The Department of Fish Culture within the Ministry of Agriculture of Mozambique has proposed a pilot scale project on the use of Chinese carps, i.e. the grass carp, Ctenopharyngodon idella, the bighead carp, Aristichthyes nobilis, and the silver carp, Hyphothalmichthyes molitrix, in order to increase food production from fish farming and stocking reservoirs. In addition, grass carp are proposed to be introduced into irrigation canals in order to control the growth of aquatic weeds. Although the culture of Chinese carps has proved beneficial in many parts of the world, these species are not native to the southern African region and may adversely impact local aquatic communities and the human communities that exploit them.
In order to evaluate the proposed project on the introduction of Chinese carps a three week consultancy was undertaken in association with an FAO Regional Aquaculture Programme, ALCOM, the Department of Fisheries, Zambia, the Department of Fish Culture, Mozambique and the Fisheries Department, FAO, Rome, Italy. During this consultancy five reservoirs and lakes, seven government fishery facilities, and 11 private fish farms were inspected in Zambia, Zimbabwe, and Mozambique. In addition, several small local fish markets and an extensive irrigation scheme were toured in Mozambique. Interviews were conducted with resource managers, fishery scientists, fishermen, fish vendors, aquaculturists, and FAO professional staff on the attitudes towards introducing Chinese carp and on the feasibility of utilizing Chinese carp in the Region. Reports by ALCOM professional staff and FAO consultancies on introduced fish in the Region were also reviewed.
The use of exotic fish as a means to increase fishery and aquaculture production has been an accepted practice for centuries if not millennia. The Chinese carps, i.e. the grass carp, Ctenopharyngodon idella, the bighead carp, Aristichthyes nobilis, and the silver carp, Hyphothalmichthyes molitrix, have been introduced throughout the globe (Welcomme 1988) and have contributed to increased food production through the efficient utilization of resources and available habitat. In addition, the grass carp, due to its herbivorous feeding habit, has been utilized as an effective control for a variety of aquatic vegetation (Chilton and Muoneke 1992, Wynn 1992, De longh et al 1993).
In light of the positive attributes of Chinese carp polyculture and weed control by grass carp, fry of grass, bighead, and silver carps were introduced from Cuba to the Umbeluzi Aquaculture Station near Maputo, Mozambique in October of 1991. The Department of Fish Culture, Ministry of Agriculture plans a pilot scale hatchery and grow out project where Chinese carps will be raised as food fish and grass carp will be stocked in selected irrigation canals for aquatic vegetation control. This pilot project is expected to help increase food production through the promotion of the culture of Chinese carps and to provide cost effective means to control aquatic vegetation.
However, introductions of non-native aquatic species, either directly into the wild or indirectly through escapes from aquaculture facilities, will often result in changes in native aquatic communities, as well as in the human communities that fish, farm or market aquatic resources; some of these changes may be unexpected and unfavourable. The introduction of crayfish from North America to Europe introduced a fungus that has decimated European crayfish stocks. The introduction of rainbow trout, Oncorhynchus mykiss, throughout the western United States, has reduced local aquatic invertebrate fauna and has seriously threatened other species and subspecies of salmonids. The introduction of the Nile perch into Lake Victoria has changed the primarily small scale artisinal fishery into a multi million dollar commercial fishery that supports industrialized processing and exportation ventures.
To date, few adverse effects have been reported on the use of silver and bighead carps. The literature on the specific effects of introductions of grass carp as a means to control aquatic vegetation is extremely contradictory and varied. However, changes in the local aquatic faunal community generally followed the removal of aquatic vegetation. Recent reviews have stated that the positive aspects of weed control by grass carp outnumber small changes in aquatic communities (Chilton and Muoneke 1992, De longh et al 1993).
Negative aspects associated with the introduction of Chinese carps are generally not expected due to the fact that this group of cyprinids generally does not reproduce well in the wild outside of their native in China and the Amur River drainage in the former Soviet Union. However, these carps are fairly long lived and strong swimmers capable of extensive migrations and have established reproducing populations in the lower Mississippi River system, the Missouri River, two Rivers in Mexico, Japan and the Danube River in Eastern Europe (Chilton and Muoneke 1992).
