MANUAL OF FISH-CULTURE. 43 



elapse between the cleanings. The wire — even galvanized — rusts out 

 in two or three years, and lately the coarser screens have been made 

 of slender rods of oak, which will undoubtedly prove more durable. 



None of the filters described will intercept the finest sediment, and 

 the water is finally passed through a capacious wooden reservoir, 30 

 feet long, 8 feet wide, and 5i feet deep, before it reaches the troughs. 

 This answers the purpose well for the amount of water supplied by the 

 filter last described (about 500 gallons per minute) and is regarded as 

 well worth having, though even this will not insure limpidity in the 

 water when the brook is swollen by rains. 



It may be mentioned that this reservoir is kept brimful at all times, 

 so that all portions of the woodwork, except the railing surrounding it, 

 are kept continuously wet and thus insured against decay for a very 

 long period of years. 



CRAIG BROOK HATCHERY AND ITS EQUIPMENT. 



The Craig Brook hatchery derives its water supply from the brook, 

 which has its source in Craig Pond, but which receives in the lower 

 part of its course many copious springs. This spring water has some 

 advantages, but possesses the serious disadvantage of such high tem- 

 perature in winter as to unduly hasten the development of the eggs, 

 causing them to hatch early and necessitating shipments of eggs in 

 December. 



Accordingly, an aqueduct from a point on the brook above the springs 

 brings to the hatchery a supply of cold water for winter use, in which 

 eggs taken the first of November will not hatch until the following 

 April. This is important, as, if the product of the season's hatching is 

 to be liberated as fry, the late date of hatching will bring them to the 

 feeding stage about the time when suitable food abounds in open waters, 

 and if they are to be reared it is well to shorten up the sac stage and 

 to have the early feeding stage fall at a date when the temperature of 

 the water is rapidly rising, which will get the fish (|uickly through 

 that most difficult of all stages of growth. 



The aqueduct is about 1,600 feet long, with a bore 4^ inches, and has 

 a nearly uniform descent and total freedom from depressions, and is 

 from end to end one single piece of cement concrete. It delivers to the 

 hatchery about 100 gallons of water per minute, which is sufficient for 

 the development of 4,000,000 eggs, and possibly many more. It was 

 built in place around a slightly tapering core, which was drawn forward 

 as fast as the mortar set, and it has now done good service for seven- 

 teen years. By this means the temperature of the hatchery water is 

 maintained 3^ below that of the brook modified by the springs. During 

 the five months from November 1, 1895, to April 1, 1896, the mean tem- 

 perature in the hatchery was 36.65"^ F. 



