Monday, November 10, 2008

Site Selection for Aquaculture

Introduction


The success of an aquaculture enterprise is dependent on many factors including the selection of a suitable site and the design and construction of facilities that enable efficient and economic operation. This information briefly discusses the major factors that must be considered when selecting a site and designing grow out facility for the aquaculture of finfish; most factors also apply to crustaceans. Success or failure of any aquaculture venture largely depends on the right selection of the site for it. In choosing a site several factors other than the physical aspect of the site are to be considered.


Sites suited for aquaculture and culture types


Several types of water bodies can be used for fish culture - the choice of a specific body would depend on the objective of the investors and also the type of aquaculture.


Among the sites suitable for aquaculture could be listed: land-swamps, rivers, stream beds; coastal areas - bays, estuaries backwaters, lagoons, salt marshes and mangrove swamps; lakes, reservoirs and other water bodies, including irrigation tanks and canals.


The specific site to be chosen would be based on the requirement of the culture systems. Static water ponds are the most common, hence pond culture the most important system. Most of these are confined to freshwater areas, but brackish water ponds are also becoming more common. There is a variety of culture systems which can be developed in open waters - the stocking and management of open waters themselves being major occupation, e.g. extensive stocking of man-made reservoirs and lakes. In the larger freshwater bodies and coastal areas cage and pen culture can be developed. Site selection for these culture systems has to be carefully done, based on the requirements of the species to be cultured and the structures to be erected for the culture. Here and in the culture systems where closed systems are used, the inputs required can be costly and management intensive. Thus there can be gradation of culture, systems based on the input costs and management strategy employed, from extensive, through semi-intensive to intensive.


Culture types (Systems)


The different culture systems in vogue are listed below:


Static water ponds, running water culture, culture in recirculation systems (closed or reconditioned water); culture in rice fields and integrated culture systems, as the duck-cum-fish and pig-cum-fish culture - or any fish-livestock-crop combination; culture in raceways, cages, pens and enclosures; also mollusk/oyster culture - hanging, on-bottom and stick methods. As mentioned already the choice of site for a specific culture system, would depend on the characteristics of the site and the requirement of the culture system - the latter again has two components, the species requirements and the structural requirements of the culture system.


Various Factor Affecting the Site Selection of Aquaculture:


1. Socioeconomic and Political factor:
They are socio-economic aspects such as
Social and religious customs’
Consumer preference;
Nature of manpower (labor) - quality and quantity - available;
Transportation and communication facilities; i.e. infrastructure facilities;
Accessibility and nearness to market;
Availability of construction materials

2. Political and Legal Consideration:

The aquaculture project execution should be a part of the overall planning for the specific area under the national plan for development, so that the project can fit into the country's or provincial plan for development of industry and agriculture. This is specially needed when aquaculture is a part of rural development programme, as indeed most such projects are. This should specially help in sharing infrastructural facilities of transportation (road), power supply and communications and also in judicious sharing of imports and recycling outputs. The advantages of their consideration in sitting a project are obvious. We shall look into these aspects of macro-economic planning subsequently when “socio-economic aspects” and “aquaculture planning” are discussed in detail. Legal aspects, such as security of tenure, maritime laws controlling coastal waters (in cases where sites are coastal), legal size limits with reference to the ponds/culture area, as well as the species under culture, and closed reasons, should also to be considered. Several countries already have certain regulations concerning these legal aspects, some of which are in force, much before aquaculture was thought of as an industry.
In many cases these legal clauses cannot be easily modified, even though some attempt in this direction would be necessary, especially with reference to size-limits of fish and closed seasons. The latter regulations have been included to protect the species' survival under intensive capture systems of wild stock. While this protection may be necessary for such a case, here in aquaculture, and capture from the wild fish of certain size, when the season for capture is closed legally, is only for protection of the fish by way of transferring the fish to culture ponds - either as brood fish or as fry or fingerlings in grow-out ponds. In some cases maritime areas through which navigational routes and certain other country priorities exist. These aspects should be considered in choosing the site for the aquaculture ventures planned.
3. Major Climatic and Environmental factor:

