Appendices (continued)

Appendix 4: Extended Abstracts

Nine different river systems are identified that drain the interior of Southern Africa. These river systems are presented in table 1 and consist of the following:

• The Congo-Zaire System. This system drains part of Angola, Burundi, Cameroon, Central African republic, Congo, Rwanda, Tanzania, Zaire and Zambia. It includes the large lakes Tanganyika, Kivu, Mweru and the Luapula floodplain.

• The Nile system, drains parts of Kenya, Tanzania, Uganda, Burundi, and Rwanda, and includes the lakes Victoria, Cohoha, Rweru, Kyoga, Edward, and Albert.

• The East Coast River Systems. The rivers in this system, the Pangani, Wami, Ruvu, Great Ruaha, Rufiji and Ruvuma, drain Tanzania and part of Mozambique and flow into the Indian Ocean.

• The Zambezi River System drain parts of Angola, Zambia, Zimbabwe, Malawi, and Mozambique. It includes Lake Malawi/Naissa and the man made lakes Kariba, Cahora Bassa, Itezhi tezhi and Kafue.

• The Okavango River System drain parts of Namibia, Angola and Botswana. It does not drain into an ocean but drains into the Okavango delta. At times of high water the Okavango Delta overflows into the Chobe river and connects to the Zambezi River System.

• The Cunene River System drains part of Namibia and Angola and discharges into the Atlantic Ocean.

• The Limpopo River System discharges water from Botswana, Zimbabwe, Mozambique and South Africa into the Indian Ocean.

• The Orange-Vaal River System. drains parts of Lesotho, South Africa, Botswana and Namibia. It discharges into the South Atlantic ocean.

• The Cape System drains the southern parts of Africa, including parts of Mozambique, South Africa and the whole of Swaziland.

Table 1: Number of Fish Species in various river systems in Southern Africa.

From the perspective of fish species distribution these river systems can be subdivided into various other systems. Not every fish species found in a certain system is distributed over the whole system. Physical barriers, like water falls and dams, prevent this, but also temperatures, currents and other chemical/physical characteristics of the river influence the species composition. Several rivers, e.g., the middle and lower Zambezi and Pungwe and Save rivers have a reduced fauna. This is typical for east coast rivers, due to the fact that the river bed is essentially rocky or sandy, providing little cover for small fish species. Larger lakes provide a different environment for fish. This has been evident with the construction of Lake Kariba on the Zambezi system. Fish species that were found in the upper Zambezi but absent form the middle Zambezi were established there after the construction of the dam.

The number of fish species decreases from north to south and increases in systems that include large natural lakes (table 1).

Introduction

Fish speciation is determined by the aquatic environment, including water temperature, the physical characteristics of the water, water quality, food sources etc. In Southern Africa the Zambezi River System holds around 178 fish species. South of this system the number of species decreases gradually. North of the Zambezi System the large rivers hold many more species.

Species for aquaculture and fisheries

Around the Cape the rivers only hold a few indigenous fish species. The limited variety of the indigenous species there and especially the sparse knowledge about them prompted the introduction of a variety of alien fish species to increase the fish production from the rivers and dams.

Alien species important for fisheries are the common carp (Cyprinus carpio), rainbow and brown trout (Onchorhynchus mykiss, Salmo trutta), and largemouth bass (Micropterus salmoides). The kapenta (Limnothrisaa miodon), and green headed tilapia (Oreochromis macrochir) have been translocated between countries in the region, while the Nile tilapia (Oreochromis niloticus) and Nile perch (Lates niloticus) are translocated to Tanzania from waters in that region.

Worldwide, most aquatic introductions have been made for the purpose of aquaculture. This makes sense from the point of view of the fish farmer, who wants to maximize his returns. Species with well known and proven aquaculture performance and known breeding and growing techniques are obviously preferred by fish farmers. Species introduced for aquaculture are O. macrochir (in South Africa and Tanzania), O. niloticus (in Zimbabwe, Zambia, Tanzania, and Mozambique), C. carpio (in South Africa Zambia, Tanzania, Malawi, Swaziland, Mozambique), Ctenopharingodon idella (in South Africa, Zimbabwe, Zambia and Mozambique), Hypophalmichthys molitrix (in South Africa, Zambia, Zimbabwe and Mozambique) and O. mykiss (in South Africa, Zimbabwe, Malawi). Besides these fish species three exotic crayfish species are used for aquaculture in Zambia.

The decision about which species to use depends mainly on the scale of the aquaculture enterprise and the source of information and fish. Small-scale rural fish farmers mostly use species that are promoted by the aquaculture authorities, because they lack the knowledge about, or have no access to, other species. Large-scale farmers often have access to information about the culture of exotic species, and when there is a possibility to obtain them they tend to use them.

Research on Candidate Species for Culture

The selection of candidate species for culture is based on many factors, including production potential in a given environment and consumer acceptance. Research on reproductive biology, feeding habits and growth performance under culture conditions is needed to develop feasible culture methods. Research in Southern Africa has in the past mainly focused on the adaptation of the culture of exotic species to local conditions, but has since gradually moved towards the development of culture methods for indigenous species.

Discussion

Southern Africa has a wide variety of indigenous fish species and several of these species are being studied and tried for small reservoir fisheries and aquaculture production. To yield useable and lasting results this research needs to be well directed, long term, and linked to extension systems that deliver practical techniques to farmers.

International agreements

The international Convention on Biodiversity is probably the most relevant piece of international legislation. The Convention recognizes the value of natural and domesticated biological diversity and acknowledges the sovereignity of countries over their resources. The Convention addresses the issue of the introduction and transfer of species, and provides for cooperation between states. Malawi and Zambia are however the only two SADC countries who ratified the Convention.

Regional agreements

SADC was set up by treaty in 1980. One of the main objectives of the treaty was to ensure that development does not impair the diversity and richness of the region's natural resource base and the environment.

The SADC Policy mentions that “Priority problems in the region include .... the extinction of indigenous species and loss of support systems of fisheries and wildlife”. However, there appears to be no clearly stated policy on the introduction and transfer of aquatic species within the region.

Bilateral agreements

Cooperation mechanisms and/or joint commissions exist for most of the shared lakes in the region. However, there are no legally binding agreements in force despite there being a commonly recognized need for such agreements for Lake Kariba, Lake Malawi/Niassa and the Zambezi and Limpopo rivers.

National legislation

Currently, of most countries in the SADC region, legislation exists at the national level governing the import, export and transfer of species. Most countries also have legislation which does not prohibit transfers of fish but states that they should only be allowed once a permit has been granted.

Other legislation

In addition to fisheries legislation there may be other legislation relevant to the import or export of fish. For example, in Lesotho the Minister may ban the import and export of goods in the public interest.

Administration and enforcement of the law

At the national level, within the SADC region, the legal framework is in place to control the introduction and transfer of fish. Neither the practice of authorizing permits to import or transfer fish, nor the criteria used to authorize such activities is well documented so it is difficult to asses to what extent introduction and transfer of fish is controlled. There are also numerous difficulties associated with enforcing legislation in countries whose fisheries and other government department often lack the resources to carry out these duties. In addition there are problems of collaboration between government departments, especially with regard to the import and export of live aquatic organisms.

