ARTIFICIAL. PROPAGATION OF TROUT. 47 



The riffle ponds, 50 feet long by 5 feet wide (fig. 16, p. 48), 

 carrying 40,000 No. 1 fingerling fish, receive from 20 to 40 gallons 

 of water per minute. Yearlings and older fish in the brood or rear- 

 ing ponds receive from 200 to 500 gallons of water per minute. A 

 strong current of water is desirable in both the troughs and ponds, 

 as it necessitates constant activity on the part of the fish, producing 

 stronger fish than can be obtained in more sluggish water. The 

 volume of water given here for fingerlings No. 1 and larger may be 

 reduced without material disadvantage if the water temperature 

 does not exceed 54°, but where water is plentiful and there is no need 

 to economize in its use the amounts given can be used advantage- 

 ously. In rearing ponds more water is required, as the circulation 

 is not so good, and the outdoor exposure causes the temperature of 

 the water to rise. 



CARE OF EGGS AND FRY. 



After the eggs are placed on the trays the only attention neces- 

 sary until hatching begins is to keep them clean; dead eggs, which 

 may be known by their turning white, must be picked out at least 

 once each day. After the eyespot is plainly visible it is well to run 

 a feather through the eggs for the purpose of changing their posi- 

 tion on the trays and to disclose any dead eggs or foreign matter 

 that may be hidden underneath. The greatest care should be exer- 

 cised in handling the eggs at any time to avoid injuring them, 

 esiDecially from the first or second day after collection until the eye- 

 spots appear, and then only when absolutely necessary. During this 

 period the eggs are very delicate and they should not be disturbed 

 except to carefull}- remove the dead ones. This may be accomplished 

 with wooden or metallic tweezers. A moderate amount of sediment 

 has no harmful effect, since it covers one side of the eggs only. In 

 cases where sediment is deposited on the eggs in sufficient quantity 

 to solidify the mass and thus impair water circulation, the tray may 

 be shaken gently, keeping the eggs well submerged during the opera- 

 tion. 



In a water temperature of 53° the eyespots appear in about 13 days 

 and at this time the eggs should be feathered carefully. In water 

 of this temperature hatching occurs in from 35 to 38 days. A higher 

 temperature shortens the incubation period, while a lower tempera- 

 ture lengthens it. As a rule, the best results are obtained in tem- 

 peratures from 48 to 54°. A lower temperature prolongs the in- 

 cubation period unduly, while higher temperature encourages the 

 growth of fungus. 



After the fry hatch they require but little attention until the um- 

 bilical sac is absorbed and the time for feeding arrives. They are 

 examined daily and the dead fish and decayed matter removed from 

 the troughs, which must be kept perfectly clean to keep the fish 

 in healthy condition. As the fish grow they should be thinned out 

 in the troughs from time to time as their size may require. When 

 tliey first begin to feed, 20,000 to 25,000 fish per trough are not too 

 many, but when they have attained a length of 1^ inches the number 

 should be reduced to not more than 15,000, while from 3,000 to 4,000 

 three-inch fish are as many as one trough will accommodate advan- 



61976°— 23 4 



