Cover Image
close this bookAquaculture - Initial Environmental Assessment Series No. 5 (NORAD, 1992)
close this folderPart I: General account
View the document1 Characteristics of aquaculture projects
View the document2 The environment affected by the project
Open this folder and view contents3 Possible environ mental impacts
View the document4 Relevant literature

1 Characteristics of aquaculture projects

Aquaculture entails controlled farming or cultivation of organisms in salt, brackish or fresh water for the purpose of food production. Aquaculture produce is also put to good use in other connections, e.g. pharmaceutical or cosmetic industries.

This booklet for initial environmental assessment covers aquaculture projects consisting of farming/cultivation and harvesting of fish, shellfish, molluscs (shells, snails) or seaweeds. Farming of crocodiles and turtles are also forms of aquaculture, but will not be dealt with in this booklet. In addition to the aquaculture farm as such, a project may include facilities for the production of fry and feed. Some aquaculture projects may also require facilities for the processing and distribution of the aquaculture products. These can be separate projects or sub-projects of a major aquacultural investment. Aquacultural investment may also entail measures in terms of training, research, legislation, consulting, marketing, administration and establishment of institutions.

The choice of technology, scale and intensity of cultivation will vary a great deal, and will be decisive for the environmental and socio-cultural impacts of aquaculture. Aquaculture projects may vary as to stocking of organisms, preparation of the production areas and the degree of feeding, fertilization and medication. The farm organisms can be restocked at different stages of development. For example, they may be wild fry which have been collected for further cultivation. In other cases the fry are farm-cultivated. Import of fry from other districts or countries is another alternative. Preparing the production areas may involve making enclosures in bays, lagoons, lakes, ponds or man-made ponds/reservoirs, the building of artificial embankments and basins, and the use of cages. A cage is an open, free floating net attached to a framework for use in both freshwater and saltwater environments (cf. chapter 2).

It is common to distinguish between extensive, semi-intensive and intensive production, depending on the degree of feeding and fertilization in the farms. Extensive farming involves no feeding and no, or minimal, fertilization, semi-intensive some supplementary feeding and fertilization, and intensive steady supply of feed and fertilizers. The more intensive the production, the higher is the density of farm organisms in the farming medium. In intensive farming systems, aimed at a high production, the density of farm organisms is often very high. Moreover, intensive systems are based on the cultivation of only one species (monoculture). The environment therefore becomes very different from a natural one, and the farm organisms may be exposed to stress and a greater susceptibility to diseases. Accordingly, the need for medication will increase in proportion to the degree of intensification. In extensive and semi-intensive farming there will rarely be a need for medication, whereas drugs such as antibiotics, fungicides and parasiticides are necessary in intensive systems.

In developing countries there are intensive, semi-intensive as well as extensive farming systems. Extensive and semi-intensive systems are currently the most common. In several places, however, there is growing interest in the development of intensive systems. Generally speaking, extensive and semi-intensive aquaculture can be said to be more easily adaptable to a particular environment, and the potential environmental problems will be fewer and less serious than those caused by intensive aquaculture.

Extensive and semi-intensive farming systems are often technically simple, but can at the same time be biologically complicated. Several species are often cultivated simultaneously (polyculture), exploiting different ecological niches. In the countryside semi-intensive systems often combine agriculture and aquaculture. In this way agricultural refuse, manure from domestic animals etc. are utilized in fish-pond production. Fish farming can also be based on other supplies of nutrients such as sewage and septic waste. Extensive and semi-intensive systems are generally labour-saving and less capital-intensive, many have been operated for several generations and are well adjusted to local conditions. The development of extensive and semi-intensive systems is commonly geared towards production for local consumption. Generally, therefore, no major development of processing and distribution systems is required.

The cultivation of molluscs and seaweeds takes place extensively. Molluscs, for example, will take advantage of the local production facilities by filtering particles from the waters. Such a farm may therefore, to a certain extent, serve as a purifier plant, as the shells filter small organic particles. The organisms to be cultivated are restocked or planted, for example on devices where the organisms can fasten themselves.

Historically intensive farming systems are relatively young. They have been in the process of development since the turn of the century, but have received a powerful impetus in the last decades. Primarily it is carnivorous (carnivore) species of fish and shellfish that are being cultivated intensively.

