The source of inflow water greatly influences water quality. 

 Surface waters may contain wild fish, pathogens, and toxic 

 pollutants from agricultural run-off and industrial discharges. 

 Well water is usually low in oxygen and may contain undesirable 

 levels of nitrogen, ammonia, carbon dioxide, sulfur, sulfides, or 

 dissolved metals. However, it appears that maintaining an adequate 

 level of dissolved oxygen is usually the major water quality 

 problem in ponds. 



Ponds require vastly different approaches to maintain water quality 

 and successfully manage the resultant effluents, depending upon 

 their size and the kind of aquatic animal being raised in them. In 

 smaller ponds, water quality may be quickly improved by draining 

 and re-filling with fresh water. In larger ponds it is sometimes 

 necessary to use various aeration devices. These devices agitate 

 the surface, spray water into the air, or otherwise increase the 

 transfer of oxygen from air to water. 



In some cases, pond effluents may be of higher quality than 

 receiving waters since the majority of waste materials are retained 

 on the pond bottom. Because of the relatively good quality of 

 effluent from ponds, usually little or no treatment is required 

 before discharge into receiving waters. 



Raceways and Intensive Culture Systems '' 



For many intensively cultured species, water quality, not physical 

 space, limits the number of animals that can be reared in a raceway 

 or similar system. Water must be continuously added to flush away 

 wastes and to maintain a quality environm.ent . 



Water usually flows through raceways by gravity. However, in some 

 raceways, effluents from downstream sections are pumped back 

 upstream and reused. The effluent may first be improved by 

 aeration, filtration, sedimentation, ozonation, or a combination of 

 these and other processes before recycling. In single pass 

 raceways, where water is used only once before being discharged, 

 incoming water quality depends on the source. 



Effluent quality from intensive systems is a function of the number 

 and size of fish or other organisms, the feeding rate, and water 

 flow rate. 



Cages and Pens 



Aquatic organisms may be confined at very high densities in cages 

 or pens placed in ponds, lakes, rivers, and estuaries. Mollusc 

 cages may be suspended from piers, long lines, or rafts. Water 

 quality within cages and pens depends primarily upon both the 

 quality of water in the surrounding area and the rate of exchange 

 by circulation through these aquaculture units. Cages and other 

 devices placed in estuarine areas with tidal flows are flushed by 



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