MANUAL OF FISH-CULTURE. Ill 



or if it aboiiuds with aquatic insects, it is quite esseutial to have some 

 kind of filtration, otherwise the eggs may be injured by animalculse 

 or coated with sediment, the trays clogged with refuse, the circulation 

 stopped, and in the end a majority of the eggs lost. Many filters 

 have been devised, all of which are good, but a simple and effective 

 contrivance is made by tacking medium-weight flannel to wooden tray 

 frames and placing them at the head of the tank directly beneath the 

 head of water, the number used at one point being governed by the 

 amount of sediment or other foreign matter j)resent. 



At Northville, as a convenience in caring for eggs, a shallow "picking- 

 trough" is used, 40 feet long, 10 inches wide, and 2^ inches deep, with 

 a t}-inch strip, § of an inch wide, nailed along each side of the bottom, 

 upon which the trays rest, to give a good circulation while the eggs are 

 sorted over*. The trough has a fall of not more than ^ inch throughout 

 its entire length, and it is fed by a flow of about 2 gallons of water 

 per minute. A dam at its lower end raises the water 1^ inches, not 

 entirely covering the trays. This is a point that must not be over- 

 looked, for if the water flows over the tops of the trays many of the 

 eggs and fry will be apt to escape through the waste-pipe. 



CARE OF THE EGGS AND FRY. 



Upon their arrival at the hatchery the eggs are taken from the 

 shipping-cases and turned into tubs, whence they are removed to the 

 hatching-troughs. In removing eggs from the flannel shipping trays 

 to the tub the same method is followed as in washing eggs that have 

 been held in cases for several days. The transfer should take place in 

 a temperature not higher than 45° or 50° F., and if the eggs are held 

 in the tubs for any length of time they are given a change of water 

 every 30 minutes. 



Great care is necessary in transferring eggs to the hatching-trough 

 in pails. To guard against any shock, the pail is partially filled with 

 water, and the eggs are carefully taken in the dipper, which is lowered 

 into the pail in such a way that the eggs will glide into the water and not 

 fall upon it. The pail when filled is placed upon the trough as near as 

 possible to the box for which the eggs are intended, and by means of a 

 perforated dipper with a capacity of 20 ounces, or 4,000 eggs, they are 

 transferred to the hatching-boxes. A tray is placed in the water and 

 one dipi)erful poured upon it, whereupon a second tray, placed on top 

 of the first, is served in like manner, and this is repeated until ten trays 

 are filled. The eleventh, or cover tray, is left empty, and the whole 

 apparatus is held in place with a crossbar or binder. In two double 

 troughs, containing G4 boxes and occupying a floor space of 100 square 

 feet, 2,560,000 eggs may be safely carried with 22 gallons per minute 

 of good spring or lake water, well aerated. 



To estimate the number of eggs laid down, a fractional portion of a 

 quart is counted several times until a satisfactory average i.^ arrived at; 

 this has given 200 to the ilnid ounce, or 0,400 to the quart. 