Conclusions

A review of the existing legislation indicates that at the national level in most SADC countries there is sufficient enabling legislation to regulate and control the import and transfer of fish. However, at the regional level and especially with regard to shared river systems including lakes, legislation is inadequate.

In conclusion, there is clearly a need for greater cooperation between SADC states on the legal issues pertaining to the introduction of aquatic species in river systems with cross-national boundaries. However, laws are only useful if they can be effectively enforced, which within the SADC region, will remain the more immediate problem.

Introduction

Cyprinids are amongst the most important species in aquaculture. The various carps are well-known to aquaculturists and are used extensively for aquaculture. Some of them have been introduced into countries all over the world where they contribute to fish productivity in various ways.

Africa has a large and diverse cyprinid fauna and they contribute significantly to the fish catches from its rivers and smaller lakes. Some of them would appear suitable candidates for aquaculture. In spite of this, none of them seem to have been used for this purpose.

The advantages of cyprinids for aquaculture are their high fecundity and the absence of uncontrolled and precocious spawning in ponds.

Suitable species in Southern Africa

There are a number of Barbus and Labeo species that grow to a large size and might therefore have some value in aquaculture. Some of them are valuable for angling purposes and some are endangered. Because the Labeo's are predominantly rheophilic and andromous their numbers are affected by changes in river flow patterns, caused by drought and/or damming, degradation of riverine habitats by siltation or pollution, and by intensive fishing during their breeding migrations.

In time, it may become necessary to consider rearing these fish in hatcheries in order to restock rivers and augment the remaining natural populations.

Are cyprinids any good as pond fish?

Very little is known about the biology of African cyprinids. Artificial spawning will be necessary, as these techniques are well known of other cyprinids, they can easily be adapted to the local species.

The growth rates are unknown and little work has been done to determine the growth rate under pond conditions. The work that has been done suggest that growth in ponds is poorer than the growth of common carp and tilapias.

Where to go from here?

At present there seems to be little prospect that Southern African cyprinids will be able to make a significant contribution to aquaculture. The first priority will be to determine the growth rates of the various species, after that the performance under different culture systems has to be established, and finally investigations into large-scale hatchery propagation should be made.

Conclusions

The hope that Southern African cyprinids can be extensively propagated and used in aquaculture seems unlikely to be fulfilled in the near future. This requires a program of basic biological research.

Introduction

Fish is farmed for various purposes, but it is farming of fish for human consumption which is of prime importance. An overview is given of the potential of species in aquaculture.

Aquaculture potential

The aquaculture potential of fish species should be divided into three categories:

• The culture and large-scale production of fish to be consumed as protein source. In South Africa the sharptooth catfish, Clarias gariepinus, is a good example of indigenous species for which culture techniques were successfully developed. Labeo sp., as well as Schilbe intermedius offer potential for production from large dams, but more research into the maximum yields and large-scale production is needed before final decisions can be taken.

• The importation of ornamental fish in South Africa is between 8 and 12 million rand per year. Several indigenous species offer potential as ornamental fish, the culture of these potential species is in different stages of development. If the culture of aquarium fish can be developed and the ornamental fish industry can be changed to an exporting instead of an importing industry, it will have considerable financial implications for South Africa.

• Four Barbus sp. and the tigerfish, Hydrocinus vittatus, have recreational potential. Research is carried out to develop suitable techniques for mass production of these species. The aim is reseeding these species into natural waters where changing environmental conditions caused a decrease in population numbers.

Conclusions

It is evident that there are a number of cyprinids and other finfish species which show potential for exploitation in aquaculture. This includes harvesting in large impoundments, controlled culture for human consumption, aquarium application and recreational fishing. A great research effort has to be initiated to supply the necessary information for the establishment of controlled culture techniques.

Farming crustaceans and molluscs in Southern Africa is not well developed, but is likely to intensify in coming years. The pressure will increase to introduce candidate species to satisfy specific culinary demands or improve bulk yields and efficiencies.

Several freshwater crustacean species have already been introduced in Southern Africa, often without the knowledge and permission of the authorities. Introduced freshwater crayfishes constitute a totally new element of African and local fauna, as such species were not present in the continent originally. In comparison, Australia has almost 100 species of fresh water crayfish, North America over 300 and Europe five. Introduced species form North America and Australia could thus be considered as occupying non-utilized ecological niches in Africa. However, the introduced species should not be considered only as a valuable addition, because they often cause ecological imbalances with rapid and dramatic consequences.

Possible solutions to avoid such consequences in farming crustaceans and mollucs are:

• Countries should include a crustacean and mollusc species policy as part of the national fisheries policy and national conservation policy. There is a need for better harmonization of conservation and fisheries policies in this respect between countries.

• Surveys and monitoring of the conditions of the present stocks in relation to alien species or planned stocking of alien species.

• Development of culture methods for native species and restocking these species in waters where they have disappeared.

• Designation of exclusive areas for already introduced alien species.

• More research to formulate safe farming and better management strategies for crustaceans and molluscs.

Features to be considered when selecting or rejecting fish for farming

Usually fish species for fish farming are selected on the basis of:

• Yield achieved in ponds.
• Growth rate, which is defined as the increase of individual weight of the fish over time.
• Food conversion rate, the ratio of food supplied to the fish to the increase of weight of the fish.
• Ease of breeding.
• High fecundity.
• Early maturation, to ensure that fish does not start breeding before it reaches market size, but early enough so as to prevent keeping broodstock for years.
• Resistance to diseases.
• Adaptability to a wide range of environmental parameters.
• Hardiness to handling.
• Market value.

What is the best species for fish farming

No species will meet all the set criteria and therefore the selection criteria have to be prioritized. In order to prioritize the criteria a number of assumptions have to be made with respect to the objectives of the fish farmers, the conditions under which the fish will be cultured and the needs of the farmers.

The criteria

Complaints on the performance of the species used for fish farming in Malawi are common. It is said that the fish grow slowly, breed precociously, or that fingerling production is not providing enough fingerlings and that overall production is low.

If the performance of the species used in Malawi is poor, the first question to ask is why they do not perform as required. Programs of selective breeding and intraspecific hybridization have to be set up. For these programs specific breeding goals have to be set. If selective breeding cannot achieve the set goals, then the choice of species needs to be reviewed and new strategies for supplying the farmers with suitable species devised. This could include introduction of exotic species, but only when the classical improvement programs have failed.

Introduction

Domesticated stocks have been subjected to processes of evolution as humans impose selection pressures on crops and animals in order to adapt to the environmental conditions and human preferences. Aquaculture is relatively young, and most cultured fish species are still close to their wild counterparts. Genetic material is still collected from the wild. Exceptions to this are the common carp (Cyprinus carpio) and the domesticated variety of the crucain carp, the goldfish (Carassius auratus).

Introductions of exotic species can only be justified when the inadequacy of the native species has been demonstrated. Most Southern African countries have rich genetic resources of fishes in the natural waters. The major task of aquaculture scientists and managers is to assess the culture potential of these species.

Genetic characterization of indigenous species

Genetic characterization is an essential component of the screening package for the candidate indigenous species for aquaculture in order to determine the amount of genetic variation that exists and identify the various strains of a particular species. Genetic variation shows the level of heterozygosity which is an important indicator of the potential response to selection.

Most of the domestication programs for fish in Africa have been constrained by the fact that they work on species that have not been properly identified. Lack of documentation on the available genetic material is caused by a lack of trained personnel to identify the species and also a lack of facilities.

