ESTABLISHING THE HATCHERY 



ery operator has successfully 

 screened undesirable fishes from 

 ponds, except by using expensive 

 and elaborate gravel filters. 



In selecting a stream to provide 

 water for rearing ponds, one should 

 take into consideration, primarily, 

 the fluctuations in volume and- the 

 amount of turbidity. Turbidity is 

 particularly important because ex- 

 cessive silt may gradually fill the 

 ponds to which the water is sup- 

 plied. Turbid water also reduces 

 productivity by restricting light 

 penetration and, as a consequence, 

 the development of food organisms. 

 Where turbidity is periodic and of 

 short duration, the water should be 

 bypassed downstream. 



The volume of water must be kept 

 within certain limits throughout 

 the year, depending on the num- 

 ber of ponds operated. Fortu- 

 nately, by building proper struc- 

 tures, a suitable volume of water can 

 be obtained. If the stream flow is 

 constant or if the fluctuation in vol- 

 ume is within narrow limits, suf- 

 ficient water may be obtained by the 

 building of a low dam (fig. 2). 



This dam should be located so 

 that water can be obtained for the 

 ponds by gravity flow. The water 



control structure should be of con- 

 crete and equipped at one side with 

 an intake box from which the de- 

 sired amount of water may be ob- 

 tained for the pond system. Dams 

 of low head provide no obstacle to 

 flood wa.ters and allow debris to 

 pass over readily without obstruct- 

 ing flow. Where the flow is inter- 

 mittent or becomes considerably 

 reduced during the dry season, it 

 may be necessary to make a larger 

 impoundment by constructing a 

 higher dam. 



The dam should be anchored in 

 both banks of the stream with 

 bulkheads as high as the banks — 

 to protect the banks. The spill- 

 way should be built somewhat lower 

 than the bulkheads. A concrete 

 apron should be provided to keep 

 the water flowing over the spillway 

 from undercutting the dam. The 

 intake box should be provided with 

 a coarse grating to obstruct large 

 masses of debris. It should have a 

 slot in which a fine screen is in- 

 serted to keep out leaves and mate- 

 rials that might obstruct the flow 

 of water through the pipe to the 

 pond and to keep out other fishes. 

 So that the screen may be kept clear 

 of debris without too much diffi- 



FiGURE 2. — A low dam with outlet for supplying water to ponds. 