The requirements as to control and management of the feeding, medication, water quality and volume are higher than those applying to other systems. Further, the hygienic requirements are high, since the risk of pollution from drugs, nutrients and organic matter is high. Regular maintenance and cleaning of the farms is necessary. Intensive farming often requires a considerable capital investment and the availability of a trained and permanently employed workforce. Nevertheless, the forms of farming are not especially labour-intensive. They often involve a great increase in production and will generally require the establishment of facilities for reception, processing and distribution of the farm products.

The development of a reception, processing and distribution apparatus for aquaculture production requires land and a stable supply of energy (oil and electricity) and high-quality water. This especially applies to modern methods of preservation such as icing and freezing, but traditional methods of treatment, e.g. smoking, also depend on an ensured supply of energy. Less energy-consuming methods, e.g. drying and salting, may be relevant alternatives. An increased investment in aquaculture, moreover, requires a sufficient supply of building materials, e.g. wood for the building of cages or pens.

The handling of large amounts of farm products in a restricted area can cause problems with the treatment of waste (cf. the booklet for initial environmental assessment of waste treatment and disposal). Waste from e.g. the handling and processing of fish consists of easily decomposable organic matter which accounts for between 5 and 30 per cent, and in special cases up to 70 per cent, of the raw material, depending on the degree of processing. This waste is actually a resource which may yield a series of valuable products, e.g. feed, fish meal, fish oil, big-gas, fertilizers etc., or form a basis for the production of more specialized organic products.

As already mentioned, a major development of aquaculture is likely to lead to the development of several associated functions. In such cases, one can also consult the checklists and/or booklets for initial environmental assessment of industry, transport, development of densely populated or urban areas etc..

If the aquaculture project comprises training and/or the development of administration and institutions, environmental aspects and the question of environmental competence should be given careful consideration.

2 The environment affected by the project

Aquaculture is carried out in different kinds of ecosystems comprising all water types. Some tropical ecosystems affected by aquaculture are vulnerable to encroachments and are themselves conservation-worthy. Furthermore, aquaculture farms will in many cases affect environments already exploited for other purposes, causing conflicts with other activities over the utilization of land and water resources. Below is an overview of the different ecosystems and environment types in tropical areas and developing countries where aquaculture is being practiced, as well as the most likely forms of aquaculture in the respective areas:

1) Freshwater areas:

Freshwater environments account for the most common aquaculture environments in most developing countries. They comprise farming of various species of fish and freshwater shrimps. Freshwater farming comprises a series of different environments and forms of farming. The most common are:

Lakes: These comprise natural lakes as well as large man-made lakes and reservoirs. Semi-intensive and intensive forms of farming are the most common, and these are carried out both in shallow waters by means of enclosures or by the use of pens. Transitional forms towards fishery also occur (cf. booklet for initial environmental assessment of fisheries) where fish are restocked and caught as in ordinary fishing. The farms are run by farmers, fishermen as well as by more affluent layers of the population.

Large man-made ponds: Many extensive and semi-intensive farms for fish farming consist of relatively large, shallow ponds (c. 1.6 hectare or more) which can be drained and treated before the restocking of new farm organisms. These are often located in areas well supplied with nutrients and organic matter. The surrounding vegetation is often used as feed for herb-eating fish (herbivore). The ponds are usually located in agricultural areas and are commonly run by local farmers and/or fishermen.

Small man-made ponds: These ponds (smaller than 1.6 hectare) form the basis of a variety of types of extensive and semi-intensive farming, often in combination with other activities such as animal husbandry (e.g. ducks, hens) and agriculture. Farming in these ponds is often biologically complicated as several species are often cultivated simultaneously (polyculture). Such farms are usually run by local farmers. The farming of freshwater shrimps, on the other hand, is an intensive form which takes place in small ponds, usually managed by well-funded contractors.

Natural ponds, rivers and major canals: Such water bodies can be exploited for extensive and semi-intensive farming. This is done by means of enclosures and net pens. The farms are usually run by local people.

Rice fields and irrigation canals: These can, to a certain extent, be used for fish farming. Wild fish can be enclosed within the rice fields or restecked systematically in a common culture which can be utilized by the rice as well as the fish. The introduction of herb-eating fish controls the growth of weeds; some fish also eat vermin living on and off the rice plant or other local species.

2) Marine coastal areas:

Aquaculture in marine coastal areas takes place in both saltwater and brackish water, and comprises a series of different forms of farming.

a) Saltwater:

Farming systems in saltwater are different with respect to choice of technology, species and environment. The most common forms are:

Fish farming in cages, pens and pen culture (bottom of the pen is formed by the lake or sea bottom) and enclo-sures: These are intensive forms of farming that exploit areas providing the farms with natural protection e.g. boys, inlets etc. The development of sea-cage farms with large, solid cages currently enables farming in more open and exposed localities, which greatly reduces competition with other user groups. These farms are commonly run by well-funded contractors.