Population structure

Information on population structure of a species is important for determining the genetic differentiation of wild populations. Limited work has been carried out on the population structure of tropical species. This affects the management of the populations, may have a detrimental effect on the fitness traits and may counteract the efforts of conserving the purity of the wild strains.

Hybridization

Hybridization can be a genetic improvement approach to obtain heterosis of some fitness traits. If hybridization is chosen as an approach for improving the performance of indigenous populations then there should be well established genetic characterization records in order to monitor the long term purity of the broodstock. The current domestication practices seem to promote the production of unplanned hybrids. Management protocols for handling the hybrids have not been outlined.

Collection of founder populations

The most important consideration during genetic material collection and management of the populations in stations is to conserve the gene pool to prevent genetic drift and detrimental levels of inbreeding in order to minimize changes over time in the gene and genotype frequencies.

Selection and testing of indigenous species

When testing strains there is need to compare their performance in various culture environments. The implications of the genotype-environmental interactions are that the estimation of the genetic parameters and evaluation of different strains of indigenous species should be carried out in close cooperation with farmers. The test environments should be similar to those of the farm environment. Some of the trials can be carried out in farmer's environments so that strains can be ranked in terms of their performance in various farms and this will enable the development of environment specific strains.

Introduction

Apart from numerous bio-technical factors that affect the selection of a species, there are also a number of social and economic factors which should be taken into consideration.

Macro-level factors

At the macro-level, factors which should be taken into consideration tend to be politico-economic rather than socio-economic. These factors broadly encompass issues arising from government policy both in the nationally and more specifically, of the fisheries and aquaculture sector.

Government policy

The government policy sets the development objectives which often include increasing living standards of the rural population, improved household food security and the development of the private sector. They often also include the identification of the main beneficiaries of development. The selection of a fish species should contribute to the achievement of the development objectives, and has to take into account whether the species is appropriate for the target group, both at a national and local level.

Implications of sectoral policy on research

The selection of species for aquaculture and fisheries will be partially determined by the resources available to carry out research on these species. These resources are allocated based on research priorities detailed in the government policy.

Implications of sectoral policy on extension and training

The priority accorded by governments will also influence the resources allocated to extension and training. Where resources are few, efforts are usually made to capitalize on existing structures, and selection of species will be influenced by what species are already available and which culture systems are already known.

Micro-level factors

Market

When selecting a species it should be acceptable for eating in terms of size, price, taste, preparation, appearance, bones, flesh, and religious and traditional beliefs.

Culture systems and target group

The type of culture system suitable for farmers, which in turn depends on the resources and needs of the target group, in a particular area is an important criterion for determining which species to select.

Small reservoir fisheries

Fishing activity around small reservoirs varies from subsistence, commercial to sport. The selection of species for stocking will depend on which type of fishery for which it is intended, and its effect on other people involved in the fishery.

Supply and cost of fingerling

Often, selection of a species for either culture or stocking is not carried out systematically, but based on what is available. Farmers do not always have access to knowledge about the best species to use, and therefore buy what is available rather than what is necessarily best.

A criterion for selecting species for small-scale farmers should be that it is easy to reproduce. Species which minimize dependence on external supplies of fingerlings are most suitable.

Evaluation of species

Cost/Benefit analysis

From an economist's perspective, evaluation of species can be carried out using cost benefit analysis. Whilst it is acknowledged that there are flaws in solely depending on this kind of analytical tool, it does provide a good indication of the relative benefits of species.

Codes of practice

Existing codes of practice for the introduction or transfer of species tend to ignore social and economic factors, and focus on the technical and biological aspects of an introduction. Questions covering government policies and objectives, target group focus, markets, extension capacities of government, fingerling supply and feasibility of culture systems could all be included in such a code.

Conclusions

Whatever the eventual method selected to evaluate a species, there are a number of critical social and economic questions which should be answered before an introduction or transfer occurs:

• Does the introduction/transfer fit into the existing government policies and legislation.
• Does the introduction/transfer contribute to the achievement of the national development objectives.
• Are there sufficient resources in terms of research, training and extension to support a transfer/introduction.
• Is there an existing market or potential market for the species.
• Are the target groups able to culture the species given their existing resource base.
• What impact will the species have on the different fisheries around a water body.
• Are fingerings available to support the utilization of the species.

Introduction

Malawian legislation prevents the import of exotic species within the Lake Malawi catchment area. Research into new species for aquaculture candidacy therefore has to be conducted with indigenous species. Most work has focused on the tilapia, Oreochromis karongae.

Taxonomy

O. karongae is one of the tilapias endemic to the Malawian waters north to the Murchison Rapids in the Shire river. It is a cichlid belonging to a monophyletic flock of the subgenus Nyasalapia. Other indigenous tasselled tilapias assigned to this subgenus are; Oreochromis lidole, Oreochromis saka and Oreochromis squamipinnis. These three species are collectively called Chambo.

Feeding habits

The juveniles of chambo species feed mainly on encrusting algae growing on rocks and macrophytes. When adults, plankton and sediments become important sources of food. It is believed that O. karongae exhibits a much wider dietary breath than the other Nyasalapia.

Selection of O. karongae

Prerequisite traits for aquaculture

Total length data showed that all three chambo species grew better than Oreochromis shiranus chilwae and Oreochromis shiranus shiranus in natural conditions of the open waters of Lakes Chilwae and Malawi. Growth of O. lidole, O. saka, and O. karongae compared well with O. niloticus and O. aureus.

Breeding and feeding biology would suggest suitability to the low input farming systems common to rural smallholders.

Culture of existing indigenous species

The dominant cultured species in Malawi are tilapias, O. shiranus, Tilapia rendalli and O. mossambicus. The latter is not cultured within the Lake Malawi watershed. O. shiranus and T. rendalli are noted for their precocious breeding behavior resulting in stunting and poor growth.

Decline of the Chambo fishery

The present annual chambo catch for Malawi stands at 3,872 tons for 1993, down from an all time high of 17,041 tons in 1984.

Summary of experimental work

Comparison with O. shiranus

No advantage in growth rate is gained by replacing O. shiranus with O. karongae in the 5–50 g mean body weight range under different culture conditions. At mean stocking body weights exceeding 40 g, growth rate of O. karongae was significantly higher then O. shiranus.

Inputs and stocking densities

Density effects of 4 fish /m² did not show a significant reduction in individual body weight gain compared to ponds stocked at 2/m² in the 4–45 g range suggesting the higher stocking density for greater total final biomass and more favorable economic returns.

Results from this trial also showed that O. shiranus produced much greater numbers of fry compared with O. karongae.

Growth performance in polyculture with Clarias gariepinus

The polyculture demonstrated that the average attainable extrapolated gross yield is greater than 50 kg/are/yr using maize bran at 3% total biomass per day and 7.3 and 4.3 kg/are/week of pig manure and chicken manure as inputs.

Reproductive biology

Little is know of the breeding biology of O. karongae. Fry collection was recorded during the months of November to March only.

Implications for aquaculture and small reservoir fisheries

For the production of ‘large’ fish (50–100 g) with adequate nutrient inputs, O. karongae exhibits a superior growth performance compared to O. shiranus. This implies that O. shiranus is still the most suitable indigenous tilapiine candidate for the smallholder applying less than adequate fertilizers to his ponds. O. karongae would be more suited to commercial operations or perhaps smallholders with sufficient input resources.

