Aquaculture Systems and Species¹

(1)Simon Funge-Smith2 and Michael J. Phillips³

(1)FAO Regional Office for Asia and the Pacific,
39 Phra Athit Road, Bangkok 10200, Thailand
(2)Network of Aquaculture Centres in Asia-Pacific (NACA),
Suraswadi Building, Department of Fisheries,
Kasetsart University Campus
Ladyao, Jatujak, Bangkok 10900, Thailand

Funge-Smith, S. Phillips, M.J. 2001. Aquaculture systems and species. In R.P. Subasinghe,
P. Bueno, M.J. Phillips, C. Hough, S.E. McGladdery & J.R. Arthur, eds. Aquaculture in the Third Millennium. Technical Proceedings of the Conference on Aquaculture in the Third Millennium, Bangkok, Thailand, 20-25 February 2000. pp. 129-135. NACA, Bangkok and FAO, Rome.

Background

Sustainable improvements in technological aspects of aquaculture will not be achieved unless they are accompanied by appropriate policies that address the social and economic environment within which the aquaculture system is placed. The development of such systems must lie within the context of environmentally sound regulatory frameworks (e.g. systems providing for monitoring and enforcement, and good governance)

In the 21st Century, water resources will be at a premium, with water shortages expected after 2015. With such a pressure on this vital resource for aquaculture, business-as-usual scenarios will no longer be possible. Competition for this resource will increase with drinking water shortage expected to affect large populations by 2025. This important constraint will have a major bearing on how aquaculture can and will develop in the new millennium, and appropriate technologies and farming systems will be required to address this issue.

Within the context of this paper, the essential elements of aquaculture incorporate: the care of aquatic stocks; requires confinement or site allocation; isolation to varying degrees of the farmed stock from the external environment; allows for various levels of internal control of the system; and requires some form of ownership or contractual arrangement to that effect.

Aquaculture systems must be considered in relation to natural resource systems and human development circumstances within which reside.

Types of aquaculture systems

Systems and species

Aquaculture systems range from very extensive, through semi-intensive and highly intensive to hyper-intensive. When using this terminology the specific characterization of each system must be defined, as there are no clear distinctions and levels of intensification represent a continuum.

Farming systems are also diverse for example including:

• Water-based systems (cages and pens, inshore/offshore).
• Land-based systems (rainfed ponds, irrigated or flow-through systems, tanks and raceways).
• Recycling systems (high control enclosed systems, more open pond based recirculation).
• Integrated farming systems (e.g. livestock-fish, agriculture and fish dual use aquaculture and irrigation ponds).

Various aquatic organisms are grown in different ways including:

• Fish (ponds, polishing ponds, integrated pond systems).
• Seaweeds and macrophytes (floating/suspended culture, onshore pond/tank culture).
• Molluscs (bottom, pole, rack, raft, long-line systems also culture based fisheries)
• Crustaceans (pond, tank, raceway, culture based fisheries).
• Other minor invertebrates, such as echinoderms, coelenterates, seahorses, etc (tanks, ponds, culture based fisheries)

The phases of aquaculture include broodstock holding, hatchery production of seed, nursing systems, grow-out systems, and quarantining.

Together, this mix of intensity, culture systems, species, farming systems and different phase of culture create an extreme diverse collection of aquaculture systems and technologies.

Management interventions, infrastructure and support technologies

The management interventions, infrastructure and supporting technologies utilized in aquaculture include a wide range of activities, such as seed supply and stocking, handling, feeding, controlling, monitoring, sorting, treating, harvesting, processing and use of prophylactic measures.

Driving forces in the development of aquaculture

There are a number of factors, which drive aquaculture, again covering a spectrum from the needs of people (the provision of local employment, food security and the alleviation of poverty) to the needs of industries (with particular emphasis on profits, productivity and consistent-quality products).

Consequently, the requirements for sustainable aquaculture development will include both technological and people based approaches From this range of choices, the design and selection of appropriate culture systems can be made, which most effectively meets their needs and best, fits the opportunities and constraints of the local environment.

Future developments in systems and technology

Conventional pond systems

Shortage of water will become a limiting factor in many areas. Low input and extensive land based pond aquaculture is an inefficient use of fresh water – in warm, dry countries, a 1-hectare pond might lose 30,000 tonnes of water per annum through seepage and evaporation, yet produce only 1-2 tonnes of fish. Ponds must become more “intensive” with respect to water use. Aquaculture ponds can be integrated into water conservation and management systems and rainfed aquaculture can be an effective storage mechanism in areas that experience water shortages.

This means that millions of farmers will require education, technical assistance and effective extension of improved methods of aquaculture that utilize scare water resources effectively.

In some climates, flow-through systems can become more efficient through the re-use of heat energy, balancing the cost of water.

Crucial positive trends are the integration of pond systems (with other agriculture and water-using processes), reuse of water, and recirculation. For example, a recirculation system can achieve 150L water per kg of fish, or 40L per kg with a de-nitrification unit, although such systems may have limited transferability to the majority of aqua farmers.

Integration of aquaculture into other systems

Many “outputs”, often called “wastes” or “byproducts” of farming subsystems, can become basic inputs for other subsystems rather than just additive components of the overall farm economy.

There are examples of such integrated systems. Dual pond systems in Israel, for example, link irrigation water storage with aquaculture ponds, with seasonal transfers according to respective needs of irrigation and culture. Cages placed within reservoirs and ponds can also provide integrative processes on a small scale, making more effective economic use of the water resources as a whole.

Integration of livestock and aquaculture is common in many countries although in the future, the use of livestock or industrial effluents (e.g. sewage, heated water, process water) for aquaculture may raise ethical issues (moral and public health), that will have to be addressed. Specific issues are those of disease transmission and accumulation of toxic compounds.

There are alternative sources of water readily available for aquaculture arising from, for example, floodwater control in Bangladesh, or use of saline ground or surface water not suitable for irrigation or municipal consumption. Saline waters and land cover large areas in several Asian countries, and provide significant opportunities for aquaculture.

Recirculation systems

The uses of recirculation vary widely, from broodstock management, hatchery and nursery rearing, grow-out and quarantine holding. It is likely that use of recirculation systems in intensified commercial aquaculture will increase in future. There are many possible solutions, adaptable to specific local situations.

The PAS system for American catfish is one example. It combines an extensive set of channels within the pond, for water treatment, with a highly intensive growth enclosure. The very slow circulation with low energy requirement provides good control of pond environmental processes whilst conserving water.

The recirculation of water is not necessarily highly intensive. Shrimp farmers in Thailand are successfully using closed pond systems for removing the requirement for water exchange making efficient use of brackishwater and helping to reduce risks of introduction of shrimp pathogens to the farming system.

Active suspension ponds, which reduce the requirement for water exchange, have been demonstrated for tilapia in Israel and the USA and in shrimp culture in Belize Hyper-intensive recirculation systems have many advantages.

A well-designed recirculation system must be readily managed and competitive in terms of cost-efficiency, as such current applications are principally targeted at high value intensive aquaculture.

Hyper-intensive recirculation is currently particularly suited to Europe due to environmental pressures and the market for high value aquacultured species. As economic and resource conditions change in the future, alternative applications of recirculation are likely.

Technology issues in recirculation approaches:

There are a number of technology issues in recirculation technologies that include:

• Limited knowledge about component interactions (biofilters, mechanical filters, energy flows).
• Interaction of pathogens and benign microbes in biofilters is very poorly understood.
• Biofilms, biomats etc need more study.
• Scale up problems are common: thorough testing is still necessary.
• Modified processes may be required when using new feeds.
• Accumulation of bi-products in the systems are poorly understood.
• There is a need for predictive modeling to assess multifactor interactions in recirculation system design and testing.

The design of feeds for recycling systems will: need to weigh conversion efficiency versus water treatment efficiency. Currently, feeds can be designed to facilitate the separation of faeces from the water and for reduction of nutrient leaching.

Intensification can cause stress by disrupting fish social structures – but this varies with species – some do better at high stock densities, and we need to know more about such behavioural characteristics. Fish may require pre-adaptation to the recirculation environment. Recirculation techniques can also be highly species-specific. Species that are currently difficult to culture can be selected to perform better in recirculation systems. As expected, strains that have been cultured and adapted to recirculation systems seem to perform best.

Welfare concerns as well as the desire for improved productivity will compel us to design systems to suit the needs of the cultured animal.

Water is not always the limiting factor that makes recirculation an attractive option– in some cases it may be energy conservation such as heated hatchery and/or grow-out systems.

New approaches

An important future environment for aquaculture expansion is the sea, particularly offshore waters. Currently coastal waters, bays and inlets etc. are utilized but the cost of open water development is currently prohibitive in most instances.

As we enter the new millennium, it is noticeable that the rate of increase in global aquaculture production is slowing. If this is due to production limitations, it suggests we are not using current technologies well, or alternatively those future increments will be more expensive to achieve. We therefore need fundamental innovations in aquaculture technology and it would also be useful to determine the potential performance of the available species, to help us optimise culture conditions.

The slowing of growth of aquaculture production is largely due to the effect of major current producers, as a result of saturation, problems with disease and environmental limitations. We should also take account of huge longer-term potential in South America and Africa, for which suitable technologies might already be available but have yet to be effectively transferred in a manner suitable to the prevailing local conditions.

Fish cage systems

The production of fish from cages is increasing globally. The technologies are now well developed in Europe, parts of South America (Chile in particular) and China. In SE Asia, cage farming of fish is advancing rapidly, in a wide range of species; the main limitations being the availability and high cost of feeds and shortage of seed. There is already considerable transboundary movement of fish seed and fingerlings in Asia, mainly for live fish markets in Hong Kong and China. Little is known of environmental impacts, although this trade is known to result in some destructive fishing techniques for fish fingerlings.

Each country has its own species, markets and issues that need to be addressed in the development of cage culture, but future expansion of this farming system is expected.

Inshore-nearshore cage farms:

Environmental impact minimization, or even positive impacts, can be achieved with inshore and nearshore cage farms. For example, combinations of fish cages with seaweed and shellfish culture can reduce nutrient and organic loading, combining cages and artificial reefs can contribute to stock enhancement and could have a long term potential for culture based fisheries.

There are a number of other technical issues that include:

• Making better nets, (stronger, less prone to attack by predators, and coping with fouling (while reducing use of antifouling paints);
• New designs, in particular deeper, larger and submersible cages;
• Increasing scale requires new levels of risk management;
• Equipment for sorting, handling, counting, biomass estimates.

Environmental management issues will be particularly important for the future development of cage culture. The issues to be addressed include:

• Better knowledge about mortality and real number of fish in cages, better feeding regimes, with less waste of feed;
• Thorough study of material and energy flows through cage systems;

• Modeling of the environmental impacts (not only benthic deposition, but also nutrient release and dispersal);
• Better knowledge about recovery processes, so as to estimate fallowing time;
• Site rotation: better equipment for simpler mooring;
• Models are lacking that relate to remote zones and interactions between nearby farms.
• Improved management of coastal zones, access rights and ownership are required in many countries that have the potential for expansion of coastal aquaculture.

Offshore cage farming - its technology needs and future

Open sea farming provides better exchange and dispersion of wastes, can be designed to be technically safe, but needs better surveillance techniques, and remote control of feeding. Production costs are still too high and most current examples are still prototypes. Furthermore, performance of fish may be different offshore than inshore – not enough is known on this issue.

Infrastructure needs are likely to be different from near-shore cage systems. Systems may be offshore for a long time without being brought inshore for service - net repair and maintenance will be special issues. Different support systems (platforms) may be needed offshore - space for sorting, harvesting, handling, checking, treating.

Options for this technology in the short term will revolve around the high value species.

Infrastructure and support technology

Infrastructure and support technology issues relate mainly to environmental assessment and planning and include:
1. Computerization of aquaculture

• Financial control
• Decision support systems for planning
• Better farm management software
• Better online monitoring equipment and reliable calibration and self-diagnosis (for biomass, environmental parameters).

2. Improved zoning and regulation and environmental management

• Incorporating GIS in System management
• Better methodologies for Impact assessment - e.g. carrying and holding capacity models.
• Mass application of vaccines and parasite treatments within production areas.

Standards for materials

Other food sectors have strict regulations on the materials used: these are largely lacking for aquaculture. For example, plastics contain low molecular weight components, which may be a source of contamination. These include plasticizers, stabilizers, lubricants, coloring material, UV absorbers, antistatics, and flame retardants. Here there may be a need for standards for materials in recycling systems because those going into solution may contaminate the system and the product.

The quality and standards for feeds in aquaculture whilst relatively rigorous in some countries will need to become more rigorous in many countries in order to respond to export and market requirements.

Future potential species for aquaculture

When aquaculture is compared with the livestock sector it may appear that we may be trying to culture too many species. On the one hand it is the sheer diversity of species that allows us to exploit many varied environments and niches to enhance aquaculture production (also considering that livestock are all mammals). On the other, this diversity also makes it problematic to standardize and generalize in the same way that we now control the limited options within the livestock sector.

Species choices need to be made with great care, taking into account market demand, availability of seed and of culture technologies, and the potential environmental constraints. Some of these issues include:

• Development of indigenous species rather than exotics;
• Filling market niches in particular areas (for example cod, haddock and halibut in cold waters);
• Diversification is still a priority for Mediterranean aquaculture, where several
faster-growing species can occupy the same infrastructure, and their life cycles have been closed.

• Pelagic species may become more significant if economic culture systems can be developed.
• Air-breathing fish could fill specific situations of low technology and poor water quality.
• Improved seed supply (both in terms of quantity, quantity and distribution). More microalgal species are required for hatchery feeds and for production of fine chemicals.
• Similar comments apply in tropical and subtropical areas, with alternative shrimp and other crustacean species, indigenous fishes rather than the Chinese and Indian cyprinids, freshwater mussels, shrimps and snails being mentioned.

There is a priority to close life cycles of species currently being grown out in aquaculture.

New Products

The economic efficiency of aquaculture can be greatly improved by the discovery of new products, not only for consumption but also for other uses, resulting in fuller use of currently cultured species. An example of using fish as bio-reactor or as tool in developing pharmaceuticals, is the possible use of salmon in finding a cure for osteoporosis.

Education and training

Education and training has to be given more attention in the new millennium. The quality of training should be assured through industry-based competency standards, the accreditation of courses and frequent re-training of the training providers themselves.

New techniques for the effective dissemination of information to others who influence the progress of aquaculture, such as policy makers, public servants, investors, engineers, journalists and the general public is urgently required.

Recommendations

The factors, which drive aquaculture development, cover a spectrum from the needs of people (the provision of local employment, food security and the alleviation of poverty) to the needs of industries (with particular emphasis on profits, productivity and consistent-quality products).

The requirements for sustainable aquaculture development will include both technological and people based approaches From this range of choices, the design and selection of appropriate culture systems can be made, which most effectively meets their needs and best fits the opportunities and constraints of the local environment.

Although such techniques exist, their widespread dissemination requires effective communication networks, reliable data on the merits and drawbacks of the various approaches, and help in the decision-making process through which people design their production systems.

We predict that access to supplies of suitable water (coastal, estuarine and particularly freshwater) will become increasingly problematic and will be the source of widespread competition. Aquaculture will have to adapt to this. Therefore, we must adopt or develop approaches which:

• Use water more efficiently;
• Promote further integration of aquatic production with agriculture (e.g. crops and livestock), particularly in areas where such approaches are not common;
• Link with, share with or complement other water resource users; and
• Use water for which there is less competition due to its reduced suitability for drinking, irrigation, agriculture etc..

High-technology systems are often proposed to achieve the more efficient use of water (e.g. recirculation), or to avoid competition for water (e.g. offshore/oceanic farming). Since there is a relatively high risk of failure of such systems, we recommend:

• Pilot-scale and full-scale testing, in real settings, for newer culture systems before their adoption by users;
• Standard criteria for materials, procedures and safety margins applied in newer culture systems;
• Codes of practice for specific culture systems as used in specific applications.

Current recirculation systems are expensive and limited in their applications for most species. The functional interactions of their components are not well understood, and this makes it difficult to optimise systems for specific applications (e.g. quarantine, hatchery, grow-out).

There is an increasing need for environmental and system control as a result of intensification. We therefore recommend:

• The further development of cost-effective recirculation systems for other species;
• The further development of recirculation techniques for green-water or turbid water as well as clear-water systems;
• Research and development on reliable monitoring and management tools that go beyond current limited water quality criteria (e.g. biomass, mortality, growth, behaviour, critical events);

The composition of discharged water is an important factor in environmental sustainability. We recommend that research continues strongly in the areas of:

• Biological treatment of waste waters, leading to improved design, reliability and cost-effectiveness of such systems, and methods for the disposal of sludge;
• The design of feeds which minimise the wastage and excretion of nutrients, and facilitate more efficient waste treatment (e.g. faeces separation);
• Use of effluents, including sediments, in other agricultural processes.

Both the need for efficient use of resources (especially water), and pressures exerted by the community, will require that farming systems are designed to meet the needs of the farmed animal. We therefore recommend more research on:

• The behavioural responses of cultured animals to the culture environment, leading to system optimisation, and in particular to achieve species compatibility in polyculture systems;
• The minimisation of stress and other adverse physiological responses to the culture environment and the harvesting process;
• Domestication and selection of animals for improved performance in culture.

The ability of aquaculturists to meet their diverse needs, in the various environments used, depends on the diversity and adaptability of their system options.

One critical option is the cultured species. We therefore recommend that research on new species continues in a judicious and selective fashion, particularly in the following areas:

• Development of suitable indigenous species rather than exotics;
• Additional species in geographical regions where major market niches are not yet satisfied, (for example cold water regions and the Mediterranean);
• Closure of life cycle of species already being grown out on a substantial scale;
• Air-breathing fish species suitable for culture in systems with unsophisticated technology and poor water quality;
• A wider range of species, including molluscs and crustaceans, for freshwater culture.

Aquaculture can be made more economically efficient through the development of additional products from the species grown. We recommend more research and development of fine chemical and pharmaceutical products from cultured organisms, including fish and invertebrates as well as algae and microorganisms.

Whilst further exploratory research must be done to achieve a quantum leap in aquaculture productivity, the effective dissemination of this knowledge is a key to future growth. Aquaculture of all types requires high levels of skill and professionalism, whether it is highly integrated with other users, or highly intensive and industrial, and generally because of its complex interactions with the local environment. We therefore recommend:

• That all relevant agencies strongly encourage programs for the training of aquaculture producers and service providers;
• That the quality of training be assured through industry-based competency standards, the accreditation of courses and frequent re-training of the training providers themselves;
• Effective dissemination of information to others who influence the progress of aquaculture, such as policy makers, public servants, investors, engineers, journalists and the general public.