Intertidal forming of shells, snails and seaweeds: These are extensive forms of farming that utilize areas offering natural protection against rough weather. The farming may consist of sea-floor cultures whereby the shells are scattered directly on the sea floor in the tidal zone or deeper down. Another form involves the placement of various types of stationary racks for the farming of seaweeds, or racks on which baskets for the farm organisms can be hung. A third type involves hanging cultures whereby the organisms hang freely in water in ropes and tapes from rains and sticks. Areas used for this kind of farming are often attractive for other activities as well, so that conflicts may occur between different user groups. Depending on the size of the farm, these forms of farming are practiced both by the poor and the more affluent parts of the population. intertidal farming of shrimps and fish: These are intensive and semi-intensive forms of farming. The areas being used can be marine lagoons and ponds or tanks on land which are situated in the tidal zone or nearby. Such forms of farming can in many cases affect mangrove swamps. The farms are usually operated by the affluent part of the population.

Restocking of fish - sea ranching: This involves restocking of fry in order to consolidate an existing stock of fish in naturally restricted areas, e.g. a bay, which is subsequently harvested as in ordinary fishing (cf. booklet for initial environmental assessment of fisheries).

b) Brackish water:

Farming in brackish water usually takes place in estuaries, which provide the farms with natural protection, and mangrove swamps, where the salinity is conducive to cultivation of both shrimp and fish species by means of methods that are equivalent to those described under saltwater above. One often finds large embankment ponds where the entrance can be controlled with a sluice, and which take advantage of the tide. The methods can be intensive, semi-intensive or extensive.

Ecosystems such as mangrove swamps and coral reefs are especially vulnerable to pollution and technical encroachments. They may, in themselves, be preservation-worthy types of nature, as well as being vital for the reproduction and growth of economically important species.

Many tropical water bodies - freshwater, brackish water and saltwater - are extremely low in nutrients. The nutrients are largely bound up with the existing flora and fauna. By a steady supply of nutrients, as in semi-intensive and intensive farming, the ecosystem may acquire a higher substance value. Besides, this may improve the production of other useful plants and animals. Yet problems of pollution and eutrophication in watercourses and coastal areas are more frequently the case (cf. chapter 3.3).

Tropical water bodies are often subject to considerable evaporation. In freshwater environments, therefore, it is important to ensure an adequate and stable water supply to the farms. In dry areas or areas with little rainfall, limited ground-water resources are sometimes used for aquaculture. Such a situation may require a survey of available water sources and other hydrological conditions before aquaculture farms are developed (cf. chapter 3.5). The water temperature can also be decisive with respect to which species can be cultivated.

Tropical soil often contains pyrite, which makes the water acidic and unsuitable for farming. Areas which have already been used as embankment ponds can be treated by covering the dam floor with special tarpaulins, or by adding calcium to the water. This is resource consuming, however, and in order to avoid such misplacement of aquaculture farms, soil tests should be taken prior to a development.
The local social conditions relating to a project may vary greatly from place to place. In some areas aquaculture may have been practiced for generations, having become part of the local culture and tradition, whereas in other areas it has never been practiced. Large parts of Asia have long traditions of aquaculture, and it is more common there than in Africa and Central America. Farmers in developing countries are a heterogeneous group ranging from poor smallholders with a few fish in a small embankment pond to multinational companies engaged in sophisticated and intensive aquaculture. Between these are relatively affluent farmers and other rural and urban enterprisers.

In connection with the planning of aquaculture in areas where it has never been practiced, one should be aware that the local population may not have title to land or water. Such rights are often allocated according to traditional and complex arrangements, and may involve that a farmer, for example, has only limited or seasonal access to land and/or water resources (cf. chapter 3.6).


This survey covers both direct and indirect environmental impacts. It is often difficult to distinguish clearly between these two types of impacts. The direct impacts may derive directly from certain properties of the aquaculture project itself. The indirect impacts may result from other types of activities in association with the project, e.g. processing. Indirect environmental impacts can also occur if the project alters socio-cultural conditions in the local community, e.g. through changes in the power structure.