Recruitment of fingerlings in an O. karongae production pond when mean body weight of the original stock at harvest is 105 g is insufficient for restocking the same pond at a density greater than 1 fish/m².

Total net yields could also be boosted to over 50 kg/are/yr by combining O. karongae with C. gariepinus at equal densities of 2 fish/m² in a manure/maize/bran system.

Little is known of the potential gains or losses from stocking O. karongae in unmanaged small reservoirs. There are concerns of possible hybridization with O. shiranus. O. karongae could do well in deep dams, but pilot studies would be necessary to assess the causative factors of hybridization. If the addition of O. karongae is unlikely to substantially improve production of these inland impoundments and benefit surrounding communities, it is perhaps not worth the risk of genetic disruption and possible alternation of specific and genetic diversity.

Introduction

Clarias gariepinus is an extremely hardy and adaptable animal, facilitated greatly by its air-breathing abilities. The species can efficiently exploit a wide variety of food items and is able to withstand adverse environmental conditions and habitat instability.

Perhaps the most interesting feature of the catfish in terms of aquaculture is its capacity to thrive under high density conditions, without prerequisite pond aeration or high water exchange rates.

In Southern Africa, C. gariepinus has been recognized as a candidate aquaculture species since the early 1970s, but it was only in 1980 that a dedicated research program was initiated to develop the farming technology.

The history of catfish culture research in South Africa

The first commercial catfish farms in South Africa and Zambia were established in 1984, although success was only achieved some two years later. In 1988, the basic technology developed in South Africa for the commercial culture of African catfish was published.

The development of the industry and current status

Catfish are produced mainly in 0.1 ha. earthen ponds, although high density tank culture is gaining in popularity. The current production in earthen ponds is 40 tons per hectare per 8–12 month cycle. Under high density tank culture conditions production averages of 350 to 400 kg per cubic meter per ten months are achieved.

In South Africa production increased from ten tons in 1987 to a high of 1200 tons in 1990. Since then there has been a virtual collapse to around 150 tons in 1992. The collapse was a consequence of inadequate planning, a lack of marketing expertise and strategies, inadequate fiscal resources of farmers for marketing and product development and consumer resistance. A further compounding factor was a disproportionate increase in the cost of feed coupled with a near static farm gate price.

It is the opinion of economists and farmers alike that it is only a matter of time before the catfish industry will have a price advantage over sea fish. However, until this point has been reached and unless a dynamic marketing strategy is implemented, catfish farming will remain a marginal activity.

The future of catfish farming in Southern Africa

Biotechnologically the African catfish is undoubtedly the most ideal aquaculture species in the world. From its inception, the South African catfish farming industry was science and technology driven, with a perceived demand for the product. Absent from the equation however was a real market demand for the product. The most likely scenario for success lies in the predicted medium term increase in the price of sea fish. Once this has happened, African catfish will find its rightful niche in the market, and given the readiness of the technology, the industry will be able to satisfy any demand.

Introduction

Aquaculture and water resource management efforts have relied on a few well-established fish species. Most of these are exotic in many of the areas where they are used. The Malawi Department of Fisheries in collaboration with the University of Malawi and the International Centre for Living Aquatic Resource Management (ICLARM), is attempting to establish routines and protocols for the screening and testing of indigenous species for use in aquaculture and water resource management.

Among resource poor farmers in sub-Saharan Africa, pond inputs are the major constraint to increasing yields and increases in efficiency through polyculture might be especially important. Another problem for resource poor farmers is the lack of high quality fingerlings.

This study was to determine whether or not Barbus paludinosus and B. trimaculatus, commonly known as matemba, would grow and reproduce under conditions prevailing on local resource poor farms and to estimate what the production of matemba would be under these conditions.

Materials and methods

To determine if matemba could grow and reproduce in small ponds, three replicate 200 m² ponds were each stocked with 2,260 mixed B. paludinosus and B. trimaculatus.

Based on the stomach content analysis, it was hypothesized that Oreochromis shiranus and matemba would be compatible in polyculture. Ponds were stocked with poly culture and monocultures.

The market value of the various sizes and species of fish produced by each system was calculated based on information from four local markets.

Results

Over the course of 150 days B. paludinosu O. shiranus polyculture was significantly more productive than the monocultures of either O. shiranus or B. paludinosus. Productions were 1,006, 827 and 837 kg/ha respectively. Over the 107 days the B. trimaculatus O. shiranus monocultures and polyculture were equally productive, producing an average of 574 kg/ha.

Survival of O. shiranus from stocking to harvest was not affected by polyculture with B. paludinosus, but was significantly lower in polyculture with B. trimaculatus. Survival of matemba was not affected by polyculture.

Reproduction of O. shiranus and B. paludinosus was not affected by polyculture. Matemba reproduction was extremely variable, ranging from 327 up to 12,200 juveniles per pond.

The B. paludinosus O. shiranus polyculture generated 30% more income than the O. shiranus monoculture and 96% more income than the B. paludinosus monoculture. The B. trimaculatus O. shiranus polyculture generated 16% more income than the O. shiranus and 68% more than the B. trimaculatus monoculture.

Discussion

Polyculture of B. paludinosus with O. shiranus is obviously an attractive proposition. The case for B. trimaculatus polyculture with O. shiranus, however, is not so clear. Regardless of whether or not productivity was improved by polyculture, profitability was dramatically enhanced for both polycultures.

Small water bodies (SWB) form one of the most valuable sources of fish for rural communities in Malawi. There are over 700 small water bodies in Malawi, close to 75% of these are found in the southern region of the country. There are three categories of SWB; namely community, private and government-owned. Fish in these reservoirs have been stocked by either the government or private owners, using stocks from either lakes or the National Aquaculture Centre (NAC). Potential for stocking other fish species exists.

To date, the NAC has embarked on a program to search for candidate fish species for use in aquaculture. With the help of JICA, work has been carried out on mainly indigenous Lake Malawi cyprinids (Barbus johnstonii and B. eurystomus). Currently, NAC is undertaking survey of some ten SWBs in the southern regions. Predominant species in these SWBs are Oreochromis shiranus, O. chilwae, Tilapia rendalli, Sarotherodone robustus, Clarias gariepinus, and Barbus spp. Specimens of O. shiranus and T. rendalli of 300–600 g have been observed; and those of S. robustus of 900–1000 g have been noted. Other observation made include that:

• Much of the productivity seems to originate from the agricultural lands surrounding the SWBs. Thus, exploitation of these SWBs can be intensified taking advantage of the inflow of agricultural nutrients.
• Fish found are predominantly micro-feeders (Oreochromis spp.) and macro-feeders (Tilapia rendalli) and zooplankton feeders (Barbus spp.), thus leaving an unutilized niche on the bottom. The bottom and the weedy peripherals of the SWBs can be utilized by the larger barbus species.

Specimens of B. johnstonii and B. eurystomus are currently kept at NAC and were collected form Lake Malawi and the Upper Shire River. Future plans include undertaking artificial spawning in ponds, and limited introduction to at least three SWBs which have permanent rivers flowing into them. It is hoped that the species take up the niche left by the withdrawal of Cyprinus carpio in pond aquaculture and that they will establish populations in the SWBs to improve production.

