KEPOKT OF THE COMMISSIONER OF FISHERIES XXIII 



is to be efficiently done, and in nearly every case a knowledge of the 

 life histories of the fishes involved is important. In hatchery opera- 

 tions also it is necessary to know the proper treatment for the vari- 

 ous diseases that frequently cause great mortality and what consti- 

 tutes the best composition for the artificial foods that must be used. 

 Such investigations are carried on by the staff of the division of 

 scientific inquiry. 



During the past year several fish parasites that have caused serious 

 losses in many of the hatcheries were investigated. A study of 

 Oetomitus salmonis^ a microscopic organism infesting trout, has 

 been completed and a report thereon has been published. This para- 

 site is so common that in some hatcheries it is hard to find trout less 

 than 1 year old that do not contain considerable numbers in their 

 intestines. The manner in which the disease is transmitted has been 

 worked out, and methods that will doubtless do much to reduce the 

 mortality caused by it have been prescribed. 



A study of the importance of vitamines in the dietary of arti- 

 ficially reared fishes was continued, and the results were in com- 

 plete accord with those obtained during 1923. It was found that 

 the addition of cod-liver oil and yeast to beef heart noticeably 

 increased growth and decreased mortality. Beneficial results could 

 be obtained as readily with small amounts of the dietary acces- 

 sories as with larger amounts. In many instances the mortality 

 of fish fed a ration of heart to which a small amount of oil and 

 yeast had been added was less than half as great as among those 

 reared under identical conditions but without the addition of these 

 items to the diet. Results VN^ere not so apparent in the case of fish 

 fed liver, presumably becaus:^ liver is much richer in vitamines 

 than was formerly thought to be the case. 



At the Fairport biological laboratory experiments were continued 

 in the artificial propagation of the sturgeon, sheepshead, silver carp, 

 and paddlefish. Many data have been obtained but progress has 

 necessarily been slow, due to the lack of adequate information on 

 the life histories of these species. The " farm pond " was continued 

 as in previous j^ears and a comprehensive study of pond ecology has 

 been planned, which it is hoped will provide information of value 

 in the development of methods whereby small ponds may be made 

 productive of fish for food. 



During the past j^ear arrangements were made for the utilization 

 of the Holden (Vt.) fish-cultural station for investigations and ex- 

 periments dealing with hatchery problems. The need for such an 

 experimental station has long been felt, as there are many impor- 

 tant problems to solve in connection with artificial propagation. 

 In connection Avith the experimental work at Holden it is planned 

 to conduct field investigations, for which the numerous trout streams 

 in the vicinity afford an excellent opportunity. This work will be 

 undertaken with the cooperation of the State department of fish 

 and game, the officers of which have offered to assist the bureau in 

 every possible way. 



MOSQUITO CONTROL BY MEANS OF FISH 



The prevalence of malaria in the Southern States annually causes, 

 directly and indirectly, many deaths and much suffering. It is also 

 responsible for a marked degree of inefficiency among those affected. 