In an effort to maximize the benefits and minimize adverse environmental and socio-economic impacts from the importation of exotic species, professional fisheries societies, government ministries and inter-governmental bodies have instituted various regulations and codes of practice on the responsible use of exotic species. Foremost in this regard are the ICES/EIFAC Codes of Practice and Manual of Procedures for Consideration of Introductions and Transfers of Marine and Freshwater Organisms, hereafter called the Code (Turner 1988). FAO and other inter-governmental organizations are beginning to promote the Code through increased awareness building and refinement in order to facilitate utilization in rural and developing areas. Realizing that the Code will be difficult to implement in many of these areas, there is an effort to improve both the utility and practicality of the Code. None-the-less, it is the current policy of the Fisheries Department, FAO to apply the Code, to the extent possible, in FAO-assisted fisheries and aquaculture projects that are considering the use of introduced species.
Although the original importation of Chinese carps into Mozambique was done with minimal consideration of the Code, some disease inspection procedures were performed. These fish are now nearly two years old, in satisfactory condition, and the Fish Culture Department, Ministry of Agriculture plans a feasibility study on the use of Chinese carps in Mozambique. At present, the Fish Culture Department, Mozambique and an FAO Regional Aquaculture Project, the Aquaculture for Local Community Development Programme (ALCOM), in conjunction with the Fisheries Department of FAO, Rome, wish to evaluate both the proposed pilot study and the use of Chinese carps in Mozambique. This report summarizes a three week consultancy in southern Africa on the use of Chinese carp in the Region and proposes recommendations specific to the pilot project proposed in Mozambique.
A five step plan to evaluate the introduction of Chinese carps to Mozambique was devised:
Review aquaculture activities in the Region, i.e. Mozambique, Zimbabwe and Zambia, especially in regards to use of exotic species (Tables 1 – 3).
Consult with Regional fish farmers, resource managers, and ALCOM professional staff on issue of Chinese carp introduction.
Consult with local fish farmers and fish vendors to the extent possible on the acceptance of Chinese carps by local community.
Review record of exotic fish introductions into the Region, drawing on FAO data base on international introductions and reports of Dr Dirk F.E. Thys van den Audenaerde and Dr Brian E. Marshall.
Review and apply to the extent possible the ICES/EIFAC Codes of Practice and Manual of Procedures for Consideration of Introductions and Transfers of Marine and Freshwater Organisms (the Code).
Aquaculture activities in Zambia are summarized in Table 1. The aquaculture sector is comprised of three levels: 1) commercial scale farmers with strong financial backing often owned by multi-national corporations and operated by expatriates, 2) mid level farmers, and 3) small scale village and family farms. Tilapia, especially Oreochromis andersonii, are the most important species cultured, although catfish and common carp are popular in some areas. Many cultural barriers exist that prevent the wide-spread culture of species of catfish (Clarias spp. and Heterobranchus longifilis), e.g. there are aversions to scaleless fish, to fish that have “a human look”, and to fish that “look like snakes”.
There is a strong desire from the commercial farmers (level 1) to increase the culture of common carps, Cyprinus carpio, including the mirror carp strain which has reduced scales, and to introduce Chinese carps. This desire stems from the fast growth of carps, a perceived market demand for large fish (1 kg), and the belief that carp will command a higher market price than tilapia. Some mid level farmers (level 2) may also be interested in and capable of culturing carp.
Grass carp is the only Chinese carp to have been introduced, although common carp has been introduced a number of times and is currently cultured in several farms. Grass carp were introduced to the Mubuyu Farm where they were induced to spawn by hypophysation (injection of pituitary extract). Fry were stocked into earthen ponds, but were apparently preyed upon by local catfish (Clarias spp. and Heterobranchus longifilis), as no carp survived. Currently there are reportedly no grass carp at this farm (Mr Mimoss Miyoba, hatchery technician, pers. comm.).
In the 1980's grass carp were also imported from Mauritius to Chilanga by the Fisheries Department. In November 1992, only 9 of these fish remained at the Fishery station. However, subsequently all have died as a result of road construction and diversion in the vicinity of the culture facility. In light of the limited introduction and limited survival of grass carp in Zambia, it is not surprising that no adverse impacts have been reported.
Common carp are cultured in several areas and the strain of common carp known as mirror carp, because of reduced scale pattern, is cultured and distributed by the Department of Fisheries' Mwekera Hatchery in the Copperbelt region. There are currently 300 names on the Mwekera hatchery's distribution list, of which about 100 receive fish. Although it was reported by several farmers that no common carp were present in the Kafue River or in Lake Kariba, that this species would probably not establish reproducing population in Zambian waters, and that it could not reproduce unassisted in ponds, St Joseph's Mission in the Copperbelt has self reproducing populations of mirror carp in their ponds. These carp lay eggs on aquatic vegetation and can sustain themselves in polyculture with tilapia. Furthermore, the common carp has many reproductive traits in common with the local Labeo altivelis, such as spawning migrations and adhesive egg deposition on the substrate. Therefore common carp could be capable of establishing itself in Zambia.
The attitudes on Chinese carp in Zambia are derived from experience with the common carp that was introduced in the early 1980's. There was an initial acclimation period of about 3–5 years before local people became accustomed to eating common carp. Nearly all of the fish farmers interviewed, e.g. F.Flynn, Kafue Fish Farms, B. Kumar, Nchanga Fish Farms, and the Department of Fisheries reported a market demand for large fish that could be met by supplying Chinese carps. In addition F.Flynn and Father Tony of St Joseph Mission expressed an interest in introducing grass carp into production ponds to improve water quality and remove some aquatic vegetation. It appears that through the assistance of Dr A. Woynarovich, NORAD, grass carp are planned to be introduced to Kafue Fish Farms from South Africa. Dr Soma of Mwekera hatchery is currently planning the purchase of 100 silver and bighead carp and between 50 and 100 grass carp from Japan or Egypt (pers. comm.). The one farm with experience breeding grass carps in Zambia, Mazabuku Fish Farm, owned by W.F.R. Lublinkhoff, is not considering using this species because of past failures (Mr Mimnoss Miyoba, hatchery technician, pers. comm.). The Department of Fisheries sees very little environmental risks from the introduction of grass carp in Zambia and views their introduction as inevitable (Victor Mulenga, pers. comm.).
Another stated rationale for the introduction of Chinese carps is that, as an exotic species it will command a higher market price than native species (Mr Mudenda, Director, Department of Fisheries, pers. comm.). All farmers giving selling prices of fish stated that common carp sold for around 1600K/kg while tilapia sold for about 800 – 1000K/kg (Table 4). The current price of carp limits its availability to the higher income sector of Zambia. One reason for the high price of carp at present is the limited supply of carp. It is unclear whether these prices would be maintained as more carp become available on the market.
The introduction of Chinese carps is seen as an activity for the commercial scale fish farmers in Zambia. This sector will be most able to manage ponds, artificial spawning procedures, marketing and distribution of new species such as Chines carps. Two other sectors of fish farmers, the mid level farmers that may grow a mix of native and exotic fish, and the village or small scale growers that concentrate on easily managed local species such as tilapia and catfish, would not be specifically targeted for Chinese carp production or grow-out.
Culture of Labeo altivelis, a commercially valuable local cyprinid is planned to mitigate reduced numbers of this fish through loss of spawning habitat. Artificial reproduction of this species has been achieved previously in Kenya and it has a favourable growth rate. However, the level of interest in this species seems to be low or non-existent in light of plans to culture exotic carps.
Selected aquaculture and fishery activities dealing primarily with tilapia and carps are presented in Table 2. Commercial fish farming of tilapia is established in the Banket Agricultural area and surrounding Lake Kariba. Some of these commercial producers cannot meet demand for tilapia and supply fish for export. However, others in the Lake Kariba area cannot command a price sufficient to make much profit. The farmers in the Banket region primarily culture nile tilapia, O. niloticus, whereas the Lake kariba Fisheries Research Institute is discouraging the use of this species in Lake Kariba area in favour of local tilapia. Local species of tilapia were tried in Kariba Bream Farm, but given up in favour of nile tilapia which doubled production. Farmed fish have a difficult time competing with wild caught fish in the vicinity of Lake Kariba (Table 4). Adverse attitudes on catfish, similar to those felt in Zambia, also exist in some areas of Zimbabwe.
