30 tr. S. BUREAU OF FISHERIES. 



will accommodate 10,000 yearlings, 5,000 2-year-olds, and about 3,000 

 from 3 to 5 years old, though much better results will be attained 

 with half this number. The water supply should be from 100 to 150 

 gallons per minute. For adult fish the pond may be any size from 

 1 acre up to 20 acres or more, provided it has a very large water sup- 

 ply entering at one end and flowing through its longest dimension 

 to an outlet. A 20-acre pond should have a flow of 5,000 to 10,000 

 gallons of water per minute for best results, A raceway or channel 

 should be arranged where the water enters the pond, with a trap to 

 catch the spawning fish as they try to ascend the stream. 



Less care is required in the preparation of food for adult trout. 

 It may be given to them in pieces half an inch in diameter, may con- 

 sist of almost any kind of raw meat or fish, and the flesh may be 

 mixed with cooked mush made of a low grade of flour. Meat meal 

 and fish meal in combination with meat and flour also have been used 

 successfully. 



DISTRIBUTION OF FINGERLINGS. 



Fish which have attained a length of 1 inch are termed "finger- 

 lings No. 1"; those which are 1^ inches long are designated as 

 "fingerlings No. 1^", and so on. Small fingerlings are distributed 

 from the eastern hatcheries in May and June and at a later period 

 in the west. Larger fingerlings are sent out in the autumn. As- 

 signments of fingerling fish are necessarily much smaller than as- 

 signments of fry. In shipping fingerlings No. 1 to No. 2 the num- 

 ber carried in a can ranges from 500 to 1,000, the actual number 

 varying with weather conditions and the length of the trip to be 

 made. Not over 200 No. 3 fingerlings can be safely carried in a 10- 

 gallon can, even under the most favorable conditions. 



EGGS FROM COMMERCIAL HATCHERIES. 



The collections of brook-trout spawn from wild fish, even when 

 supplemented by eggs taken from brood fish under domestication, are 

 totally inadequate to meet the present demand for eggs of that 

 species, and but for the supply resulting from the raising of trout 

 for the market by commercial fish-culturists the production of this 

 fish would be curtailed considerably. The business of growing trout 

 for the market was undertaken in this country more than half a 

 century ago, but within the past 20 years it has developed so rapidly 

 that it is now an industry of considerable importance. 



The main object of the private hatchery usually is the production 

 of adult trout. The eggs, which, as a rule, are stripped from the 

 fish just prior to marketing, are a secondary consideration. As 

 New York and Boston are the best markets for the fish, it is natural 

 that the most successful commercial hatcheries in the east should be 

 located within easy reach of those cities. 



The methods followed by private plants in handling eggs and 

 fry during the early stages of development do not differ materially 

 from those employed at the Federal and State hatcheries. As the 

 end in view is not the same, however, there is necessarily some 

 variation in the treatment of the fish beyond the fry stage. 



At some of the commercial establishments ponds more or less ir- 

 regular in size and shape are used for rearing, but, as a rule, the 

 gi^owing fish are held in long narrow raceways, some of them half 



