56 



REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



The troughs are supported by a suitable framework at a conveuient 

 height from the ground aud arranged in pairs with their heads against 

 a long feed-trough, constructed of pine boards and perforated on the 

 side by the feed-pipes, over each of which is a capacious screen to pre- 

 vent clogging by leaves or other floating debris. A frame 6 by 12 

 inches, covered on its outer side by wire-cloth of ^ inch square mesh, 

 answers the purpose of a screen so well that water from an ordinary 

 brook can be admitted to the feed-trough without previous filtering or 

 screening aud with little or no danger of a stoppage of water in any 

 of the fish-troughs. Such screens over the feed-pipes might be made 

 the sole dei^endeuce, were it not that the labor attending their cleaning 

 would be greater than that required by a separate filter or screen. 



CoTbduzt to Unver level. 



Fish trough. 



Scale offeefc. 



Staud of Troughs for Rearing Atlantic Salmon. 



The system represented here by 12 troughs in two series may be 

 extended to many hundreds of troughs in four (or more) series, each 

 series on a different level and receiving water from the series next 

 above, the fall from one to another being about 4 feet. In the drawing 

 the series of 6 troughs on the left is supplied with water directly from 

 the upper "feed-trough" (i. e., supply- trough), and they discharge into 

 a catch-trough, from which the water is carried to the supply-trough 

 ("feed-trough") of the lower level. If the aqueduct supplies more 

 water than the upper series of troughs can use, the surplus x)asses by 

 way of the "overflow" directly to the catch-trongh and thence to the 

 supply-trough of the second series. With a fall of 4 feet, the catch- 

 trough and the conduits that lead from it are below the walks which 

 give access to the troughs on both sides and at the lower end. 



The number of fish assigned to a single trough is ordinarily 2,000, 

 aud the volume of water given them is commonly 5 gallons per minute. 

 Generally the water is used but once in troughs and is discharged 