Introduction

Although the fishery potential of small water bodies in the Central and Southern Africa is highlighted in many recent reports, development of such a fishery is on its infancy stage. ALCOM started some work in the Eastern Province of Zambia. In 1993–94 ALCOM, in collaboration with the Government of Malawi, carried out studies on two small water bodies in the south of Malawi. This paper looks at catch per unit of effort (CPUE) of Barbus paludinosus in this latter study. Further, food habits of B. paludinosus and their role to the food chain are suggested.

Materials and Methods

The small water bodies in this study were Mikolongwe (2.5 ha) and Mbvoniha (3 ha). Sampling of these small water bodies was carried out from February 1993 to March 1994 at a 1 to 2 months interval.

Results and Discussion

CPUE in both small water bodies was higher for B. paludinosus than Oreochromis shiranus. Results show that CPUE for B. paludinosus was also more stable than that of O. shiranus.

The peaks for CPUE for B. paludinosus and temperature coincided. The high temperatures increase mobility of the fish and hence the catches of the gillnet.

The common species in small water bodies are B. paludinosus, O. shiranus, and Clarias gariepinus. B. palidinosus depended more on zooplankton (56%), along with non-filamentous green algae (19%) and higher plant material (14%). O. shiranus' diet was predominantly of plant form (higher plants and phytoplankton).

The diet C. gariepinus varied with size of fish, ranging from zooplankton for small fish to fish remains for larger individuals.

From diet composition of the species, it can be noted that the feeding habits are complementary to each other.

Conclusions

Handling stress problems of transportation may make B. paludinosus unsuitable for small-scale fish farming. However, B. paludinosus is a potential candidate for small water bodies fisheries. This calls for detailed study of population dynamics and other related areas to obtain maximum economic returns from the species.

Introduction

To date, agriculture in Malawi has relied heavily on tilapia. Fish consumption in Malawi has declined over the past decade mainly due to the static if not declining fish landings from capture fisheries.

The Malawi Government is reluctant to introduce exotic fish into its waters for fear the introduced fish would destroy the rich natural fauna. Research is therefore required in order to find suitable fish for aquaculture among the endemic species. Observations point to the fact that Clarias gariepinus and Bagrus meridionalis are worth investigating for the possibility of adapting them for aquaculture in small water bodies in Malawi.

In Malawi, the aquaculture research stations at Domasi and Mzuzu have successfully bred the C. gariepinus. C. gariepinus grows well in fertilized static ponds. C. gariepinus converts feed into growth better than tilapia and growth rate to market size is more rapid than that of cichilds in general.

Conclusion

The African catfish C. gariepinus is endemic in Malawi waters and in acceptable as a table fish, mainly in dried form. Its hardiness in terms of tolerance of low dissolved oxygen and survival at high stocking density makes it a good candidate for aquaculture.

Project Development Background

About 25 cyprinid species occur in the Lake Malawi, most of which are either endemic riverine or andromous. Two of these species, mpasa (Osparidium microlepis) and ntchila (Labeo mesops), support, or have previously supported, important commercial fisheries. Populations of all the obligate river-breeders are in decline as a result of overfishing and loss of spawning habitats through siltation and degradation of perennial streams.

The mpasa is one of the favourite fish species in Malawi, fetching premium prices in local fishing markets. As recently as 1950s the ntchila was the most important species landed in Malawi. Since the 1950s, catches of ntchila from the Lake have declined from 14.7% to 8.2% in 1962 and 0.3% in 1989. The main reason for the decline is increased exposure to fishing pressure during the spawning season.

Efforts are being directed at searching for suitable candidate species for aquaculture in Malawi. There are several reasons why the endemic cyprinid species in Lake Malawi are potential candidates for aquaculture. These are:

• marketability, cyprinid species are considered by the people to be most desirable fishes;
• high growth rates;
• rase of artificial breeding;
• biological diversity.

Project Objectives

The project will have the following specific objectives:

• to protect the cyprinid species of Lake Malawi, by enhancing their population in the lake, by releasing into the lake or small water bodies, artificially hatched juveniles;
• to promote aquaculture of these cyprinid species of Lake Malawi, by enhancing their population in the lake, at a viable cost;
• to facilitate training needs for Malawi Fisheries Department, and Bunda College of Agriculture, University of Malawi.

Project Phasing

The first five years of the project will be pilot phase. This phase will undertake biological studies as well as feasibility study for broodstock management, hatchery operations, feed development and cage culture.

The distribution patterns of 42 aquatic animals which have been introduced into catchments beyond their native range are examined. The environmental impacts of the most undesirable species are discussed as well as the original reasons for the importation of these species.

Biogeographic analysis of alien species assemblages in catchments gives indication of the degree of invasion in each catchment.

Recommendations are made concerning catchment management and the design of decision protocols relating to the importation of alien species.

The use of exotic species has been an effective means to increase production from aquatic systems and generate income. However, the impact of exotic species on both the biological and social environment has often been unexpected and not always positive. In an effort to maximize benefits from the use of exotic species in Southern Africa, a code of practice developed in Europe and North America by ICES and EIFAC was examined for its applicability to the region. The regional elements and principles of the ICES/EIFAC codes promote a prior evaluation and planning of any movement of aquatic species. It is felt that these can be applied, to a certain extent, in developing countries and rural areas.

Elements of a generalized code include the following steps:

• a proposal to import a specific species including the planned use, location of culture facility or receiving water body, passport information on the species, any special concerns or problems associated with the species and the source of the species;

• an independent review of the proposal including an evaluation of disease organisms associated with the exotic species, ecological requirements/interactions, genetic structure and hybridization potential, socio-economic considerations, and specific local species that may be impacted; and

• the provision of advice by review board to appropriate authorities and prospective importer.

If the review and advice offered indicate that the use of the exotic species is warranted and approval to import is given, then post-import protocols for the importer and resource manager would include; a) quarantine, b) confinement, c) monitoring and d) evaluation.

This generalized code is discussed in terms of its suitably to Southern Africa and the Convention on Biological Diversity.

Introduction

In response to the need for a precautionary approach to the introduction or transfer of aquatic organisms, various bodies, mainly in North America and Europe, have developed codes of practice relating to the activity. These codes have proved valuable in addressing the potential risks and benefits of the introduction or transfer of aquatic organisms leading, through a decision making process, to rational conclusions as to whether the proposed introduction or transfer should occur, and by what mechanisms. FAO is currently drafting guidelines for the introduction and transfer of aquatic organisms.

This paper will focus on the principles involved and especially outline the mechanisms required in order to implement the guidelines or an existing code.

Principles involved

There are two fundamental reasons for using a “code”: (1) to limit the impacts of the introduction/transfer on biodiversity and (2) to attempt to ensure that the introduction/transfer meets socio-economic development goals.

The principle of the procedure involved is quite simple. When there is a proposal to introduce or transfer an aquatic organism it is subject to evaluation (before it occurs) followed by an independent review of the evaluation and a decision on whether or not to proceed with the introduction or transfer (and by what means, e.g. quarantine considerations etc.).

Definitions of introductions and transfers - when do you need to use a code or guidelines

The definition of an introduction is the release of a species outside its natural range; an exotic species is a species that does not naturally occur in the region in question; a native species is a species that occurs naturally in the region.

