Water Sources And Quality

Sources of water for aquaculture include municipal supplies, wells, springs, streams, lakes, reservoirs, estuaries, and the ocean. The water may be used directly from the source or it may be treated in some fashion prior to use.

Most municipal water sources are chlorinated and contain sufficiently high levels of chlorine so as to be toxic to aquatic life. Chlorine can be removed by passing the water through activated charcoal filters or through the use of sodium thiosulfate metered into the incoming water at the proper rate. Municipal water is usually not used in aquaculture operations that require large quantities of water, either continuously or periodically, because of the initial high cost for the water and the cost of pretreatment to remove chlorine.

Most aquaculturists, if asked, would probably indicate a preference for well water over other sources. Both freshwater and saline wells are common sources of water for aquaculture. The most commonly used pretreatments for well water include temperature alteration (either heating or cooling); aeration to add oxygen or to drive off or oxidize such substances as carbon dioxide, hydrogen sulfide, and iron; and modification of salinity (in mariculture systems). Pretreatment may also include adjusting hardness and alkalinity through the application of appropriate chemicals. For example, limestone (CaC03) is commonly used to increase both hardness and alkalinity.

To heat or cool water requires large amounts of energy. A major consideration in locating an aquaculture facility is to have not only a sufficient supply of water but also water at or near the optimum temperature for growing the species that has been selected. The vast supply of spring water of almost perfect temperature in the Hagerman Valley of Idaho supports the majority of the rainbow trout production in the United States. Where geothermal water is available, tropical species can be grown in locations where ambient winter temperatures would otherwise not allow them to survive. Tilapia farmers have been successful in parts of Idaho and other states where geothermal water of suitable quality is available. Not all geothermal wells produce water of suitable quality, however. High levels of sulfur and other toxic chemicals are commonly found in geothermal water, so thorough testing should precede any attempt to use such water sources for aquaculture.

Another large cost associated with incoming water is associated with its movement. Many aquaculture facilities that utilize surface waters and those that obtain their water from wells other than artesian wells are required to pump the water into their facilities. Pumping costs can be a major expense, particularly when the facility requires continuous inflow or high volumes of makeup water to replace evaporative losses from ponds.

Surface water can sometimes be obtained through gravity flow by locating aquaculture facilities at elevations below those of adjacent springs, streams, lakes, or reservoirs. Coastal facilities may be able to obtain water through tidal flow.

The most common treatment of incoming surface water is removal of particulate matter. This can be effected through the use of settling basins or mechanical filters. Particle removal may involve the reduction or elimination of suspended inorganic material such as clay, silt, and sand. It may also involve removal of organic material, including living organisms. Organisms that will enter aquaculture facilities if not filtered from the incoming water include phytoplankton and zooplankton, plants and plant parts, macroinvertebrates, and fish. Some of the organisms, if not removed, can be expected to survive and grow to become predators on, or competitors with, the target aquaculture species. Very small organisms, such as bacteria, can be removed mechanically though filtering particles of a few microns in size; such removal becomes inordinately expensive if there are large volumes involved. In most cases, filtration of incoming water involves passing the water through screens of various sizes, the smallest of which is often no smaller than a window screen. If a situation calls for elimination of microorganisms, other forms of water treatment, such as ozonation and the use of uv radiation, are more efficient and effective than filtration.

For many freshwater species that can be characterized as warmwater (such as channel catfish and tilapia with an optimum of about 30°C) or coldwater (such as trout with an optimum of about 20°C), the conditions outlined in Table 4 should provide an acceptable environment. So-called midrange species are those with an optimum temperature for growth of about 25°C (examples are walleye, northern pike, muskellunge, and yellow perch). Typically, midrange species do well under the conditions, other than temperature, specified in Table 4 for coldwater species. Some species have higher or lower tolerances than others. For example, tilapia can tolerate temperatures in excess of 34°C but have poor tolerance for low temperature. Most tilapia species die when the temperature falls below about 12°C. Tilapia have a remarkably high tolerance for ammonia compared with such species as trout and salmon, which have a high tolerance for cold water but cannot tolerate water temperatures much above 20°C. Marine fish may be able to tolerate a wide range of salinity (such euryhaline species include many species of flounder, red drum, salmon, and some species of shrimp), or they may have a narrow tolerance range (they are called stenohaline species, examples of which are dolphin, halibut, and lobsters). Recommended water quality conditions for marine fish production systems are presented in Table 5.

The water quality criteria for each species should be determined from the literature or through experimenta-

Table 4. General Water Quality Requirements for Trout and Warmwater Aquatic Animals in Fresh Water

Table 5. Suggested Water Quality Conditions for Marine Fish Production Facilities

Variable

Acceptable level or range

Acceptable level or range

Table 4. General Water Quality Requirements for Trout and Warmwater Aquatic Animals in Fresh Water

Acceptable level or range

Variable

Coldwater

Warmwater

Temperature, °C

<20

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