Ouk Vibol
Department of Fisheries, Cambodia 186, Norodom Bld, Phnom Penh, Cambodia
and
Niklas Mattson
Mekong River Commission, Box 7035, Vientiane, Lao PDR
ABSTRACT
The Mekong River is one of the world's largest rivers, with possibly the largest inland fishery. Aquaculture contributes around 10% of the total fish production in the four countries of the Mekong River basin. Exotic species dominate in aquaculture, especially the Indian and Chinese carps, tilapia and the African catfish. At present, exotic species can be found in natural water bodies, including Tonle Sap Great Lake and the Mekong River. These species have been intentionally and accidentally released, and may cause genetic pollution, feeding competition and introduction of diseases. The main cause of inbreeding is lack of broodstock, especially in small scale hatcheries (in Cambodia), where space constraints may limit the number of broodstock that can be kept. The introduction of indigenous species in aquaculture in some riparian countries is constrained by lack of domesticated broodstock, risks of genetic pollution caused by release or escape of domesticated fish, disease dissemination, high production cost and lack of human resource with expertise on research into breeding and raising technologies. Aquaculture of Indigenous Mekong Fish Species (AIMS) Component has been created in order to carry out research on economically feasible and attractive aquaculture systems using indigenous Mekong fish species that may complement or replace the use of exotic species for culture purpose in the Mekong basin. Networking is actively supported in order to facilitate exchange of ideas and experiences relating to indigenous Mekong fish species. A total of 19 indigenous Mekong fish species has been selected and 11 research stations from four countries have been assigned by governments to conduct the research. One protocol of AIMS will be to avoid transfer of live aquatic animals between countries. The component is collaborating with other agencies (including AIT, FAO, and NACA), in order to share experience and provide training to AIMS staff.
At more than 4 400 kilometers in length, the Mekong is one of the world's largest rivers. The total basin population is approximately 73 million (MRC, 2000), and the Lower Mekong Basin is home to some 60 million people, three-quarters of whom earn their living from agriculture and fishing, which account for 50 percent of the Lower Basin's GDP. Typically, land holdings are 1-2 ha. In Cambodia, Lao PDR and Viet Nam the estimated annual per capita income among subsistence farmers is US$ 150 - 200 (higher in Thailand).
Fish production in the Mekong Basin is quite substantial, with a total production of not less than 1 000 000 tons. Much of this production comes from family-based subsistence fisheries and about 10 percent is contributed by aquaculture.
The aquatic resources of the Mekong Basin represent an enormous biodiversity with more than 1 200 fish species as well as numerous other aquatic animals and plants. In recent years, some species are increasingly rare due to impacts on the physical environment as well as overexploitation, including the use of destructive fishing techniques.
Capture fisheries provide most of the fish required in the Mekong region, but in recent years aquaculture is an increasingly important contributor to fish production in the region. At present, exotic species dominate the aquaculture industry; especially tilapia and Chinese carps, including silver carp. Indigenous species that are being cultured include silver barb (Barbodes gonionotus), Clarias batrachus, Pangasius hypophthalmus and Channa micropeltes (Nandeesha, 1994).
The widely cultured, well-known exotics have been the primary target for past aquaculture development initiatives. Over a short time perspective, these species provided better chances of increasing and improving aquaculture, and were therefore the organisms of choice. Coupled with lack of attention to development of aquaculture techniques for indigenous species, this resulted in the dominance of exotics. The introduction of exotic species, intentionally or accidentally, to a system as diverse as the Mekong Basin, can be considered undesirable, when there is so much local potential that could be developed. The impact of introductions of exotic fish species is unpredictable, and has resulted in negative impacts in some cases.
The MRC Programme for Fisheries Management and Development Cooperation has been created in order to ensure the coordinated and sustainable management, use and development of the economic and nutritional potential of the inland living aquatic resources in the Mekong River Basin. The Component of Aquaculture of Indigenous Mekong Fish Species (AIMS) is a part of the MRC Programme for Fisheries Management, with the goal to safeguard the indigenous fish resources quantitatively, as well as in terms of biodiversity, from negative side effects of continued spreading of exotic fish species in the aquatic environment.
2.1. Genetic effect that occurs in using exotic species (effect on local stock by intentional or accidental release of exotic species)
Presently, several exotic species are already established in the basin, but the impacts of exotic fish farms (carp farms) on the environment are poorly documented.
At present, inland aquaculture and enhanced reservoir fisheries in the Mekong basin are almost exclusively based on exotic species, especially Indian and Chinese carps, tilapia and African catfish. Due to the annual flooding, particularly in Cambodia, some fish invariably escape from the fish ponds into the river and lakes. The problem of fish escape is also great in cage and enclosure culture system. Fish held in cages and pens frequently escape through holes in netting or mesh caused by predators, floating objects or rough weather. In addition to the fish released by accident, in some regions exotic species are intentionally released in rivers or lakes. These releases may cause changes in predation, competition for food, introduction of diseases, genetic pollution and co-introduction of nuisance species.
Beside the potential environmental problems caused by exotic species, exotic fish species (e.g. tilapia) are not very easy to market, and generally fetch a low price.
2.2. Opportunities and constraints for development of aquaculture systems based on indigenous species
A change in the development trend away from exotic species and towards a more environmentally friendly development of aquaculture is preconditioned by the development of economically feasible new techniques. Given such techniques, indigenous fish may complement or replace the culture of exotic fish species.
FAO (1997, p.21) emphasises that aquaculture stocks or stocks for culture-based fisheries can be managed within the culture facility:
1. to avoid inbreeding,
2. maintain stock integrity by hybridizing different stocks, strains, or species,
3. by minimizing transfer of genetically different stocks, and
4. by periodic assessment of their genetic diversity (i.e. laboratory genetic analysis).
2.2.1 Introduction and selection of indigenous fish species
Indigenous species are often promoted as alternatives to introduction of exotic species for aquaculture development. They may be preferred locally, may have less chance of introducing disease, may grow better under local conditions, may contribute to preservation of biodiversity, and help maintain integrity of aquatic communities and ecosystems by appropriate management (FAO, 1997). Among the more than 1 200 fish species in the Mekong Basin, it may not be difficult to select and develop some species for aquaculture development. Species should be selected based on the performance of the fish in culture, the desired breeding programme, the genetic profile of the broodstock, and last but not least economic and environmental considerations.
2.2.2 Breeding and genetic improvement
The development of aquaculture of indigenous species may aim to conserve genetic resources. However, introduction of domesticated indigenous stocks also poses a potential threat to biodiversity. The FAO Technical Guidelines for Responsible Fisheries, Aquaculture Development (FAO 1997, p.22) state the following on the use of indigenous (native) species:
"Native species are often promoted as alternative to introducing exotic species for aquaculture development... However, native species taken from the wild and domesticated or subjected to other genetic modifications may also pose a risk to the remaining wild stocks, both from genetic and disease standpoints."
Brood fish collected from the wild need to be domesticated in order to tolerate the hatchery conditions. The domestication process imposes specific selection pressures, which are different from those in the wild, and the genetic profile of the cultured organisms will invariably change. The culture of non-reproductive fish (e.g. sterile, triploid or mono-sex populations) will reduce the chance of released or escaped organisms breeding in the wild.
2.2.3 Inbreeding and genetic drift
Decreasing hatchability, fertility and survival, and increasing prevalence of deformities and diseases, may be signs of inbreeding and loss of genetic diversity. Many hatcheries are small, and consequently only capable of maintaining limited numbers of broodstock, which can rapidly give rise to inbreeding. This situation occurs in the Mekong Basin, e.g. in Cambodia (Funge-Smith, 2001). In general, small-scale farms may have only one or two ponds for maintaining or conditioning broodstock. One or two pairs of broodstock are bred and then kept for the next breeding season. The larger fingerlings from those pairs are selected as new brood fish and kept together with the parents. This may rapidly lead to inbreeding.
Large state hatcheries could provide a pivotal role in maintenance of genetic quality of broodstock, due to their ability to maintain large stocks and control breeding. Currently, controlled breeding is rarely practiced and management of fish is limited to selection and breeding of fast growing fish. This is principally due to lack of awareness of how to manage stocks and the inherent risks of inbreeding.
Inbreeding may be reduced or prevented by improved broodstock management, including periodic introduction of new broodstock from the wild. Funge-Smith (2001) mentions several methods for reducing the risk of inbreeding:
- Selective stripping of eggs and milt so that the breeding of individuals can be controlled. This would usually be accompanied by tagging of the fish so that records of breeding could be kept.
- Broodstock pairs are used only once and the fingerlings from that batch form a percentage of new broodstock.
- Stretching of generations of broodstock. If the same broodstock are spawned over two years instead of one, then a smaller effective breeding number can be used.
There is considerable expertise on the breeding of indigenous fish species in some of the riparian countries. The selection of species for artificial breeding experiments has been determined by various factors such as availability of breeders, by the wish to restock newly formed reservoirs or water bodies cut off from natural recruitment by dams, or by spot-wise checking of the suitability of certain species for aquaculture.
Technical problems may be encountered in finding good quality broodstock in nature, and in obtaining broodstock maturity in time. Broodstock caught in the wild may carry diseases.
Compared to the established exotic species, breeding of some indigenous Mekong fish may not be profitable. For example, to rear Pangasius hypophthalmus to reach maturity takes at least 4-5 years and the maintenance costs of the broodstock alone represent approximately 50% of the production cost of the fingerlings sold (Funge-Smith, 2001).