Legal context and evaluation, review and decision making infrastructures

Countries should ensure that they have their own effective domestic legal frameworks by which they can control and manage introductions and transfers. The proposal may involve the movement of organisms internally. Therefore it is necessary to adopt a local system that requires all people or institutions involved in moving live aquatic animals, including internally, to request approval from the appropriate decision making body in question.

Ideally, an appropriate evaluation should accompany the proposal when it is sent to the decision making body for consideration.

The evaluation process obviously involves the compilation of data on the potential effects of the proposal and undertaking further studies or research if and when necessary. This must include all aspects, both negative or positive, of the proposal and be thorough enough to enable a rational decision to be made.

The review process analyses the proposal and its evaluation and makes recommendations on their suitability. This might be a recommendation to approve or reject the proposal or may involve a recommendation to undertake further evaluation.

In all cases it is essential that an independent review of the proposal and its evaluation are made.

It will be rare that all parties in the review panel will agree totally with all aspects of a proposal and its evaluation. The result of a review must be based on a consensus of informed and unbiased opinion.

Normally a decision or approval to introduce or transfer will be made legally by a discrete entity, for example, a head of a department, or a politician. In these circumstances, the purpose of the above process is to ensure that final decisions are based on a consensus of informed opinion.

Aquatic organisms released will pay little attention to political boundaries between countries. Due to the extent of shared river basins and lakes that exist in Africa, this is likely to be an issue with many proposals. Where release will occur into shared habitats then representation from the other country(s) in question should be included in the review and decision making process.

Summary and Conclusions

Apart from forming an extremely useful framework under which to undertake an evaluation of the pros and cons of a proposed introduction or transfer, there are other advantages to the adoption of a code. Its existence can often rescue persons or institutions from difficult situations; because it can be argued that it was the “code procedures” that resulted in disapproval of a suggestion. The most powerful aspect of using a code is to screen out the less logical proposals at the outset.

The code is a tool, not a regulation. Those who start the process with a desire to encourage a certain outcome need not bother using the code at all.

What is recommended is that countries adopt a responsible approach to introductions and transfers. Using the framework as outlined here is a good way of achieving this aim. Countries will need to develop their own circumstances. These can only be developed and improved through experience.

At a commercial fish farm near Banket, Zimbabwe, fattening comparison trials between Oreochromis mossambicus, O. macrochir, O. niloticus and a O. macrochir/niloticus cross were carried out.

Fish of 25 g, were stocked in circular 20 m³ tanks at densities of 1500 fish per tank, water flow was maintained at one liter per kg of fish per minute. Fish were fed 10 times per day for six out of seven days. Fish were harvested after 140 days.

The results showed significant differences in food conversion rates for gutted weights. O. niloticus achieved much better production results. (FCR 2.17) than the other species. The cross of O. niloticus and O. macrochir produced better (FCR 3.02) than the pure O. macrochir (FCR 3.90) or the O. mossambicus (FCR 3.78).

Growth performance in cages further improved the production due to:

• constant selection of rapid growers;
• better oxygenation in the open water;
• more efficient removal of fish waste;
• improved feed quality;
• change in feeding rates.

The author feels that all male Tilapia rendalli culture could perform as well as O. niloticus.

Kafue Fisheries Ltd is a 23 hectare integrated pig-fish system established in 1981.

The indigenous tilapias species Oreochromis andersonii looked the most promising and the pig-fish regime showed superior performance to other systems tried. Clarias gariepinus fulfuls the role of controlling indiscriminate breeding amongst the tilapias.

Other species have been tried, with the most notable success being Cyprinus carpio. The main advantage of carp is that they are a species which can be managed and controlled far more easily than the tilapias. The main disadvantage is that of market resistance. Pond bank damage is a further disadvantage. The project sees C. carpio as a complementary species rather than a competitive one with O. andersonii.

The selection process for O. andersonii has always followed three basic criteria:

• maintaining the purity of line;
• the selection of individuals with the fastest growth rate under comparable conditions;
• the selection on late maturity.

This selection process has been going on for 13 years. The carp has been domesticated and been subjected to selection pressure for hundreds of years and it is for this reason that they do have a place for the commercial producer who is able to provide the correct infrastructure and has access to supplementary feed in adequate quantities. The tilapias on the other hand, because of their hardness, ease of propagation under natural conditions and their ability to grow under a wide range of feeding systems, make a more suitable species for small-scale farmers. Furthermore, with vegetable material being the most accessible source of feed to most small-scale farmers, more attention should be paid to herbivorous species such as Tilapia rendalli.

In Malawi, the common carp was introduced in 1976 after three indigeneous species failed to produce high yields during a three to four year experimental work at a government station. However, the initial introduction was not without restrictions.

The indigenous fish species that are raised in Malawi are Oreochromis shiranus chilwae, O. mossambicus, Tilapia rendalli, Claris gariepinus and O. karongae.

The introduced exotic fish species are trout, Salmo trutta, and three carps - common, grass and silver although the last two failed to establish themselves and only the common carp is currently used.

By 1984, the Fisheries Department formulated conditions for distribution of common carp to farmers. It was categorically stated that only farmers outside the Lake Malawi catchment area would be allowed to breed the fish; all carp fingerlings were to be supplied from the two government fisheries stations in the southern region of Malawi “away” from the Lake Malawi catchment other than the Shire River.

Considering that the carp was distributed to some farmers away from the Lake Malawi catchment area, it would be unwise to abruptly ban the carp. Considerations should be given to concentrating the carp in areas sufficiently known to have no direct connections to Lake Malawi and other major lakes and river systems. The reasons for restrictions would be adequately explained to the farmers and extension staff in the field. It would appear the common carp issue needs not only to be discussed at a national workshop but at a regional workshop. The carp has been used and/or is being used in fish farming in at least seven of the original ten SADC countries.

If we are indeed to sustain aquaculture development in the region there should be strong urge to study the indigenous species and determine which ones would be suitable for small reservoir fisheries and aquaculture in Southern Africa.

The objective of the Fish Culture Development Project in the Northern Province of Zambia, in operation since 1988, is to introduce and support fish culture activities among interested farmers of different backgrounds, who have suitable sites to construct fish ponds and are prepared to follow the recommendations of the project staff.

This paper summarizes the main aspects and reasons why certain fish species (red breasted bream, Tilapia rendalli, Kafue bream or three spotted bream, Oreochromis andersonii and green headed bream, Oreochromis macrochir) are produced and distributed widely, why common carp, Cyprinus carpio, is planned to be distributed in a limited quantity, and why other species (silver carp, Hyphothalmichthyes molitrix, big-headed carp, Aristichthyes nobilis, and grass carp. (Ctenopharyngodon idella) are not planned to be produced and distributed to the fish ponds of the province.

The conclusions are:

• Local breams (T. rendalli, O. andersonii and O. macrochir) are recommended for all existing fish farmers of different technical and financial background.
• Common carp is not recommended to the fish farmers of the province. However, because of the pressure of the farmers, it is agreed that this fish species would be sold to farmers of the province whose fish ponds are suitable and who are aware that conducting fish culture management on an adequate level is a basic requirement of rearing common carp.
• Chinese carps need fish culture management at the advanced level. Chinese carps have therefore not yet been recommended to be introduced into the fish ponds of the province.

