222 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



minute. The difference of level between the source and mouth of the brook is about 

 190 feet. The sharpest descent is just above the hatchery and rearing troughs, which • 

 therefore receive well-aerated water. The conformation of the ground offers good 

 facilities for the distribution and utilization of the water. 



The leading motive in the foundation of this station was the desire to apply to the 

 Atlantic salmon the system of rearing fish to the age of at least several months before 

 liberating them. This motive has determined not only the principal subjects of the 

 work, but also to a considerable extent the fixtures and methods. The scheme of 

 work was determined in outline several years before the acquisition of full title to the 

 premises, and, circumstances rendering it desirable to enter at once on its develop- 

 ment, it became necessary to have recourse to movable apparatus, pending authority 

 for permanent improvements. Hence the erection of a series of small troughs in the 

 open air, which gave such excellent satisfaction that enlargement took the same direc- 

 tion; and it has thus come about that the rearing operations of the station down to 

 the present time have been almost exclusively conducted in open-air troughs. A 

 series of ponds has been constructed, but with the exception of a few small ones none 

 of them have been as yet brought into use. 



The troughs are for the most part such as are used in the hatchery for the 

 aiaturing o'f spawn, and their form and size have been adapted to the hatching appa- 

 ratus which has been in use at the Maine station for many years. The eggs are 

 developed on wire-cloth trays measuring 12.} inches in width and length, and the 

 troughs are therefore 12f inches wide. Their depth is 9 inches and their length is 10 

 feet inches. Such short troughs were adopted for two reasons: (1) It was though! 

 that a greater length might involve the exposure of the eggs near the lower end to 

 the danger of a partial exhaustion of the air from the water by the eggs above them; 

 (2) these short troughs are very convenient to cleanse and to move about for repairs 

 or other purposes. They are made of pine boards seven-eighths inch thick. On the 

 inside they are planed and varnished with asphaltum. When used for rearing lisk 

 each trough is fitted with a pair of thin wooden covers reaching its entire length, 

 hinged to the sides and meeting each other, when closed, at a right angle, forming, 

 as it were, a roof over the trough. When closed they protect from predatory birds and 

 other vermin ; when open they are fixed in an upright position, in effect adding to the 

 height of the sides and preventing the fish jumping out. The time spent in opening 

 and closing the troughs is by this arrangement reduced to a minimum. 



Water is fed through wooden tubes, and the volume admitted is regulated by slides. 

 The exit of the water is through another tube or hollow plug standing upright near 

 the lower end of the trough, and by its height governing the depth of the water. The 

 outlet tube is movable and is taken out in cleaning. A wire-cloth screen just above 

 the outlet tube prevents the fish escaping. 



In a trough of standard size 2,000 fry are generally placed, and to accommodate 

 the large numbers of fish reared we bring into use sometimes nearly 1M)0 troughs, 

 which are of necessity placed in the open air. They are arranged in pairs with their 

 heads against the feed troughs, supported by wooden horses at a convenient height 

 from the ground. They are given an inclination of about 2 inches to facilitate cleaning. 



The volume of water fed to each trough has varied from time to time, but is ordi- 

 narily about 5 gallons per minute, which renews the water every four minutes. The 

 ordinary arrangement is to use the water but once in the troughs, letting it waste 