Following a severe drought in 1991 and 1992, many of the reservoirs dried out in the country. A plan was implemented to restock these reservoirs with fish from those areas that maintained their water supply. A plan was also proposed (Keith Nicholson, pers. comm.) to restock with specific strains of improved or selected tilapia spp. One suggestion was that O. niloticus should be stocked. Presently, the restocking programme is simply catching small fish from existing water bodies and transporting them to selected reservoirs.
Two species of Chinese carp, bighead and silver, were introduced into the Freshnet Fish Farms along Lake Kariba. There has been limited use of these species, as silver carp is the only one being reproduced. Silver carp had problems with hatching rate and the brood stock suffered 100% mortality following spawning. Common carp were introduced in the 1920's (Welcomme 1988) and are prevalent in fish farms in the country. However, none are thought to be in Lake Kariba.
Common carp continue to be stocked occasionally by government agencies. These fish are reproducing in the reservoirs, but are not extremely prolific and not thought to be spreading outside of the areas of their original introductions. The Department of Natural Parks and Wildlife concluded that common carp present no real threat to the aquatic environment in the country (Sophie Mutsekwa and Chris Nugent, pers. comm.). It should be noted that much of the aquatic environment suitable for fisheries in Zimbabwe is a result of modification of naturally dry areas with little permanent water by the construction of numerous reservoirs and impoundments.
There is a native cyprinid, Labeo altivelis, that supports a modest gill net fishery in the area of the inflow to Lake Kariba. This fishery lands 2,000 tonnes/yr with a value of 12,000,000 Z$ (6.4Z$/US$). This species shares some characteristics with common carp in that they migrate up rivers following the first rains and lay adhesive eggs on the substrate in shallow water. There is currently no work on this species, but a culture programme is planned (Dr Machena, pers. comm).
Although the experience with Chinese carps in the farms visited was generally poor, there is a desire to utilize grass carps to clean up pond vegetation. For example, Ron Evans of Rothman Fish Farm doubted that local people would accept carp as food, but wanted to import white amur (grass carp) to help control filamentous algae and other aquatic plants. Mr K. Nicholson of Kariba Bream Farm is reluctant to grow Chinese carp after observing the experience in the neighbouring Freshet Fish Farm, however, he would like grass carp to reduce aquatic weeds that hamper harvesting of ponds.
There is also a plan to introduce grass carp from South Africa or purchase from Freshnet Fish Farm to control aquatic vegetation in Chivero and Manyami Dams (Dr Machena, Kariba Fisheries Research Institute, Ms Sophie Mutsekwa, Dept. of National Parks, pers. comm.). Lake Kariba Fisheries Research Institute is not aware of any adverse effects from the use of grass carp in South Africa and wishes to conduct trials on its effectiveness at removing the aquatic macrophyte Lagarosiphon iliciofolius from reservoirs. The Department of National Parks is planning to produce triploid grass carp for stocking into the above reservoirs to reduce risk of establishing self reproducing populations of grass carp. Local species, such as T. rendalli, are not expected to be able to control aquatic plants that are presenting problems.
Generally, most of those people interviewed thought that Chinese carps would be accepted in the local market. It was felt that there is a market for fish of about one kilogram, but not much larger. Chris Nugent (AGRITEX) stated that species of carp that continue to grow during periods of the year that are too cold for tilapia culture may be desirable for culture in the higher elevations of the country.
Inland aquaculture activities in the country are limited at present due to political and economic instability in the recent past and a severe drought during 1991 – 1992 (Table 3). Many of the large reservoirs support small scale fisheries, however fish farming has only limited participation. In Gaza Province, 100 licensed fishermen and probably 100–200 unregistered fishermen operate on the Massinger Reservoir; downstream at the Macarratene Reservoir the fishery is smaller, but active. Fish farming in Gaza is undertaken by only 4 or 5 private fish farms that exist in conjunction with traditional agriculture. No family farms are operating in the area. In the Manica Province no fish farms were reported, however reservoir such as Chicamba supported capture fisheries of tilapia and black bass. It should be noted that there were no farmers dedicated solely to fish farming in the Provinces visited.
Currently the Department of Fish Culture operates the Chizizzira Hatchery in the Manica Province near Choimoio (Figure 1) for stocking common carp and tilapia O. niloticus and T. rendalli. The growout ponds have a problem with infusion of wild O. mossambicus and the loss of pure species through hybridization. There are hatchery facilities planned for Mapapa and Lionde near Chokwe (Figure 1) in Gaza Province. The Umbeluzi facility near Boane in Maputo Province (Figure 1) is in poor condition and suffers problems with water infiltration from nearby rivers and irrigation. The status of which department within the Ministry of Agriculture will operate the Umbeluzi farm is unclear and financial resources are needed for its continued existence. The major tilapia species stocked by the Department is O. niloticus. Some farmers attempted to use local O. mossambicus, but switched to O. niloticus because of poor growth.
A marine shrimp project is ongoing at the Costa del Sol, Maputo, managed by FAO and the Secretary of State of Fisheries. This project which has focused primarily on research is nearing termination. There are plans to expand to pilot scale and eventually to commercial scale farms.
Inland fisheries provide protein to the inland regions of the provinces visited. However, some marine fish are also being sold frozen in Gaza Province. Generally, the marine species are more expensive and have limited distribution due to spoilage. Inland fishes also have transportation and spoilage problems as roads are in state of disrepair following the war. To avoid some of the problems with spoilage of fresh fish, salted, smoked, dried, and cooked fish are transported and sold in many markets. Cold storage is almost non-existent, however one vendor maintained a freezer and sold frozen marine fish in Chokwe.
Common carp is currently produced for stocking and dispersal to interested farmers free of charge by the Department of Fish Culture at their Chizizzira and formerly at their Umbeluzi facilities. Original introduction of common carp was probably from South Africa. There are plans to continue production of common carp at the Department's Mapapa farm near Chokwe.
Contrary to the report of Marshall (1993), common carp appear to be established in many of the rivers within both Manica and Gaza Provinces. How prolific they are in these rivers is unclear. The Chizzizira hatchery allows natural spawning of carp in ponds with tilapia species indicating that common carp can reproduce in the presence of some tilapia. Department of Fish Culture staff at the Chizizzira Facility reported common carp in the canal and river that supplies the hatchery. Local fishermen in the Chokwe and Massinger areas report common carp in rivers originating in South Africa and the canals of the irrigation scheme. Fishermen report peak catches of common carp during the rainy season when South Africa increases the flow in the Oliphants and Limpopo Rivers for flood control. Therefore, Gaza province may also be getting regular infusions of common carp.
Introduction of approximately 4000 Chinese carp fry occurred in October 1991 from Cuba. Chinese carps had been introduced to Cuba from the former Soviet Union during the mid 1960's. Currently approximately 1500 bighead, grass and silver carps are being maintained at Department of Fish Culture's facilities at Umbeluzi in Maputo Province and at Mapapa facility in Gaza Province. These fish appear in good condition and some may be sexually mature in the warm season (beginning in October) of 1993. There is a mild occurrence of Lernea spp. in silver carp at the Mapapa facility that may have originated from local water supply, as no infestations were observed in the group of fish held at Umbeluzi. The Lernea spp. copepods occur throughout the waters of southern Africa and infect a wide variety of cichlid and cyprinid fishes.
There is a native carp, Labeo rosa, from the Limpopo - Oliphants Rivers that is currently being held at the Department of Fish Culture's Mapapa facility. Plans for this fish are unclear at present although it appears that artificial breeding and growth trials will be attempted along with breeding of the Chinese carps.
In addition to the interest of the Department of Fish Culture in using Chinese carps that prompted this consultation, there is some desire by the few local fish farmers interviewed to grow Chinese carp in polyculture. Father Maglhaes of the Old Mission in Chokwe specifically wants grass carp to help clear his ponds of aquatic macrophytes. Again, it is generally felt that local people will accept Chinese carp because common carp and Labeo rosa are prevalent and accepted. However, several farmers stated that the carp has too many bones and is too oily. The market would appear to be for fish of about 1kg because larger fish would be difficult to process. It should be noted that the local fishermen and farmers do not distinguish between the native species of carp and common carp. However silver and bighead carps appear morphologically different from common carp and silver carp is said to be less oily that other carps.