Climatic factor: Fishes and crustaceans are poikilotherms (cold-blooded animals) and temperature directly affects all aspects of their biology. Each species has a range of temperatures in which it can live. Temperatures reaching the upper or lower lethal limits will kill the animals. If animals are subjected to extreme but not lethal temperatures for extended periods, growth and other biological activities will be adversely affected and mortalities will occur; either directly through malfunction of one or more physiological processes or indirectly (for example, through stress-induced disease and starvation). Within the tolerance range, each species has a range of temperatures, which enable maximum growth (the optimum temperature range). At temperatures outside this range, feeding rates and the efficiency of food conversion are generally poorer, resulting in slower growth and lower production. Locate aquaculture facilities in an area that has the optimum temperature regime for the selected species. Regions where lethal temperatures are reached, or approached, are unsuitable for pond culture.

Other Environmental Factors:

a) Topography and Ground Elevation: Large commercial fish farms are typically built on flat land. Pond bottoms drop approximately 0.2 foot for every 100 feet of length, a slope of 0.2%. Topography with slopes of 0-2% is better for pond construction. Extensive earth moving may be required on land with slopes greater than these; increasing construction costs. Some innovative farmers use terracing -- stair-stepping -- for pond layouts in hollows or on land with slopes greater than 2%. However, the economics of that method should be carefully examined. It is important that ponds have an adequate drainage area for harvest. The site should be above the 25-year flood plain.
b) Soil: the site must have soils that hold water and can be compacted. If pond levees are constructed with soil that has high water permeability (leakage), the cost of pumping water could become prohibitive. Soils should contain no less than 20% clay. Soils with high sand and silt compositions may erode easily and present a piping hazard -- soil-water flow along pipes -- which could wash out a levee. Anti-seep collars can help minimize that problem. Clay oil with greater than 40% clay is suitable for pond and pond dyke construction. Silt clay (40-60% clay), sandy clay (35-55% clay), Clay loam (27-40% clay) are also suitable for aquaculture site.
c) Water Supply, Water Quality: Aquaculture requires large volumes of good quality water. While you may be able to fill a pond with your garden hose, it may take six months to do so. Normally, a well or surface water source (river, stream or spring) is required. Surface sources may be polluted, intermittently available (affected by weather, e.g. drought) or contain wild fish populations which might be introduced into your pond. Wild fish can be a source of disease and will often compete with cultured fish for feed. Many of the most successful aquaculture operations in the U.S. depend on large aquifers (underground water supplies) for water needs. Typically, commercial aquaculture requires a water flow rate of 25-40 gallons/minute, on demand, for every surface acre (4 acre-feet) of pond water. Water must be of high quality and free of pollutants, sewage and toxic contaminants. Generally, water that is safe for livestock and domestic use or that supports wild fish populations is safe for aquaculture. However, livestock and aquaculture do not mix. Manure from just a few farm animals can pollute a pond. There are several chemical characteristics of water that are desirable for good fish growth. Water should have a pH of 6.5-9.0, total alkalinity of 75-250 mg/l and total hardness of 75-250 mg/l. Total hardness and alkalinity should not be less than 20 mg/l. Low alkalinity and acid water are usually related to acid soils. Agricultural limestone can be used to raise pH, alkalinity and hardness to the minimum required levels in soft, acid water. If striped bass or red drums are being considered, calcium hardness and total alkalinity between 100-250 mg/l are preferable; a calcium hardness value of 250 mg/l is ideal. Often, well water contains no oxygen and high levels of carbon dioxide and nitrogen, necessitating aeration before use or pH testing.
d) Productivity: The soil must be productive and fertile enough to produce require micro and macro vegetation of the pond and planktonic growth.
e) Other Factors:
· Susceptibility of the site to flooding
· Non availability of migratory birds, predators
· Previous land use and surrounding land use
· Environmental Consideration: Aquaculture is an Environmentally Relevant Activity and will require an Environmental Authority or approval from the Environmental Protection Agency (EPA) to authorize activities
· Wind drift and Arial application

No comments: