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09 Jul2006

Overstory #174 - The role of trees in aquaculture systems

Written by Nick Pasiecznik.

Summary

There are numerous instances of the intentional co-management of trees and aquatic organisms, though there are only limited specific studies on these interactions. Also, in addition to the direct interactions of forests, plantations and orchards trees on aquaculture, the use of tree products is widespread, as wood, fibres, food, poisons and other chemicals. On both micro and macro scales, there are many ecological interactions between trees and aquaculture. Trees play important environmental roles, ameliorating soil chemical and physical structure, shade and little fall, reducing soil erosion, increasing water infiltration, flood limitation, etc., that impact directly, or indirectly, on water quality and quantity. Thus, forest, plantation and orchard management practices and systems will clearly affect local and regional water bodies, and subsequently aquaculture activities. This paper aims to draw attention to the valuable role that trees play in aquaculture systems, either as consciously managed combined 'silvoaquaculture' systems, or incidentally via unmanaged environmental interactions.

Agroforestry and silvoaquaculture

The management of trees with agriculture gained prominence in the 1970s, and was given the name 'agroforestry'. An international centre, ICRAF, now the World Agroforestry Centre, was established to further research and development in this new field. Early work concentrated on definitions and system classification, with most working on the triangular model of trees-agriculture-livestock and their interactions. Very few early models considered agroforestry to include aquaculture, and only one gained any recognition, that which appeared as a circular model divided into four quarters (trees-agriculture-livestock-aquaculture). The triangular-terrestrial model gained prevalence, and the emphasis of agroforestry to this day has been on trees on farms and pastures. However, systems integrating aquaculture are documented, known by a variety of names, such as aquasilviculture, agrosilviaquaculture, etc.

Classification of silvoaquaculture systems

Silvoaquacultural systems, like other agroforestry and land-use systems, can be classified by components, environment (climate, soil, topography, etc.), management applied (e.g. intensive, extensive), geographic location, organisation of the tree component in space and time, etc., or any combination of these, to suit the needs of the classifier or user. For the purposes of this paper, four principal system types have been identified, classified by the land-use system in which they are found, i.e. 'natural' forest, plantation, silvoarable or agrosilvopastoral systems, further divided by diverse criteria solely as a means to group similar sub-systems.

1) Aquaculture under natural forests

Characteristics of these systems are variable water levels, as few trees tolerate permanent submergence under water. Aquaculture systems operating include fishing of unmanaged ('wild') stocks, mainly with nets, lines and spears; also some stock-rearing in pens and cages. Examples of such systems are:

  • Fisheries under flooded rainforest, e.g. in the Amazon in Brazil (Werder, 1999) and Guyana (Gerrits et al., 1996), or in South-East Asia, such as Cambodia, where Grunewald (1993) analysed the relationships between flooded forests, fish and traditional fishing techniques and the effects of pesticide use on fish resources was noted.
  • Mangrove forests and their hinterlands, e.g. West Africa, South-East Asia, South Asia, such as in Sri Lanka (Dharmasena, 2002).

2) Aquaculture under plantations

Characteristics of these systems are the addition of aquaculture production to an existing plantation system, often with notable nutrient exchanges between the tree and aquatic components, leading to a more efficient, diversified and profitable systems. Examples include:

  • Fisheries under plantation crops, e.g. coconut in India (Maheswarappa et al., 2000), and Indonesia, such as in tidal swamp areas where coconuts are combined with fish, prawn, duck, crab or lowland rice production (Darwis, 1990), also under other humid tropical plantation crops such as oilpalm in Africa or arecanut in India.
  • Flooded plantation forests, e.g. fisheries in the southern USA under pine plantations (Pinus spp.).
  • Ponds in plantation forestry, e.g. planting trees in ponds, such as baldcypress in crayfish ponds in Louisiana, USA (Conner et al., 1993), or establishing ponds in plantations, e.g. in China (Yu et al., 1990).

3) Aquaculture in silvoarable systems

Characteristics of these systems are the pre-existence of intensively managed agriculture as the principal component, with the inclusion of trees serving secondary productive and/or protective functions, and aquaculture as another peripheral activity leading to increased diversification, nutrient transfers and system efficiency. A livestock component may be present, but is less important, often being only the grazing of fallows, etc. The aquaculture component can be managed concurrently with the crop or between harvest and land preparation, and this temporal sub-classification is used below. Examples included:

  • Fisheries in rice paddies, with trees as shelterbelts or hedges along field margins and/or irrigation channels, e.g. in South and South-East Asia.
  • Temporary ponds established outside of the cropping period, e.g. South-East Asia and India, such as the leasing of land for prawn farming in rainfed systems during rabi and summer seasons in the coastal regions of Karnataka (Naik and Sastry, 2001).
  • Aquaculture carried out in the irrigation channels, canals or storage ponds themselves.

