12 TJ. S. BUREAU OF TISHEEIES. 



minimum is as low as 3 inches, but only under circumstances in otlier 

 respects extremely favorable will this answer the purpose, and then 

 it is permissible only where there is an ample supply of aerated 

 water, where the hatching troughs are less than standard in length, 

 and where there is no danger of inundation. One disadvantage of 

 a 3-inch fall is the impracticability of utilizing any form of aerating 

 apparatus ; another is the necessity of placing the troughs below the 

 level of the hatchery floor. This makes the work of attending the 

 fish and eggs very laborious. A fall of 1 foot will do fairly well if 

 there is entire safety from inundation, as then the troughs may bo 

 placed on the floor, which is better than below it though still in- 

 convenient, and some of the simpler aerating devices can be intro- 

 duced. A fall of 3 feet is better, but a 10-foot fall is much better still 

 as it permits the placing of tha lowest hatching troughs 3 feet above 

 the floor and leaves ample room for complete aeration. Everything 

 depends upon the volume and character of the water, however, and 

 upon its aeration before reaching the hatchery. In a small estab- 

 lishment there is no necessity for additional aeration in the building, 

 and therefore a 3-foot fall is adequate. 



Insj^ection of the site during flood season will suggest the safe- 

 guards necessary to provide against inundation. If located by the 

 side of a brook, the building should not obtrude too much on the 

 channel, and below it there should be ample outlet for everything 

 that may come in the way of floods or freshets. Often much can be 

 done to improve a poor site by clearing out and enlarging a natural 

 watercourse. In a cold climate it is an excellent plan to have 

 the building partly under groimd for greater protection against 

 cold. When spring water is used, there is rarely any trouble from 

 the formation of ice in the troughs, even in a cold building, but 

 in the latitude of the northern tier of States the water from lakes, 

 rivers, or brooks is so cold in winter that if the air of the hatchery is 

 allowed to remain much below the freezing point ice will form in the 

 troughs and on the floor to such an extent as to be a serious annoy- 

 ance. In very cold climates stoves are needed to warm the air suffi- 

 ciently for the comfort of the attendants, but the building should 

 be so located and constructed that it may be left without a fire for 

 weeks without any dangerous accumulation of ice, and if the site 

 does not permit of building the house partly under ground, the 

 walls must be thoroughly constructed and well banked with earth, 

 sawdust, or other material. In warmer climates no trouble will be 

 experienced from that source. The type of building will, of course, 

 be governed by the exigencies of each individual case. The location 

 selected, extent and character of the fish-cultural work proposed, and 

 the funds available, are all to be considered. The foregoing sug- 

 gestions would apply to a small establishment in a more or loss re- 

 mote section and where strict economy in construction and operation 

 are important. 



DAMS. 



The required head of water can often be obtained by throwing 

 a dam across a stream and locating the hatchery near by. The dam 

 will cause a small pond to form, serving the double purpose of 

 aerating and settling the water. Unless the bed and the banks of 

 the stream are of such character as to insure safety from under- 