There is a high level of interest in growing Chinese carp from the senior Vietnamese fish culturists employed by the Department of Fish Culture. The Department is also considering utilizing Chinese carps in other irrigation schemes such as the one in Xai xai, Gaza Province and for stocking reservoirs in the Manica and Maputo Provinces.
The grass carp has been proposed as a means to help control aquatic vegetation in the SIREMO Irrigation Scheme, an extensive irrigation programme near Chokwe in Gaza Province. This irrigation facility diverts water from the Limpopo River below the confluence of the Oliphants River via two main canals. There are numerous smaller feeder canals (approximately 300 ha total) that supply water to approximately 30,000 ha of land.
In 1980, land within the scheme was distributed to families and the private sector. After some initial attempts at cooperatives and state controlled land allotment, families were awarded 1 – 2 ha and the private sector was awarded 3 – 30 ha. Several large private companies farm from 1500 to 2600 ha of land within the scheme. Participants in the scheme pay a flat rate for their water, determined by how much land they have. The current rate is 150,000mt/ha/yr, although some participants are delinquent with their payments. Family farmers may be awarded, and therefore charged for, 2ha of land, but most family farmers only work .5 – 1ha. Thus there is unutilized land within the scheme.
Cotton, rice, corn, beans, and sorghum are the priority crops within the scheme. At present cattle are also grazing within the scheme, but this is due to pressures associated with the recent conflict and displaced people. Portions of the scheme (approximately 8,000 ha) have high soil salinity and are unsuitable for agriculture.
Clearing the canals of aquatic vegetation is a major activity of SIREMO. The mission observed several aquatic grasses and weeds in the canals (Table 6). Many of the smaller feeder canals of approximately 5m width were extremely congested with miscellaneous grasses. Precise identification of these plants is being undertaken by the Department of Fish Culture.
Also within the scheme are drainage areas that collect standing water. Water hyacinth was observed in some of these sinks, but this plant was not seen in the canals. Water lilies, Nymphae spp. were also observed in the drainage areas, but were nearly absent from the canals.
Marshall (1993) presented data that indicated that the use of grass carp was a cost-effective means of controlling aquatic vegetation. It is expected that grass carp would help alleviate the severe weed problems within the SIREMO irrigation canals and may help partially control vegetation in the drainage sinks. However, it is not clear that the use of grass carp in the canals will increase food availability from fishing as Marshall stated. Current regulations prohibit fishing in the irrigation canals to prevent damage to the canals and levees. However, this regulation is difficult to enforce and fishing was observed in the scheme. Fishing is permitted in the drainage areas and is taking place at an unknown level of activity.
Information gathered during the 3 week consultancy was used to evaluate the feasibility of a pilot scale project on the use of Chinese carps in Mozambique. In appreciation of the facts that the use of introduced species can have tremendous benefits as well as adverse impacts, an effort was made to apply a logical framework in order to evaluate the introduction. The framework to be used in this instance is the ICES/EIFAC Code. This Code recommends the use of a decision tree and rating system from Kohler and Stanley (1984) (Figure 2) that is one means of evaluating a proposed introduction.
Two reasons were stated in the Project Proposal as justifying the use of Chinese carp in Mozambique: 1) to increase fish production from fish farms and from stocking reservoirs and 2) to help control aquatic vegetation in irrigation canals. Although these activities are complimentary the two are treated separately and are evaluated individually as justification for the proposed introduction.
The first level of review in the Code determines the validity of the proposed introduction. Question 1 of Decision Box 1 (Figure 2) asks “is the need valid and are no native species available that could serve the stated need”. The mission, SIREMO technicians, and Marshall (1993) perceived a need to control aquatic vegetation within irrigation canals. Local species that may control the vegetation such as Tilapia rendalli are presumably present in the canals and have not been effective in this regard. The proposed introduction appears to “probably” satisfy a valid need, not met by local species.
