I028 BULLETIN OF THE BUREAU OF FISHERIES. 



the fish when the water is drawn out of the rest of the pond for cleaning. 

 The cleaning process itself is simphfied, since a man may enter for the pur- 

 pose and walk about on the bottom of the pond. 



So far the pond is not provided with any outlet. In the wall opposite the 

 intake, 0.15 or 0.20 meter above the gutter in the bottom of the pond, is an 

 aperture 0.50 to 0.60 meter square, covered with wire netting. This, however, is 

 not an outlet but an overflow. The outlet proper is in the bottom of the large 

 circular basin and consists first of an opening 0.60 meter square and o. 10 too. 12 

 meter deep. Into this square is set a wooden box with a wire mesh bottom, 

 and this box, filled with coarse gravel, rests upon an iron grating 0.60 by 0.60 

 meter. Below the grating is a circular basin 0.50 meter in diameter and o.i 5 

 meter in depth, with an opening in the center which leads into an outflow pipe. 



The outlet provided, the regulation of the water level in the pond remains 

 to be accomplished. This is done by carrying the outflow into a tank or other 

 receptacle outside the pond, in which any desired level may be maintained by 

 regulation of its overflow. The latter is controlled by a board wall or dam con- 

 structed of removable sections. 



In addition to the convenience of this construction in regulating the height 

 of water in the ponds, there is afforded every protection against loss of the small 

 fish, since the water in leaving must pass through gravel the size of hazel nuts; 

 the cleaning of the pond may be accomplished without injury or shock to the 

 fish; all impurities fall into the gutter and are carried off through the circular 

 basin, while the fish, seeking the incoming current, are in the upper strata of 

 water and away from all such impurities as do not pass through the screened 

 outlet; the fish are provided with desirable currents derived from the action of 

 the siphon, and the pond is continuously self-cleaning. When the fish are 

 larger the gravel may be removed, and still later the screen itself may be 

 discarded. 



Fish culturists will appreciate the importance of perfect control of their 

 rearing ponds. A construction such as this described is possible wherever there 

 is a fall of at least_ i meter in the water supply, since it is not necessary to take 

 the siphon apparatus into account. There is but one thing absolutely necessary 

 to provide against — namely, the possibility of emptying the pond entirely, 

 down to the screen with the gravel. It is of little importance that the outflow 

 pipe is not emptied ; the water will always flow off, on account of the difference 

 of level. 



The design has been adopted with satisfactory results in several fish culture 

 establishments in France. 