Developing indigenous Mekong fish species for aquaculture is relatively much more demanding, since a lot of basic research needs to be carried out, and training is required for government officers taking part in this effort.
As part of an attempt to reduce the spread/impact of the aquaculture of exotic fish in the Mekong basin, the immediate objective of the component of Aquaculture of Indigenous Mekong Fish Species is:
"Economically feasible aquaculture systems developed using indigenous Mekong fish species, which may complement or replace the exotic species for culture purpose in the Mekong".
The Component Description refers to the establishment of a Network in order to exchange ideas and experiences relating to indigenous Mekong species. There are networking needs at different levels, from farmer level, via component level (research institutes) to the wider public, including development/research organizations elsewhere. The AIMS component also collaborates with NACA on this, and the MRC web site.
A total of 19 priority species have been promoted for further research by AIMS (2000), including Anabas testudineus, Barbodes altus, Barbodes gonionotus, Cirrhinus microlepis, Cirrhinus molitorella, Clarias macrocephalus, Henicorhynchus siamensis, Leptobarbus hoeveni, Macrobrachium lanchesteri, Morulius chrysophekadion, Mystus wyckioides, Notopterus notopterus, Osphronemus gourami, Osteochilus melanopleurus, Pangasius hypophthalmus, Pangasius larnaudiei, Pangasius bocourti, Puntioplites falcifer and Trichogaster pectoralis. Some fish species overlap between countries, and Cambodia, Lao PDR, Thailand and Vietnam have agreed to carry out studies on 6, 6, 7, and 6 species, respectively. The criteria used for selecting the fish species included potential for low input aquaculture, market demand, potential for farmer-based (simple) hatchery production, etc. A total of 11 research stations have been selected for collaboration with the AIMS component, with two in Cambodia, three in Lao PDR, five in Thailand and one in Vietnam.
In all four countries, broodstock have been captured and/or selected from exiting stocks. In order to avoid inbreeding, at least 100 fish of each species have been collected. The brood fish that has been collected from the wild have to be acclimated to the captive pond environment. Simple breeding and hatching technologies, larvae culture, water control and management will be applied in order to evaluate the economy of the culture systems.
Research into non-reproductive fish such as sterile, triploid or mono-sex populations of organisms will not be priority. AIMS is not in a position to conduct extensive genetic examination of stocks, but might be able to facilitate and partly fund such research through its four-country network, should such an opportunity arise. AIMS may also facilitate awareness raising within the four countries by providing some simplified guidelines regarding genetic management of hatchery broodstock. AIMS will not support the uncritical movement of live fish between countries or sub-catchments.
The development of farming systems is also a goal of AIMS. Species successfully bred and raised as part of on-station research and with good economic potential will be subjected to full-scale tests on-station and on-farm in cooperation with the national fisheries extension services, NGOs, international organizations involved in fish culture development and with selected farmers. Promising technologies and extension approaches and species will be extended to other areas, and gradually replace the exotic species. The Component has identified the following areas for short-course training, which to some extent may differ between countries:
- Broodstock management, including genetic considerations and movement of live fish
- Species identification
- Feed and feeding
- Participatory monitoring and evaluation approaches
- Health management/disease prevention
- Project management, monitoring and reporting
- Introduction to experimental design and analysis
- Information management and networking.
The training will be carried out at local, national and regional level, in collaboration with local and regional training institutions as well as universities.
Several exotic fish species are already established in the basin, although so far there are few reports of problems related to these species.
Low numbers of broodstock in many hatcheries cause inbreeding.
Responsible development of indigenous species: aquaculture can reduce or minimize the risks associated with exotic species.
Development of indigenous species: aquaculture is faced with some constraints:
- in relation to availability of domesticated broodstock,
- genetic side effects due to domestication,
- human resources in terms of expertise in breeding and raising technologies.
AIMS's goal is to develop a total of 5-8 indigenous species, which are expected to provide profitable alternatives to culture of exotics.
AIMS has a strong environmental focus, and will pay special attention to:
- genetics and broodstock management
- transboundary movement of live fish
- environmental management of indigenous fish farming systems
- economics of indigenous fish aquaculture and genetic diversity.
References
AIMS, 2000. Inception report. MRC, Phnom Penh, Cambodia.
FAO, 1997. FAO Technical Guidelines for Responsible Fisheries, Aquaculture Development (No. 5). FAO, Rome. 40p.
Funge-Smith, S., 2001. Activities planning and hatchery renovation, Cambodia. Consultants report for MRC/AIMS. MRC, Phnom Penh, Cambodia.MRC, 2000. Mekong River Commission for sustainable development. Annual Report. MRC, Phnom Penh, Cambodia.
Nandeesha, M. C., 1994. Fishes of the Mekong River - conservation and need for aquaculture. Reported from NACA, ICLARM, Q. 17(4): 17-18.
