Hard water maybe undesirable because it generally 

 contains obnoxious gases such as carbon dioxide, nitro- 

 gen, hydrogen sulfide, and marsh gas. All of these 

 are injurious to fish by actually poisoning or as- 

 phyxiating them. Other waters may contain excessive 

 quantities of iron. In nearly all of these instances, 

 the water can be purified and made suitable for fish 

 by running it over a series of falls or baffles and by 

 storage in a reservoir with a large surface area to 

 permit thorough aeration. Spring and artesian water 

 should be tested beforehand by placing fish in it. A 

 temporary pond or trough may be employed for the purpose. 

 If possible, the fish should be held in the pond or 

 trough for a whole season in order to obtain a good 

 test; however, a shorter period, perhaps a month, may 

 be sufficient. If the fish remain alive, the water can 

 be considered suitable. 



Permanent construction should include a reservoir 

 at the spring itself. This reservoir may be of concrete 

 or riprapped with stone or brick for protection. A way 

 must be provided so that excess water from the supply 

 can be diverted around the pond or ponds. A sufficient 

 flow should be provided to compensate for seepage and 

 evaporation from the ponds during the propagation season. 



Natural water supplies, such as creeks, lakes, 

 rivers, or ponds, may be utilized as a source of water 

 but should be considered only when springs or artesian 

 supplies are not available, or where the natural sources 

 have all the necessary attributes of a good water sup- 

 ply. These sources are subject to change in volume, 

 temperature, and turbidity and may be polluted. In 

 addition, they generally contain undesirable species 

 of fish which may prey on minnows and reduce production 

 of the pond. No hatchery operator has successfully 

 screened undesirable fishes from ponds except by the 

 use of 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 excessive 

 silt may gradually fill the ponds to which the water 

 is supplied. Turbid water also reduces productivity 

 by restricting light penetration and, as a consequence, 

 the development of food organisms. Where the turbidity 

 is periodic and of short duration, the water can be 

 by-passed downstream. 



The volume of water must be kept within certain 

 limits throughout the year, this volume to depend upon 