Unless new considerations demand the immediate introduction, Chinese carps are not envisaged to be introduced and produced in the fish ponds of the province in the near future.

By the time the production conditions at farmer level are favourable for the introduction and production of Chinese carps, the presently cultured species or other, native fish species may be found to be suitable and reach similar productions. However any of the above options require consistent, dedicated and collaborative work from both the fish culture and the natural fisheries professional staff of the province.

Introduction

The translocation of exotic aquatic organisms is invariably accompanied by the potential to introduce diseases, disrupt the ecological balance and degrade some benefits from the aquatic resources. Most literature however tend to report on the impacts from country to country movements with very few examples of indiscriminate movements between catchments within the same country.

The Zimbabwe case study

Zimbabwe has ten distinct river systems. The presence of physical and ecological barriers has resulted in partially different aquatic species above and below these barriers.

Although all importations/translocations should be made under adequate national control and surveillance supported by an adequate framework of laws and regulations, many of the introductions/translocations were not in compliance with the established guidelines of tranfers and introductions. Despite stipulated regulations, some indiscriminate introductions have occurred.

Over the years, the Department of National Parks and Wildlife Management (DNPWM) and Agritex Fisheries Unit have been stocking waters within the country and have transfered a number of fish species from their native river systems.

Translocation of fish species around Zimbabwe

Status of translocated indigenous fish species

Oreochromis macrochir and Tilapia rendalli are indigenous to Zimbabwe but did not occur in most of the ten river systems. Their natural distribution was poorly understood such that a lot of transportation of these species have occurred outside their natural range.

O. macrochir only naturally occurred in the Upper Zambezi but is now found in seven of the ten catchment areas. The transportation of the species into many ponds throughout the country overlooked that fact that the species did not occur naturally outside the Upper Zambezi catchment area. The reasons for translocating O. macrochir were mainly to increase the productivity of reservoirs. The DNPWM selected O. macrochir as an important candidate for aquaculture and moved it to research stations around the country.

T. rendalli only naturally occurred in the Zambezi and Lundi systems. Fisheries records now show that T. rendalli is now in all of the ten river systems. Because of its feeding behaviour, the fish was mainly used to control weeds. It is now one of the popular aquaculture species.

Status of translocated exotic fish species

In 1925 Cyprinus carpio was introduced into Matopos dam. In the late 1930s carp was declared undesirable and further introductions were prohibited. In the late 1950s mirror carp was introduced to Mazowe and Savory dams where they did so well that many farmers all around the country stocked these carp into their farm dams.

Largemouth bass, Micropterus salmoides, was introduced and spread rapidly to most of the DNPWM research stations from where they were translocated into five of the ten catchment areas. To date, bass is widely distributed over the whole country without any restrictions on its movement.

The original introduction of O. niloticus was controlled by permit only. However, once in the country, it has now been translocated to many other farms and is found in several river systems.

Discussion

Rules exist for introducing fish into a country, but fish do not stick to human boundaries. There are much fewer restrictions and controls for translocating fish within a country, whereas introductions should in fact be regulated by river system and agreed upon by all countries connected to that system.

Introduction

Crayfish was introduced into Zambia in 1979 from Lake Naivasha in Kenya. The species introduced was the North American red swamp crayfish. Procambarus clarkii. At present, the farm in Zambia has two more species the redclaw, Cherax qaucricarinatus, and the yabbi, Cherax albidus.

P. clarkii grows to a size of around 75 g and the small size is a problem for marketing. The redclaw, which grows to a size of 200 g in 15 months, can tolerate high temperatures and be held in high densities in tanks, would be a better candidate for commercial culture. The yabbi is also recommended for culture in Zambia due to its tolerance of extreme temperatures.

In Zambia there is at the moment no real market for crayfish and education of hotel staff will be necessary to develop this market.

Predation

Predation of crayfish is a serious problem in Zambia. The main predators are catfish, otters, Nile monitor lizards and birds like herons, cormorants and kingfishers.

Environmental impact

The author expects that, due to the high predation pressure on crayfish, any accidental escape into natural waters will have no significant impact. The crayfish will not be able to establish a population. If the crayfish would establish, as happened in Kenya, the author states that this may have beneficial impact as the crayfish will control the snail population and help to erradicate bilharzia. Besides, the opportunity from export would be beneficial to the economy of Zambia.

Background

New Guinea is the world's largest tropical island and has extensive areas of freshwater habitat. The kinds of fishes dominating freshwater fish faunas in other regions do not naturally occur here. The fauna is composed of representatives of marine families. Yields from the country's largest river are less than 10% of those obtained from similar systems in Africa.

In 1983 it was proposed that one way of improving the fishery in the Sepik Ramu basin was to introduce more species of fish.

Brief review of activities

Codes of practice

At the outset, it was decided by all parties that the project would implement existing codes of practice regarding the introduction of aquatic species. However, several attempts were made to stop the project. This initial barrage of criticism was weathered on the grounds that the project was adopting a precautionary approach and was following the codes.

Research/evaluation activities

When considering the introduction of an exotic species it is essential to have a good, broad understanding of the resident aquatic fauna of the region in question. By utilising existing maps of the region, a database was compiled on the area's aquatic resources.

A database on population distributions was also compiled using existing population censuses. By utilising existing sources of data, a picture of the socio-economic status of the entire population was obtained, including regional variations. Existing data sources were very limited on fisheries related activities and the project had to collect much of this data via field censuses in selected and representative areas.

Formulation of management plans

Biological and ecological studies on the fauna and flora, with emphasis on fishes, outlined the current extent of utilization of the trophic opportunities available in the river system. It was shown that the river basin was devoid of adequate fish resources for reasons of its zoogeographic location and the absence of suitable breeding grounds for many of the species occurring in nearby areas.

Socio-economic data indicated a large involvement in fishing throughout the region. Over 95% of the population live in rural areas and are still essentially hunters and gatherers and subsistence gardeners. Over 95% of the population live within 0.5 km of and usually adjacent to good water resources quite capable of supporting significantly improved fish stocks. Combining demographic data and aquatic resource availability enabled an assessment of potential fishing pressure throughout the catchment.

Implementation of management plans

An approved list of suitable species for stocking was gradually compiled. This centered on the concept of minimal theoretical ecological impact and maximum benefit to the fishery.

The first fish imported, introduced and stocked was Tilapia rendalli. It was selected because of the ease of obtaining fingerlings and an anticipated short establishment time leading to quick tangible benefits.

The Department of Fisheries had no powers over fish imports. This resulted in inexperienced and unqualified individuals from another department being able to undermine the project. The need for important internal decisions to be made by the most appropriate authority was thereby highlighted.

Perspectives for Southern African countries

In some aspects, the Papua New Guinea experiences are unique. There is a significant natural problem due to the inappropriateness of the native fauna for fisheries development. This, together with the extent of freshwater resources available, population distributions, socio-economic conditions and cultural systems presently in place, provided proven, clear and substantial benefits from a stocking programme. In addition, the project has been lucky to benefit from funding sources willing to accommodate relatively expensive and lengthy pre-introduction evaluations. In countries in the Southern African region, factors will be significantly different. Nevertheless, some useful comparisons can be made.

