Site selection and design

Stuart J. Rowland, Biologist, Grafton Aquaculture Centre

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 a growout facility for the aquaculture of finfish; most factors also apply to crustaceans.

Selection of a region

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.

Characteristics of Extensive and Intensive Systems

Characteristics of Extensive and Intensive Systems

In extensive aquaculture systems, fish are stocked at relatively low densities in earthen ponds. Feeding is based partly or completely on the natural food in the ponds. Extensive cultures needs only enough water to fill and maintain the water level in ponds.

In intensive aquaculture, fish are stocked at high densities in troughs, raceways, tanks, cages or small ponds. Their growth is based mainly on artificial feed (normally specially formulated diets in pellet form). As the level of intensity increases (that is, as stocking density increases) the level of management and technological input also increases for successful culture.

Site selection

Water is the medium surrounding aquatic animals and their well being is dependent on the abundance and quality of the available water.

A regular, abundant water supply is essential for the maintenance of healthy fish stocks. This applies particularly for those species that need flowing water with high oxygen levels (for example the salmonids). A reasonably abundant supply is also required for native fishes, particularly during spring and summer when water temperatures can exceed 30^o C and poor water quality conditions can develop, necessitating a rapid exchange of water.

Under the severe climatic conditions in Australia, the supply of water must be guaranteed during drought periods, which can last three or four years in the inland regions. The quantity of water will determine the holding capacity and production potential of a facility.

A supply of good quality water is also essential. Poor water quality reduces fish survival and growth. The water supply must be relatively free of nutrients, sewage and other dissolved wastes, heavy metals, oils, pesticides, herbicides, chlorine, methane, hydrogen sulphide and other poisonous substances. Do not use water of extremely high turbidity (caused by silt and clay colloids) as it may stress fish, reducing growth and resistance to disease.

Water quality variables need to be monitored regularly as they interact and can change from acceptable levels to lethal levels within several days, particularly during summer. Monitor temperature, dissolved oxygen, pH and ammonia.

Source water for fish farms can be drawn from many sources; for example runoff, rivers, creeks, impoundments, small dams, lakes, irrigation canals and underground (bore water). The type, size, location and topography of a farm will determine the best or most practical source of water. Bore water has a number of features that make it very suitable, particularly in intensive facilities.

Bore water profile:

• regular, dependable supply
• free of pathogens
• free of organic, agricultural or industrial pollution
• free of suspended particles and so allows close observation
• relatively constant temperature
• free of trash fish and other undesirable aquatic organisms.

Some sources of bore water are deficient in oxygen and contain excess nitrogen and harmful gases such as methane and hydrogen sulfide, and minerals such as lead, zinc and iron. These limitations can generally be overcome by storing and aerating the water in a reservoir before use.

Avoid water from domestic supplies as it contains chemicals such as chlorine, which can be toxic to fish.

The cost of supplying water to the site may be a major factor determining the economic feasibility of a fish farm. Pumping costs are high and must therefore be minimised. Utilise gravity flow, as it is efficient and cheap. Use a large reservoir to implement gravity flow.

Soil

Pond floors should contain impervious soil to eliminate or reduce the loss of water by seepage. Clay or clay-loam soils are ideal. Loamy soils can be well compacted using sheepsfoot rollers or bulldozers; the soils may leak slightly in the early stages but will seal.

Ponds constructed in sandy or other porous soils can be made watertight by lining the bottom and sides with clay. Bentonite seals ponds; however, it is costly. Survey the proposed site for gravel or sand layers, rock strata and other soil characteristics that may interfere with water holding qualities.

If the land was used for crops, test the soil for accumulated pesticide residues. Avoid areas with acidic soils.

Areas with high ground water cause problems. It is difficult, or impossible, to build ponds; if ponds are built they cannot be completely drained and dried, steps which are necessary for efficient management.

The area of land selected for a fish farm should be large enough to include the maximum number of ponds required plus a hatchery and laboratory complex, spawning facilities, holding tanks and sheds. Consider future expansion when selecting the land.

The land should be flat and slope gently away from the source of water or reservoir. An area for the accumulation of surplus water should be available below the ponds. An 'open' site is advantageous because it allows wind to aerate water in the ponds.

Topography will determine the type of ponds to be constructed (that is, excavation, levee or gully). A topographic survey will determine the feasibility of constructing a fish farm on a particular site and will ensure that the land is used efficiently.

Other factors

Other important factors that must be considered include;

• susceptibility of the site to flooding
• availability of electricity
• availability of suitable manpower to operate the farm
• availability of transport for the dispatch of fish
• proximity of markets
• ability to secure the site against poaching and sabotage
• potential impact on neighbors and environment.

In general, the selection of a site for a fish farm should be based on a thorough knowledge of local geography and local and regional hydrology, geology, climate and weather.

Design of earthen ponds

Earthen ponds comprise the major capital investment in aquaculture facilities throughout the world. More than 90 per cent of the total global production is from ponds. The ponds and buildings should be laid out for efficient and economic operation and the best utilization of the land. Construction of ponds and drainage systems should be planned and supervised by both an aquaculturist and an engineer, particularly if a large system is to be constructed.

Type and Shape

The topography of the land will in part determine the type and shape of some or all of the ponds.