4) Aquaculture in intensive agrosilvopastoral systems

Characteristics of these systems include the presence of often very small land-holdings with a high diversity of crops and animals in multi-layered and highly integrated systems. The aquaculture component is mostly included in small ponds. Such systems are often highlighted as being some of the most productive and resilient land-use systems in the world, and have been widely promoted as solutions to problems of sustainability and environmental degradation. Livestock are essential components, with ruminants, pigs and poultry being common, also other small ruminants such as rabbits (Wang, 1988), or even crocodiles may be incorporated (e.g. Baumer et al., 1990). Examples include:

  • Homegardens, e.g. in southern India (Karnataka, Kerala, Tamil Nadu and the Andaman Islands, Pandey et al., 2002), and Indonesia
  • Dyke-pond systems, e.g. China, such as in the Zhujiang (Pearl river) delta southeast China with an integrated, intensive agriculture system involving fish ponds, mulberry dykes and sugar cane dykes. Ruddle and Zhong (1988) cover in much detail the different components and variants, including rearing of fry, production ponds and fish cultivation in the ponds and mulberry, silkworm, vegetable and sugarcane subsystems on the dykes, and the integration of dyke and pond. Cut flower and banana production has begun to replace mulberries as the world market for silk has declined (Mo, 1988).

The use of tree products in aquaculture

It is not within the scope of this paper to explain in detail the indirect relationships between trees and aquaculture resulting from the use of tree products in the production, harvesting and post-harvest processing of aquaculture products. However, it is enough to say that there is long history of use, and a co-evolution of certain aquaculture practices dependent upon the nature of the tree products available.

Examples of the varied use of tree products in aquaculture include:

  • wood for boat building,
  • tree products (foliage, fruit, processing residues) as an aquaculture feed,
  • bamboo as a substrate in periphyton-based aquaculture systems,
  • reeds (perennial woody species) for water filtration/purification,
  • branches for fishing rods/poles, spears, clubs, drying racks, cages, floats and transporting fish,
  • branches and other woody material as structures for spawning or the raising of fry,
  • firewood for post harvest treatment (smoking) and cooking,
  • tree fibres for nets and fishing lines,
  • tree extracts for preserving fishing nets,
  • tree extracts as piscicides/fish poisons,
  • tree extracts for treating fish diseases.

Selected examples of the use of tree products in aquaculture are, however, important in demonstrating the interactions in silvoaquaculture systems, and as such, some are covered in a little more depth.

These are:

  1. Tree foliage and fruit as a fish fodder,
  2. Branches as brushparks, and
  3. Tree extracts as piscicides and in treating fish diseases.

1) Tree foliage and fruit as a fish fodder.

The use of foliage and fruit from trees is an important aspect in silvoaquaculture systems. Agricultural residues such as from groundnut and soya are widely used, and their value as fish food is well known and have been commonly used for centuries. Some tree fodders are also used routinely in some systems. A number of agroforestry species, mainly legume trees, that have been widely introduced and planted around the world during recent decades have also been assessed for the potential use in mixed fish systems, though few have proved very successful. Recent studies showing benefits include the use of Cassia fistula (Adebayo et al., 2004), Hevea brasilensis (Alegbeleye et al., 2004), Moringa oleifera (Richter et al., 2003), Parkia biglobosa (Akegbejo Samsons and Ojini, 2004) and Shorea robusta (Mukhopadhyay and Raj, 1999).

2) Branches as brushparks.

The conscious incorporation of woody material into a water body allows for improved fish production, due to, it is thought, provision of sheltered and protected areas for fish to spawn, and fry to develop. In Malawi, such 'brushparks' were found to significantly improve aquaculture production (Jamu et al., 2003), simulated woody matter increased salmon production in the USA (Culp et al., 1996), and brushwood deposited in the waters of Salford Docks, Manchester, UK, increased the spawning of several fish species (Nash et al., 1999).

3) Tree extracts as piscicides and in treating fish diseases.

