I would like to emphasize the fact 

 that when the meat diet is stopped and natural food is substituted the 

 affected fish live a great deal longer and a large proportion of them re- 

 cover. Three or four other hatcheries have obtained practically the same 

 results. It is noticeable that when we place affected fish in natural 

 streams where they secure insect food a large proportion immediately 

 recover. 



We have found that fish flesh and intestines are more attractive to 

 flies than other flesh, such as sheep liver and lungs, and that, if the 

 weather conditions are the same, a given amount of flesh distributed in 

 numerous small quantities over a large area will produce more maggots 

 than the same amount placed in one spot. The mosquito larvae are secured 

 by pond fertilization with skimmed milk, according to the method which 

 Dr. Embody has explained in a paper at this meeting. The sow bug or 

 Asellus is developed in a stream which is choked with water cress and 

 Elodea canadensis, and which receives the washings and waste water 

 from the trout ponds. It is estimated that 100 bushels of these bugs 

 were secured from this stream during the summer of 1921. About 150 

 tons of fish food of all kinds is used at the hatchery each year. A daily 

 record of the mortality of each individual pond is charted and a glance 

 shows when the mortality of any particular pond is rising. One instance 

 of the value of our chart method was a spring fed pond which supplied 

 some trout ponds, but the water did not produce the same results as were 

 secured by using water from other spring fed ponds. This year the spring 

 was enlarged and deepened, and aquatic plants and insects were placed 

 in the ponds, which now are among our most successful for raising trout. 



Mb. G. C. Leach, Washington, D. C. : Do I understand that the para- 

 site IchthyoptMrius has given you considerable trouble at Hackettstown? 



Mr. Hayfobd : No, it has not. Most of our water has a temperature 

 of about 50°, at which the parasite causes no trouble. Rainbow trout, 

 however, need a temperature of from 60° to 65° and at this temperature 

 the disease becomes serious. We have found a method of eradication 

 which consists simply of placing the affected fish in a pond with a strong 

 flow of water. Since the parasite must leave the body of the fish to 

 propagate, it is at once swept away by the water. The ponds from which 

 the fish have been taken are treated with a one per cent solution of 

 milk lime. We have always been able to confine this trouble to one pond, 

 and since the foregoing method was tried have had no further outbreaks. 



Mr. Leach : In our aquarium at Washington we have trouble with 

 the parasite Ichthyopthirius every spring, when the temperature of the 

 river water gets above 50° F. At that temperature or below the growth of 

 the parasite is arrested. The trouble continues until the temperature rises 

 to about 65°, and then it disappears. We have never treated fish with 

 a lime solution, though we have tried common baking soda. We put the 

 fish in a trough containing about as strong a solution of the soda as 



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