There are three basic structural types of ponds. The most common type is the excavated pond in which earth is removed and used for building the banks. This type of pond can be constructed on flat or undulating land. Levee ponds are constructed on very flat land and are similar in structure to rice bays except that the banks must be high enough to contain the necessary depth of water.

Gully or ravine ponds are restricted to hilly country and are constructed by damming valleys or gullies.

Ponds should be square or rectangular to make the most efficient use of available land. It is more economical to construct square ponds; however, rectangular ponds are easier to manage.

Supply and drainage

Each pond should have a separate inlet and outlet. Both should be screened; the inlet to prevent the entry of trash fish and other undesirable aquatic fauna, and the outlet to prevent the loss of stocked fish.

The diameter of supply and drainage pipes should be at least 15 cm. Lay all pipes underground and do not plant trees close to drainage or supply lines.

Construct ponds so that they can be drained individually, completely and rapidly. This will enable the removal of all fish during harvesting and facilitate efficient management, particularly when water quality and disease problems occur. Complete drainage can be achieved by a raceway or well in the deeper section of the pond. The bottom of the pond should be level and slope gradually towards this area.

The outlet structure should enable the adjustment of water level and also allow for the overflow of excess water. It is important that water can be drained from the bottom as well as the surface, so that the 'dead' water (low or deficient in oxygen) can be removed.

Each pond should have a deep (at least 2 metres) and a shallow (1-metre) section; however, the preferred depth varies with the species and the locality. A deep section has the following advantages:

• the deeper water is a buffer against extreme temperatures in summer and winter
• facilitates harvesting
• increases production (at least up to depths of about 3 metres)
• reduces evaporation during summer
• reduces or eliminates the growth of macrophytes

Construct banks wide enough to ensure strength, stability and vehicular access. The latter is extremely important and enables efficient management of ponds. Build banks with slopes of about 3: 1. Line the banks with topsoil and plant with grasses to ensure stability and prevent erosion. Use animals to eliminate or reduce the need to mow pond banks. Cattle should not be used as they erode the banks and may enter the water and increase turbidity and nutrients to undesirable levels: sheep or goats are a better alternative.

There is a large variation in the size of earthen ponds used in aquaculture throughout the world and authorities disagree on the optimum size of ponds. Ponds used in the channel catfish industry in the United States of America vary from less than/0.4 hectares to 40 hectares; ponds in Israel are generally no larger than 10 hectares. Ponds range from 0.1 to 1.0 hectare in the silver perch industry.

A number of factors will determine the preferred size of ponds on each farm: the function (that is, broodfish, larval rearing, grow-out) fish species to be farmed, techniques and stocking densities, cost of land, topography, capital and equipment available for construction and the planned production capacity.

Large ponds have a lower cost of construction per unit area than small ponds, however there are a number of disadvantages in using large ponds:

• difficult to monitor and control disease outbreaks
• difficult to manage water quality problems
• difficult to control algae blooms
• costly to control disease outbreaks and algae blooms, as the entire pond must be treated
• erosion of banks
• difficult to sample or catch fish
• slow to drain, leading to stress, deterioration of water quality and possibly predation by birds during and after harvest, there is a large quantity of product to handle and market.

Construct ponds no larger than about 2ha to enable the efficient management necessary under intensive conditions.

Advantages/Disadvantages of Extensive and Intensive Systems

Buildings and equipment

The following buildings, rooms and equipment are essential components of an aquaculture facility and their design and location should be planned so that space, labour and equipment are used efficiently and economically. These are:

• office
• toilet and washroom
• laboratory
• meal room
• general workroom with tanks for holding, sorting, quarantining and treating fish, with vehicular access
• plant room with filters and airblowers
• store rooms for chemicals, feed, equipment
• garages for vehicles, boats, pumps, traps, nets, mowers
• workshop for repairing and making equipment
• handling and packaging room for preparing fish for packaging and dispatch

Further Reading

Brown, E.E. & Gratzelc, J.B. 1980, Fish Farming Handbook, Food, Bait, Tropicals and Goldfish, AVI, Conneticut.

Huguenin, J.E. & Colt, J. 1989, Design and Operating Guide for Aquaculture Seawater Systems, Elsevier, Amsterdam.

Merrick, J.R. & Lambert, C.N. 1991, The Yabby, Marron and Red Claw Production and Marketing, JR Merrick, Artarmon.

Piper, R.G., McEIwain, I.B., Orme, L E., McCraren, J.P., Fowler, L G. & Leonard, J.R., 1982, Fish Hatchery Management, US Department of the Interior, Washington.

Reynolds, L.F. (Editor) 1986, Proceedings of the First Freshwater Aquaculture Workshop, Narrandera, February 1983, NSW Agriculture & Fisheries, Sydney.

Rowland, S J and Bryant, C 1995. Silver Perch culture. Austasia Aquaculture for NSW Fisheries.

Shepherd, C.J. & Bromage, N.R. (Editors) 1988, Intensive Fish Farming, BSP Professional Books, Melbourne.

Spotte, S. 1979, Fish and Invertebrate Culture, Water Management in Closed Systems, Wiley, Brisbane.

Tucker, C.S. (Editor) 1986, Channel Catfish Culture, Elsevier, Amsterdam.

Wheaton, F.W. 1977, Aquacultural Engineering, Wiley, Brisbane.