The two most commonly studied extracts are from neem (Azadirachta indica) and oil of cloves. Neem has been found to be an effective treatment for numerous ailments of mainly finfish in culture, including Cyprinus carpio (Harikrishnan et al., 2003) and Oreochromis mossambicus (Logambal and Michael, 2000), where the observed immunostimulatory property of azadirachtin was seen to have implications in the maintenance of finfish health in freshwater intensive aquaculture practices. Clove oil has also been used effectively as an anaesthetic, for eels (Walsh and Pease, 2002) and salmon (Woody et al., 2002), and guava extract (Psidium guajava) was the most effective extract from 16 species in Thailand against fish bacteria (Direkbusarakom et al., 1998). However, many plant extracts that may be used for positive effects on fish health, may be toxic or lethal at higher concentrations, or on different aquatic species. Neem, for example, has been found to be acutely toxic to freshwater prawns (Das et al., 1999), and Nasiruddin et al. (1997) concluded that extracts of neem seed kernel might be useful in controlling predatory or undesirable fish species in the nursery, rearing and stocking ponds of commercially valuable fish species. Many other tree extracts have both antimicrobial and cytotoxic effects, such as that of carob (Ceratonia siliqua) on shrimp (Kivcak et al., 2002). Concerning piscicides alone, very many plant extracts are recorded as having this quality, and numerous studies from around the world, especially on ethnobotany, identify such species (e.g. Singh and Singh, 2002; Sambasivam et al., 2003).

Impacts of aquaculture on ecosystem

Economic impact

There are numerous and substantial benefits recorded, both economic and environmental, resulting from existing, integrated systems involving aquaculture and tree-based farming, forestry and orchards (e.g. Huang et al., 1987; Lightfoot, 1990). Aquaculture provides an additional income in tree-based production systems, also diversifying output and mitigating risks associated with crop failure or livestock diseases, and the integration of aquaculture is being increasing promoting as a means towards sustainable agricultural development. There also appears to be great potential in developing such systems, from further study and suitable adaptation and adoption of relevant aspects, with complementary advantages to all productive components. For example, in Australia, aquaculture is suggested as part of new integrated systems incorporating trees, particularly to increase production in, and to ameliorate conditions in land already degraded by inappropriate farming practices, and experimental experience appear to show economic viability (Ingram et al., 2000).

Also, wastewater from aquacultural systems is being increasing employed in tree production, both as a means to decrease effluents and pollutants from aquaculture, and to increase tree growth. For example, D'Silva and Maughan (1994) integrated wastewater from fish culture with the growing of ornamental mesquite (Prosopis glandulosa) in the USA, allowing tree production in half the time required if well water was used, and Jungersen (1991) found similar benefits for plant production from the wastewater from eel farming.

Environmental impact

Aquaculture activities may impact heavily upon local environments. One way is by increased peripheral resource use, such as the need for wood for the smoking of fish, which has for example, lead to significant deforestation in parts of Malawi, and the need for fishing communities to plant trees themselves (Mills, 1994). Other environmental benefits, such as the use of aquaculture wastewater in tree production (e.g. Jungersen, 1991; D'Silva and Maughan, 1994) and aquaculture as a means for land reclamation (Ingram, 2000) are as described in the section on Economic impact, above. Other benefits may involve more effective nutrient cycling, or even effects on local fauna, with potential economic benefits. One interesting system of merit from China involved hanging lights at night over ponds established in commercial plantations, which attracted large numbers of insects, many of which dropped onto the water. This had the double benefit of reducing the forest pest burden of the plantation species, and significantly increased the growth of fish in ponds with night lights as compared to the control. This one example of novel integration of forestry and aquaculture leading to environmental and economic benefits, but there are surely many more in existence around the world, probably very locally, and many other systems may profit from them were they more widely known .

Social impact

There are limited possibilities for aquaculture to have social impacts on forests, plantations or orchards. One means is, however, though tourism, such as angling as a part of recreational forestry, on forest rivers and lakes, or in coastal environments as part of fully integrated systems. Examples include Kenya (Baumer et al., 1990) and India (Taylor, 1993).

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Original source

This article was reprinted with permission from the author and publisher from

Pasiecznik, N. 2005. Silvoaquaculture datasheet. In CABI, Aquaculture Compendium.

For more information about the Aquaculture Compendium contact CAB International Wallingford, OX10 8DE, UK Fax +44 1491 833508 E-mail compend@cabi.org

About the author

Nick Pasiecznik is managing consultant for Agroforestry Enterprises, specialising in research, development and training in agroforestry, drylands and timber processing, is a leading expert on Prosopis species. Other interests and experience include forestry, agriculture and land-use systems, organic production, invasive species and plant taxonomy.

Nick Pasiecznik Agroforestry Enterprises Villebeuf 71550 Cussy-en-Morvan France

npasiecznik@wanadoo.fr +33 (0)3 85546826

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