7l6 BULLETIN OP THE BUREAU OF FISHERIES. 



deserves. The American method of raising trout precludes the economic use of 

 natural live food, although unquestionably the edible qualities of the fish might 

 be much improved thereby. 



For several years the roe of the branch herring {Pomolobus pseiidoharengus) 

 has been used at several stations as a substitute for liver in feeding fry and 

 fingerlings. It is purchased from cannery men, who preserve in tins large quan- 

 tities of it for human consumption, and consequently are able to sell it at a price 

 close to or less than the cost of liver, due allowance being made for the waste 

 in liver and the labor involved in its preparation as a fish food. The herring 

 roe has the advantage of always being on hand in condition ready to feed and is 

 therefore especially desirable for isolated stations. It is not customary to feed 

 young fishes on this food after they are 2 or 3 months old. 



At Craig Brook, Me., fly larvae," used for a number of years in rearing 

 trout and salmon to fingerlings, proved to be a very satisfactory food and the 

 fish attained a more rapid growth than when fed on liver and other dead material. 

 From a financial standpoint it was not as economical as freshly prepared liver 

 or other animal foods, and this, coupled with the objectionable odor attendant 

 on its preparation, had much to do with its discontinuance. 



It is possible, however, to utilize animal refuse advantageously for the pro- 

 duction of fly larvae by means of a contrivance in which the material on which 

 flies have deposited their eggs may be suspended over the water. This con- 

 trivance consists of a wooden frame, like a box without top or bottom, placed 

 on floats and having an air-tight cover to prevent the escape of foul odors. 

 Within the frame are two trays, the bottoms of which are made of coarse 

 wire cloth (odds and ends of old hatching trays). Excelsior or straw is placed 

 on the trays, and waste meat or other animal refuse is placed on top of this 

 material. As the larvae hatch they work through the excelsior, cleaning them- 

 selves thereby, and drop into the water. Two small trays are preferable to one 

 of larger size, that the meat may alternately be renewed, thus insuring a more 

 constant supply of larvae. The noxious animals killed in the protection of fish 

 may advantageously be disposed of in these trays. 



SPECI.\L DEVICES APPLIED AT TROUT STATIONS. 



Study and experience in recent years have revealed abnormal aeration as 

 a condition existing in various water supplies at trout-culture stations, with 

 consequent mortality among the fish. Of the methods used to correct such 

 abnormalities, that devised by the superintendent of the station at White 

 Sulphur Springs, W. Va., Mr. R. K. Robinson, has proved the most efficient. 



" Atkins, X^has. G. : The live food problem, American Fisheries Society, 1903; also Food for young 

 salraonoids, Proceedings Fourth International Fishery Congress, Bulletin Bureau of Fisheries, vol. 

 xxviii, 1908, p. 839-851. 



