AKTIFICIAL PROPAGATION OF TROUT. 17 



advantages for aeration over a closed pipe. For a hatchery containing 

 20 hatching troughs a supply trough 10 inches wide by 10 inches deep, 

 inside measurements, will carry sufficient water. As it enters this in- 

 side supply trough from the main conduit the water should have as 

 great a fall as possible, and a number of riffles throughout its length will 

 aid aeration further. The hatching troughs should, if possible, be 

 set some 6 inches lower than and 3 to 4 inches distant from the 

 supply trough. A satisfactory method of regulating the flow of 

 water to the hatching troughs is by means of a 2-inch brass-faced 

 molasses gate, set about 3 inches above the bottom of the supply 

 trough. The horizontal screens and blocks on which the water falls 

 as it leaves the supply trough, mentioned in connection with the 

 propagation of rainbow trout, are recommended. The same results 

 may be obtained by causing the water to pass through a pan (a 

 6-quart size is satisfactory) with a perforated bottom before entering 

 the hatching trough or through a series of such pans in a rack one 

 above the other, spaced a few inches apart. In cases where the 

 water from a hatching trough is used again in troughs at a lower 

 -level one of these or a similar device is desirable. 



In most instances, temperature and other conditions being equal, 

 the more perfect the aeration the smaller the volume of water re- 

 quired, and, conversely, the greater the volume the less aeration is 

 needed. In any event exposure to the atmosphere under the condi- 

 tions mentioned can not result harmfully, and it may be very bene- 

 ficial to water from any source intended for fish-cultural purposes. 

 The use of all practicable means of aeration is recommended. 



HATCHERY EQUIPMENT. 



The troughs and other equipment used in the incubation of trout 

 eggs vary considerably as to dimensions. All of the various kinds 

 in general use have meritorious features, and in many instances they 

 were designed to meet peculiar local requirements. The general 

 principle in each case remains the same. The eggs are placed on 

 trays or in baskets which are installed in the troughs and supplied 

 with a free circulation of water. 



The standard trough used at stations of the Bureau of Fisheries 

 is 14 feet long, 14 inches wide, and 8 inches deep inside. It is con- 

 structed of white pine, cedar, or cypress, from 1 to 2 inches thick 

 (usually If inches) and is coated inside with asphaltum. Hatching 

 troughs are usually arranged in pairs with aisles between, and, when 

 desirable, the water may be passed through two or more series of 

 troughs standing on different levels. 



Each hatching trough is usually divided by galvanized iron dams 

 into compartments large enough to accommodate the particular type 

 of egg tray or basket in use. The dams are arranged in such a man- 

 ner as to cause the water to flow over the dam at the head of the com- 

 partment, under the succeeding dam, then up through the trays or 

 basket of eggs, and so on throughout the length of the trough."^ By 

 placing the trays or baskets alternately, the first against the upper 

 dam, the succeeding one close to the lower, and so on, all of the water 

 is forced up through the eggs and utilized instead of passing around 

 them. 