3.1 Introduction of new species

In some cases it may be desirable to farm species that are not naturally existing in the area. Should faults occur, however, or should the farm be wrecked, this may cause new species to be spread into the environment. Generally speaking, one will have to expect some individual escapes from such farms. It is difficult to draw reliable conclusions concerning the way these individuals will function in the ecosystem. However, there is a risk of initiating an uncontrollable breeding process. This can impact the natural existence of conservation-worthy or commercially viable species. These may either be outcompeted or their natural means of existence may be spoiled. Moreover, there is widespread concern that imported organisms may replace local and genetically better adapted fish stocks and variants. Further, there is also a risk of genetic changes in naturally existing fish.

Another impact which is often associated with the spreading of new species, is the spreading of fish diseases. New species or farm organisms which have been collected from other geographical areas, may carry bacteria, viruses and parasites which then spread and cause diseases. This can lead to depletion or extermination of valuable species. One should be aware that parasites, bacteria and viruses that are harmless in some areas can cause catastrophes if transferred to a different environment.

It is also worth noting that diseases that are harmless in a natural environment may have far more favourable conditions for growth in an aquaculture farm, especially in farms with a high density of organisms. As a result, intensively run farms (cf. chapter 1) require a supply of therapeutic chemicals (antibiotics, fungicides) and antifoulants which can potentially cause pollution (cf. chapter 3.3).

3.2 Impacts on the ecosystem, and the natural and cultural landscape

Technical installations, pollution, spreading of new species and spreading of fish diseases may, alone or combined, cause such drastic environmental impacts that the original ecosystems are changed. This can affect other forms of economic exploitation of these areas. The occurrence and the produced amount of other utilizable species can be altered, and the suitability of the water body for other uses can be changed.
Special care should be taken if the farm is situated in, or near, vulnerable or conservation-worthy ecosystems, e.g. mangrove swamps or coral reefs. Mangrove swamps have in some places been under great stress, because they are attractive for shrimp and oyster production. Great harm can be done to their natural function as propagation and growth areas for other valuable species.

Large aquaculture farms in marine coastal areas can be so attractive to sea birds that they may migrate from their natural habitats.

The scope of likely impacts on the ecosystem depends on the scale and intensity of the project. Generally speaking, extensive and semi-intensive aquaculture projects are more adaptable to the ecosystem than are the intensive ones.

Large aquaculture farms may entail considerable encroachments on the landscape.

The visual character of the natural and cultural landscape may alter so that it becomes less attractive for recreation and tourism etc.. Historic remains, buildings and other landscape elements that are important to the local population can also be affected. In order to reduce the impacts on the landscape, one ought to make values of landscape part of the planning process with respect to mitigative and reconstructive measures.

3.3 Pollution and waste disposal

In farms directly connected to sea or watercourse, artificial feeding or supply of fertilizer or organic matter can lead to eutrophication in the water body. The likelihood of such problems depends on the choice of locality and its physical surroundings: bottom conditions (mud, sand, rock etc.), currents, light, depth, supply of oxygen and climate. Excessive fertilization does not always cause problems for other user interests. In fact, a moderate stress may, occasionally, be beneficial, whereas in cases of great stress in vulnerable environments the impacts can be severe.

Excessive fertilization of freshwater can cause growth of algae and other aquatic plants, which makes the water unsuitable as drinking water. Furthermore, this may hinder fishing and boat transport. In cases of great stress, periodical or constant deoxygenation in the bottom layers may result, bringing damage to the flora and fauna, and problems with smell. This type of pollution can endanger the productivity of aquaculture farms if the polluted water body is also utilized for this purpose. With regard to saltwater, it is important to consider what impacts the supply of nutrients will have on vulnerable ecosystems and on the possibility of producing other valuable species of fish, shellfish and molluscs. In addition to the risk of eutrophication due to feeding and supply of nutrients, faeces from farm organisms is a potential pollutant. This especially applies to intensive fish farming, since the sea floor under the pens can be polluted.

In semi-intensive closed farms and isolated ponds, one will deliberately try to create a state of excessive fertilization in order to improve the supply of nutrients for the flora and fauna, which in turn constitute the feed-base for the farm organisms. For example, this may be done by supplying organic offal, waste water etc.. This will in many cases be a sensible form of resource utilization. However, control of the supply is necessary. Environmental stress caused by waste water or the supply of agricultural refuse containing pesticidal remnants etc. can cause pollution which affects the farm output and the suitability of the farm organisms as human food.

