FISH-CULTURAL PRACTICES IN THE BUREAU OF FISHERIES. 715 



gallons of water per minute at a temperature of about 50°, it is customary to 

 hatch and hold in each trough 50,000 sac fry, 25,000 advanced fry, 12,500 1}^- 

 inch fingerlings, 4,000 i^-inch fingerlings, 2,000 i^-inch fingerlings, and 1,000 

 fish 2 to 3 inches in length. Much larger numbers are often carried under simi- 

 lar conditions without serious loss, though often with the result that the fish 

 prove weak in transportation. 



At stations where the facilities permit, a congested condition of the hatch- 

 ing troughs is avoided by transferring some of the fish to outdoor ponds as soon 

 as they have learned to take food readily, or, if weather conditions are suitable, 

 after being fed two or three weeks. In rearing fingerlings for four to six months, 

 concrete ponds 18 to 25 feet in length by 5 to 6 feet in width and 2^ feet deep, 

 with a fall of 8 to 10 inches in the bottom for drainage, give good results at the 

 Manchester (Iowa) station. The stock ponds at Manchester, 76 feet long, 17 

 feet wide, and 3 feet deep, supplied with 40 gallons of water per minute 

 at a temperature of 50° to 60°, have a capacity for 3,500 rainbow trout 2 years 

 of age; 1,800, 3 years old; 1,000, 4 years old. and 900, 5 years old. This 

 trough and pond system is typical for rearing any species of brook trout, as 

 well as lake trout and Atlantic and landlocked salmons, for three or four 

 months, which is as long as it is customary to hold young fish intended for dis- 

 tribution. Brood fish may be obtained by selection from the fingerlings 

 intended for distribution, which as they develop are transferred to stock ponds. 



As soon as the fry swim up looking for food they are fed several times a 

 day an emulsion of finely ground liver. This diet is continued as the young fish 

 develop, with the difference that the liver is less finely ground and is given less 

 frequently — two or three times a day being sufficient when the fish have attained 

 a length of 2 or 3 inches. The kind of liver used varies at different stations, 

 that of sheep, beeves, and hogs being extensively used, and the relative value 

 of each being in the order named. The food for the larger fish consists of the 

 liver, Itmgs, and hearts of the animals already mentioned. 



At Manchester, Iowa, it has been found advantageous from an economical 

 standpoint to mix the animal food, after it has been ground, with a mush made 

 by cooking wheat middlings or shorts, to which a moderate amount of salt is 

 usually added. After the mush has been thoroughly cooled the animal matter, 

 uncooked, is stirred into it in the following proportions: For fingerlings, i part 

 animal matter and 2 parts mush; for adults, i part animal matter and 3 parts 

 mush. Twenty gallons of boiling water and 50 pounds of wheat middlings will 

 make about 202 pounds of mush. 



The provision of food for domesticated fish is one of the greatest problems 

 the fish culturist encounters, and has been the subject of considerable experi- 

 mentation. The intensive production of natural food has not received in the 

 United States so much attention as in Europe nor so much as the subject 



