Assessing the potential of an aquaculture operation is a complex process. It requires the systematic evaluation of marketing potential, capital risk, and personal commitment to the project. Only after this is done should a potential production site be considered.
This publication can help in assessing a site’s potential for the construction of levee ponds, which includes evaluating physical resources and legal and regulatory issues.
Unless any potential problems identified in the process can be mitigated or avoided through cost-effective methods, the site should be rejected.
The primary sources of information needed to conduct the site evaluation are various government agencies or private businesses (Table 1). Contact these groups early in the process.
A good place to start is with the Extension Aquaculture/Fisheries Specialist at the land grant university in your state.
Consulting services for site selection, pond construction, and water drilling are also excellent sources of assistance.
Water sources:
One of the first things to do in selecting a site for aquaculture ponds is to make sure that you have an adequate supply of suitable quality water. The amount of water required depends on the species to be cultured, the culture method, the soil type, climatic conditions (particularly precipitation and evaporation), and the size of the operation.
Groundwater is the preferred water source for levee ponds. It provides a dependable supply of water with a stable temperature and is less likely than surface water to be contaminated with wild fish, waste products, or pesticides.
The well depth, potential yield, and the geology of the water-bearing formation determine well construction and pumping costs, so shallow aquifers less than 250 feet (76 m) deep are preferred. Talk with local water-well drilling companies, state water resource agencies, or local fish producers to assess water availability and water quality.
If insuffcient information is available, it may be necessary to drill a test well. Personnel in the county office of the USDA Natural Resources Conservation Service (NRCS) or water management district office should be able to supply information about permit procedures.
The water from free-flowing springs can be a suitable groundwater supply if it can be captured at or very near the source. It is important to determine the spring’s flow rate to adequately assess the size of operation it can supply.
After the pond is filled, subsequent flow should be diverted so that solar radiation can increase water temperature and so that fertilizers, phytoplankton, or natural food sources will not be diluted. The diversion system (open ditch or pipe) will require an adequate amount of space and should be considered when evaluating the site.
Before you decide to use spring waters, assess the potential impact on downstream environments and the legal rights of downstream water users. Surface water sources include streams, rivers, lakes and reservoirs. Surface waters are less desirable than groundwater because they may not provide a constant supply all year and may contain pollutants.
The water quality of surface waters can vary widely, especially during droughts or floods. Wild fish in surface waters can contaminate cultured stocks, compete for food, and serve as vectors for infectious diseases.
If surface waters must be used, the water should be filtered or screened, though screens are not practical for debris-laden waters or where large quantities of water must be filtered. Large streams should not be diverted to supply aquaculture ponds because of the problems this could cause downstream.
Seek a regulatory opinion concerning the legal implications of diverting surface water sources. There must be suffcient water volume to fill ponds quickly and to replace losses from evaporation and seepage.
Ideally, a producer should be able to fill a pond within 14 days to prevent production delays and weed growth. A standard recommendation is to have a water source capable of delivering about 25 gallons/minute/acre (250 L/minute/hectare). Table 2 shows the time required to pump different volumes of water at different pumping rates.
The primary factors in assessing water quality will be the requirements of the cultured species. Once the absence of contaminants has been ensured, salinity is probably the most important consideration. Marine species have salinity requirements that may vary with the life stage cultured. Most pond aquaculture of marine species uses brackish water or seawater from surface sources, so all of the mineral requirements are met.
Most freshwater fish are raised in water with less than 0.5 ppt salinity, although some freshwater species grow well at salinities up to 7 to 8 ppt. For groundwater sources, most of the other important characteristics will change after the water is pumped to the surface and impounded.
Water temperatures will be influenced by ambient air temperature and solar radiation. When exposed to air, dissolved oxygen and carbon dioxide will approach equilibrium with the partial pressures of these gases in the atmosphere.
Dissolved ferrous iron will precipitate as ferric oxides after exposure to rising pH and dissolved oxygen. Hydrogen sulfide will be degassed or oxidized to harmless sulfate after exposure to oxygen. Total alkalinity and total hardness will reach equilibrium after exposure to mineral rich soils.
If a soil test reveals low mineral content, agricultural limestone may be added to the pond bottom before filling the pond. If surface waters are used, there will be little change in water quality after impoundment.
Surface waters that are consistently turbid will introduce suspended soil particles or other solids that, if not settled, could interfere with biological processes in the pond. Low pH water coming from acid-sulfate soils or active mining sites should not be used.
Author:
Jimmy L. Avery