Extensive use of drugs to prevent diseases in farm organisms, as commonly practised in intensive farming, can pollute the surroundings. Many types of antibiotics are not easily broken down in the farm organisms and will be spread to wild fish and other naturally existing organisms, e.g. sea birds and sea mammals. Bacteria, moreover, can become resistant so that new types of antibiotics need to be introduced. The long-term environmental impacts of these drugs are unpredictable.

In semi-intensive and intensive farms, therapeutic chemicals are generally used. Chemicals can also be supplied to the environment from other aspects of the operations, e.g. in connection with the removal of unwanted vegetation or algal growth from net pens etc. In addition, insecticides are sometimes used to limit the spreading of malaria, for which some aquaculture farms offer favourable growth conditions (cf. chapter 3.4). Fish being dried or stored is sometimes sprayed with pesticides to avoid damage from insects. Use of chemicals should be avoided. Nevertheless, if chemicals are to be used, the choice of chemicals should be decided on the basis of their decomposability and capacity for being absorbed and metabolized in fish and other farm organisms. Possible damage to humans and animals as well as impacts on the aquatic ecosystems should be carefully considered (cf. the booklet for initial environmental assessment of the use of chemical pesticides).

Pollution problems can also arise in connection with handling, storage and transport of fish and other farm produce. Concentrated handling and processing can create a waste problem. This waste will consist of perishable organic matter. If stored on shore, it can smell and attract insects, rats, birds etc.. Insects and offal-eating animals can spread diseases to the local population. One should be especially alert to the possibility of the spreading of parasites which have fish as an intermediate host. Sea birds can carry infections from rubbish heaps and drinking-water sources. If the offal is dumped into water, it can cause eutrophication, and deoxygenation in the deep-water layers if there is insufficient circulation in the water. Deoxygenation can have fatal effects on local fish and cause problems with smell. The organic offal contains valuable nutrients and is thus a potential resource (cf. chapter 1).

3.4 Spreading of diseases to humans

If the project involves the building of artificial ponds and canal systems, this may create improved conditions for the propagation and spreading of water-borne diseases. Stagnant waters can create favourable conditions for the propagation of bilharzia and malaria. Patogens are often widespread in both shallow freshwater areas and shallow salt/brackish water areas.

One should take great care if the production is based on sewage or manure and latrine excrements. Bacteria and other patogens will spread and can pose a health risk to both farmers and consumers.

The use of chemical pesticides (cf. chapter 3.3) should be considered against the potential risk for humans. Use of antibiotics must be under control so that remnants in the farm produce are avoided. Spreading to wild fish and other naturally existing organisms is likely to occur. Yet these organisms are rarely tested even if they may, for periods of time, contain considerable amounts of antibiotics.

3.5 Increased demand for water and energy

Freshwater farming of fish or other organisms requires stable supplies of high-quality water, which is often scarce. One should be particularly alert to the fact that the water supply may vary substantially both seasonally and annually. With respect to projects that require large amounts of water, one should make a survey of water sources and estimate the water supply. In case of permanent or periodical scarcity of water, conflicting demands may arise between aquaculture and irrigation or supply of drinking water. Tropical water bodies are often exposed to considerable evaporation, which in turn leads to an increased demand for water supplies. If the evaporation is high, the pollution of the water will be more concentrated. It is possible to save water by adding oxygen to ponds by means of ventilators. The accessibility of technology and expertise, in addition to profitability, are decisive factors. In dry areas, ground water is generally used for aquacultural purposes. However, excessive exploitation of ground water can cause problems owing to a lowered ground-water table and increased salinity in the water.

Smoking of fish requires wood or other kinds of fuel. If there is a substantial increase in the amount of fish to be smoked, one must consider whether the required fuel supply is available, and how to acquire it. If wood is also used for other purposes, conflicts may arise. The use of wood and bamboo for building cages and stationary enclosures can put pressure on limited resources. Freezing and ice production, and various other industrial processes, require electricity and/or oil (cf. the booklet for initial environmental assessment of industry).

A project may lead to competition for scarce water and fuel resources. On the other hand, the project may lead to improved water and fuel supplies in an area in which such supplies were originally insufficient. This can bring about improved living conditions for large groups of people. However, the use of water can also have environmental impacts which need to be assessed (cf. the booklet for initial invironmental assessment of water supplies).

3.6 Impacts on traditional ways of life and utilization of natural resources

Aquaculture projects may create changes in traditional ways of life and utilization of natural resources. Generally speaking this can occur in two ways: a) Those impacts a project may have on the local ecosystem may require that the local, traditional utilization of natural resources must be rearranged. b) The direct impacts of a project on the local socio-cultural and socio-economic conditions may indirectly create long-term environmental impacts through changed natural resource utilization.

