Water supply The most common sources of water used for aquaculture are surface waters (streams, springs, lakes) and groundwater (wells, aquifers). Of these, wells and springs are generally preferred for their consistently high water quality. • The quantity and quality of water should be adequate to support production through seasonal fluctuations. • Determine that the quality of the intended water source is good enough for fish to thrive in. wwA good water source will be relatively free of silt, aquatic insects, other potential predators, and toxic substances, and it will have a high concentration of dissolved oxygen. wwIf fish are already living and reproducing in the water (for example a river or lake), this is usually an indication that the quality is good. wwFind out if the quality remains constant throughout the year or if there are seasonal changes that result in poor quality at certain times. • Make the final site selection based on both the quality and quantity of water available. • The quantity of water required depends on the species to be cultured and on the anticipated management practices, for example whether ponds will be operated as static ponds (no water flowing through) or as flow-through systems. Figure 1.1-2. A good water source is one that provides high quality water in sufficient quantity throughout the year. Supplying water to ponds by gravity is preferable. Water supply The most common sources of water used for aquaculture are surface waters (streams, springs, lakes) and groundwater (wells, aquifers). Of these, wells and springs are generally preferred for their consistently high water quality. • The quantity and quality of water should be adequate to support production through seasonal fluctuations. • Determine that the quality of the intended water source is good enough for fish to thrive in. wwA good water source will be relatively free of silt, aquatic insects, other potential predators, and toxic substances, and it will have a high concentration of dissolved oxygen. wwIf fish are already living and reproducing in the water (for example a river or lake), this is usually an indication that the quality is good. wwFind out if the quality remains constant throughout the year or if there are seasonal changes that result in poor quality at certain times. • Make the final site selection based on both the quality and quantity of water available. • The quantity of water required depends on the species to be cultured and on the anticipated management practices, for example whether ponds will be operated as static ponds (no water flowing through) or as flow-through systems. 4 wwColdwater species like trout require a lot of water because they prefer a continuous supply of clean water with high dissolved oxygen concentrations (above 9 mg/L). wwWarmwater species like tilapia can tolerate water with lower dissolved oxygen levels, so tilapia culture is often done in static water, that is, without water flowing through the ponds. However, the best situation is to have a lot of “free” water, meaning water available by gravity flow, even if it is not always being used. • For earthen ponds, the water source should be able to provide at least 1 m3 of water (1000 litres) per minute for each hectare of ponds that will be built. This quantity will be sufficient for quickly filling the ponds as well as for maintaining water levels throughout the culture period. • If the selected site has relatively poor soils (i.e., soils containing too much sand) the source should be able to provide two to three times more water (2-3 m3 per minute per hectare). This quantity of water will be sufficient for maintaining water levels to compensate for losses that are likely to occur through seepage. Soil • Land should be comprised of good quality soil, with little or no gravel or rocks either on the surface or mixed in. Areas with rocky, gravelly, or sandy soil are not suitable for pond construction. • The soil should be deep, extending down at least 1 metre below the surface. There should not be layers of rock lying close to the surface. • Soils in the area where ponds will be built should have clay layers somewhere below the surface to prevent downward seepage. • Soil that will be used to build the dykes must contain at least 20% clay so the finished pond will hold water throughout the growing period. • Some soil with a higher clay content—preferably between 30 and 40%—should be available nearby. It will be used to pack the core trenches in the dykes. Other factors to consider 1. Proximity to a market • Does market demand justify production? • Will the existing physical infrastructure meet the farmer’s needs for marketing the fish? • Will there be sufficient demand nearby or will transporting to a distant market often be a necessity? It is easier to sell at your doorstep or to have a permanent buyer who takes everything you can produce and either picks the fish up or is close enough that you can deliver the fish to them.