• Codes of practice. The main conclusion from our experience is that the codes work. Apart from being a framework for rational evaluation, they also provide an air of responsibility and respect whereby potential critics can at least see that a precautionary approach to a problem has been adopted.
• Aquaculture versus stocking. The environmental issues between aquaculture and stocking, in terms of the effects of alien biota on resident fauna and flora, differ less. Species used for aquaculture will inevitably escape. In this respect, there is no difference between importing (or moving) a species for aquaculture and importing (or moving) it for purposeful release into the environment (stocking).
• Native versus exotic spares. In Papua New Guinea all fish species being stocked are exotic species. It should be noted that the use of native/indigenous species does not necessarily mean that the environmental consequences are any less severe. The transfer of native species can, sometimes, be even more damaging than using exotic species in that it is often certain that genetic mixing between transferred and resident species or strains will occur.
• Determine the extent and type of aquatic habitats available. Knowing the extent, type, availability and location of aquatic habitats is essential to formulating rational management plans. A logical introduction or transfer requires a significantly large potential benefit.
• Determine population distributions and cultural and socio-economic conditions. Socio-economic factors are perhaps the most important consideration with any programme involving the introduction or transfer of aquatic species. It is the potential benefits for people that should tip the balance for or against an introduction or transfer in most cases.
• Monitoring. Especially when dealing with small-scale or non-formal fisheries or aquaculture projects, adequate monitoring of developments is crucial. The lack of supportive data on the benefits of stocking is a major reason why such programmes are often viewed negatively by funding and planning agencies.

Conclusions

Perhaps the most internationally significant aspect of the Papua New Guinea experience is that it has conclusively shown, contrary to a widely held belief, that fish introductions and sustainable development are not necessarily mutually exclusive. Throughout the process of introducing fish species the code of practice has been indispensable.

Introduction

In spite of an already rich and diverse fish genetic resources of India, more than 300 exotic species have been introduced. The silver carp, Hypophthalmichthyss molitrix, and three varieties of common carp, were brought into the country with the objectives of broadening the species spectrum in aquaculture and increasing the yield through better utilization of tropic niches.

Role of silver carp in reservoir fisheries of India

Most of the reservoirs in the region sustain a long food chain fishery dominated by predatory catfishes. Some of the reservoirs are well protected by the presence of up- and downstream dams which prevent straying of silver carp into the river systems. Nagarjunasagar, a large impoundment on River Krishna comes under this category. At present, the annual yield of Nagadunasagar is of a very low order (2.5 kg/ha) with the major carps constituting less than 5% in the total catch. Based on limnological evidence, the reservoir should have a fish yield of the order of 90 kg/ha. Taking into account the hundreds of reservoirs belonging to this category, silver carp can be considered for selective stocking in Indian reservoirs.

The main apprehensions regarding the introduction of silver carp in India revolve round the following:

• Silver carp and catla share more or less the same ecological niche.
• Silver carp, being a coldwater fish with eurythermal adaptability, is likely to operate at a higher metabolic pitch in warmer Indian conditions.
• In feeding habits, it consumes about thrice as much as catla with no evidence to prove that its food conversion efficiency is superior to catla. Its higher food intake, faster growth and early maturity would give it an edge over catla in competition.

Positive aspects of the introduction can be summarised as:

• Essentially a primary consumer, silver carp converts the primary energy into fish flesh more efficiently that any other fish available.
• With its reported ability to feed on Microcystis, the ubiquitous plankton of Indian reservoirs, it can lead to a many-fold increase in fish yield.
• Any loss of catla fishery on account of silver carp will be amply compensated with the increased availability of fish in economic terms.
• The fears regarding the extinction of catla are not well founded as the silver carp did not breed in any of the reservoirs except Gobindsagar where the environment is totally unique.

Conclusions

It is a fact that the silver carp enjoys an advantage in its competition with catla. It can be instrumental in increasing the fish yield from Indian reservoirs considerably, by filling the underutilised niche of phytoplankton feeder, especially feeding a Myxophyceae. The economic gains accrued from the increased productivity have to be given due consideration in making the decisions to introduce the fish in reservoirs.

Significantly, despite its entry into a number of Indian reservoirs by accident or otherwise, silver carp failed to get naturalised anywhere except Gobindsagar. Considering that this reservoir, with its temperate climate, is closer to the original habitat of the fish and has a distinctly cold water hypolimnion due to the discharge from Beas, the silver carp seems to have found a congenial habitat for growth and propagation. Although introduction of silver carp was never cleared by the Committee of Experts constituted by the Government of India, the fish has been stocked in a number of reservoirs in the country. Nowhere did the fish propagate itself and make an impact as it did in Gobindsagar. Therefore, fears regarding the threat of extinction of catla from the Gangetic and peninsular India are perhaps misplaced.

Two main areas of interest of the World Health Organization are: introduction of aquatic species for biological control of snail intermediate hosts of schistosomiasis and the role of aquaculture in introduction, spread and aggravation of schistosomiasis and foodborn trematode infections.

The converse is certainly true, that most persons involved in research and control related to malacological aspects of schistosomiasis or the parasitological aspects of foodbom trematode infections are not aware of, nor have an ongoing dialogue with, those in the aquaculture sector. This review intends to provide some limited information to aquaculture specialists in anticipation of improving information exchange and collaborative field activities.

Conclusions

Biological control of snail intermediate hosts of schistosomiasis has been extensively studied without demonstration of consistent success. Introduction of aquatic species for this intended purpose is not recommended by the World Health Organization for public health control activities.

Poorly managed aquaculture systems represent a significant risk of introduction, spread or aggravation of schistosomiasis, malaria and filariasis. Control of transmission is possible with tested methods of environmental management. Freshwater fishborne trematode infections represent a future challenge for aquaculture systems in Asia, as yet there is no evidence that these are problems in Africa.

Over the years several experiments on the hybridization of Oreochromis andersonii and O. mossambicus crossed both ways have taken place at the government fish farm in Chilanga, Zambia, which resulted in the loss of the pure strain of the species of O. andersonii on the farm. As previous research done in Chilanga had shown that O. andersonii was the most promising tilapia for the use in pond culture, and it was decided in 1981 to go back to the Kafue River to collect specimens of the pure natural strain of O. andersonii. The farm ponds were gradually restocked with the new strain.

Kalimba Farm was originally stocked in 1985 with O. andersonii of the new strain coming from Chilanga Fish Farm. No other tilapia species has ever been artificially introduced on the farm. The farm has consistently produced a yield of 6 tons/ha/year on average with some ponds producing up to 12 tons/ha/year.

Bighead carp, Aristicthys nobilis, grass carp, Cthenopharrynngodon idella, and silver carp, Hypopthalmichthys molitrix, fingerlings were introduced into Mozambique from Cuba in October 1991.

A study on the potential impact of Chinese carp introductions into Mozambique was carried out that concluded it was unlikely Chinese carps would establish wild populations because they rarely bred outside their native range.

It was therefore recommended that Chinese carp could be utilized for weed control and fish production. However, due to ecological sensitivity of the Lake Niassa catchment area and possible impacts on the endemic fauna of the Lake, it was recommended that every effort should be made to exclude them from this area. By no means should these fish should be introduced in areas above the Zambezi River.

Conclusions

• The Chinese carp had very good growth.
• Two year old silver carp had good sexual development and spawned well.
• If during 1994 – 1995 the production and development of fingerlings is promising, it might be possible to expand its production area to other places.