Fish farmers in developing countries are a heterogeneous group (cf. chapter 2). Basically, aquaculture projects can range from small-scale farming carried out by locals in the countryside to intensive farming in e.g. marine coastal areas run by well-funded contractors. The relevant project areas can be divided into two main categories: areas where aquaculture has been practiced for generations thus having become part of the local production and culture; areas where aquaculture has not been practiced previously.

An aquaculture project which does not consider the economic, social and cultural conditions of the project area or its vicinity may easily create conflicts. Generally speaking, extensive and semi-intensive forms of farming are more adaptable to local conditions than intensive ones, partly because intensive farming requires a considerable investment of capital. Adaptation will be easier in areas where the local population is familiar with fish farming. The population in other areas is likely to regard aquaculture as a risky trade requiring new input and know-how. Due to local traditions and power structures, the local population may not have title to land or water, or have merely seasonal access to these resources. The choice of farm species, moreover, should be carefully considered in relation to local traditions and diets.

Aquaculture can create conflicts with the local population's use of land, water and other natural resources. Transport and traffic in bays and other coastal areas can be hindered. Areas utilized for the purposes of agriculture, forestry or animal husbandry can be affected. Conflicts with existing fisheries may arise. Fishing and fish handling are traditionally carried out by certain groups of a population, whereas it is often different groups that adjust to a prospective new trade. Aquaculture projects can change the need for labour and training. Transition to a new technology and trade can alter the traditional division of labour between men and women. The possibility of conflicts with other population groups within the project area is also worth considering. Aqua culture is not particularly labour-intensive. Accordingly, it takes large intensive farms before migration into the area, on account of the project, will develop into a potential environmental problem. On the other hand, aquaculture farms can lead to local migrations causing potential land-use conflicts and increased pressure on the natural resources.

3.7 Impacts of new activities, and already existing activities

Investments in aquaculture can initiate the development of other activities such as industry, transport, water supply etc.. Such developments can indirectly lead to environmental impacts which should be assessed.

In addition, already existing, or planned, activities may have environmental impacts on aquaculture and aquaculture projects.

For example, waste disposal and pollution from industry, agriculture and densely populated areas may reduce the quality of the water being used by the farms.

An overview of potential environmental impacts of new and already existing activities can be found by consulting the booklet "Checklist for initial screening" and/or the booklet for initial environmental assessment of the category in question.

4 Relevant literature

Barnabe, G., 1990: "Aquaculture". Vol. 1 & 2. Ellis Horwood Limited, England.

Beveridge, M., I 1987: "Cage Aquaculture". Fishing News Books Ltd., British Library CIP Data, England.

Braaten, B., 1992: "Impact of pollution from aquaculture in six Nordic countries. Release of nutrients, effects, and waste water treatment". In European Aquaculture Society Special Publication No. 16. Norwegian Institute for Water Research (NIVA).

Cross, D., 1991: "FAO and Aquaculture: Ponds and Politics in Africa". The Ecologist, Vol. 21, No. 2, March-April 1991.

Danida, 1989: "Environmental Issues in Fisheries Development". Danida/Ministry of Foreign Affairs. Copenhagen, Denmark.

FAO/UNDP, 1990: "Regional Seafarming Resources Atlas", Bankok, Thailand.

NORAD, 1989: "Environmental impact assessment of development aid projects: Checklists for initial screening of projects". NORAD, Oslo, Norway.

Pillary, T.V.R., 1990: "Aquaculture: Principles and Practices". Fishing News Books, Blackwell Scientific Publishing Ltd., Oxford, Cambridge, London.

Pullin, R.S.V., Shohadeh, Z.H., 1980: "Integrated Agriculture Aquaculture Farming Systems". ICLARM, Manila, The Philippines.

Pullin, R.S.V., 1989: "Third World Aquaculture and the Environment". NAGA, The ICLARM Quarterly. January 1989.

Skagen, Kaj, 1990: "Requiem for Salmo Salar". In Samtiden, No. 2, 1990. Aschehoug, Oslo, Norway.

UNEP, NORAD, FAO, 1987: "Thematic Evaluation of Aquaculture". Rome, 1987.

UNEP, 1990: "Environmental Guidelines for Fish Farming". United Nations Environment Programme, Nairobi, Kenya.