The grass carp is in no danger in its native range (Question 2, Figure 2)
With regards to adequate safeguards to guard against importation of disease (Question 3 Figure 2), the following must be considered. There was a preliminary screening of samples of the Chinese carp when they were first introduced in 1991. Specific examinations for the most important parasites of Chinese carps, namely the tape worm Botriocephalus acheilognathi, and the copepod ectoparasite, Lernae spp. were negative (Mr Boane, University of Eduardo Mondlane, pers. comm.). Infestations of tape worm would have proven fatal to the stocks of Chinese carp, however these fish appear healthy at present. Both of these parasites have been reported in southern African waters, therefore, the risk of introducing novel parasites is minimum. Treatment of these parasites are well known (Dr Woynarovich, Mr Boane, Mr Phan, pers. comm., Jhingran and Pullin 1985)
It should be stressed that the Code recommends that the original imported stocks, in this case, grass carp from Cuba, should not be stocked, but that F1 progeny should be used instead. Therefore adequate safeguards are “possible”.
The planned use of grass carp is in the SIREMO irrigation scheme with connections to the Limpopo River. Therefore, the introduction would not be in closed system (Question 4 Figure 2) and we proceed to the second level of review, the determination of acclimation potential. It is presumed that Chinese carp in general and grass carp in particular have such precise requirements for reproduction that they are unable to naturally reproduce outside of their native range in Asia. The following information is reported in Chilton and Muoneke (1993). Grass carp require large rivers and flood conditions to reproduce. Eggs are buoyant and must be kept in suspension by rapidly flowing rivers for between 20 and 40 hrs depending on water temperature. Flow rates needed to keep eggs in suspension were reported to be 0.2 – 0.6m/s. Larvae are capable of only vertical movement until the yolk sac is absorbed, which occurs at 3 – 4 days post hatch (Jhingran and Pullin 1985). In the event that grass carp did escape from the irrigation scheme and spawned during flood periods, their eggs and larvae would be washed into brackish lagoons or the Indian Ocean as Chokwe is approximately 60 km from the brackish water. Grass carp would not be able to pass upstream or into South African waters because of barriers at Macarretene and Massinger. Another factor which reduces the chance of grass carp establishing itself in the Chokwe region is that periodic droughts completely desiccate the Limpopo River downstream of the large reservoirs. Marshall (1993) presented information that indicated Chinese carp would not be able to reproduce unassisted in Mozambique, because of specific breeding requirements, heavy predation from local fishes, and periodic flooding and droughts. Personal communications with fishery biologists with experience in Africa and aquaculture (R. Welcomme and T. Petr, FAO Rome) also indicated that the probability of self-sustaining populations of Chinese carps in southern Africa is very low.
Therefore, grass carp would “probably” be unable to establish itself in the range of habitats planned for introduction (Question 5 Figure 2) and one would approve the introduction for the purpose of aquatic vegetation control.
In order to assess better the validity of the proposed introduction of Chinese carp for increased fish production, Question 1 was rephrased and broken down into two subsections: 1a. “is the need valid and are the stated methods the most suitable to achieve the objectives?,” and 1b. “are no native species available that could serve the stated need?” There is certainly a need to increase production of fish in Mozambique, however, it is not at all certain that this need can be met by farming Chinese carp or from stocking reservoirs with Chinese carp. Therefore, evaluation of question 1a focuses specifically on the suitability of Chinese carp farming and restocking as a means to increase fish production.
Fish farming is currently a low level activity in Mozambique, practised by only a few commercial agriculturist and not practised by any family farmers. Therefore, only a few farmers would utilize the fish initially, and the sector would have to expand significantly to see much utilization of the Chinese carps. Experience in other areas has shown that where land, water, labour, and extension services are available, fish farming has in fact expanded. In parts of Mozambique, such as SIREMO Irrigation Scheme, land and water are available, but extension programmes in fish culture are only now beginning and it is unknown if extension will be available for extensive low-level family fish farmers.
Families currently practising traditional agriculture in the SIREMO Irrigation Scheme farm only.5 to 1 ha of their allotted 2 ha parcels. This may be due to the fact that there are peak demands on labour associated with preparation for planting and harvesting that limit the area that can be cultivated. During non-peak periods, traditional farmers would have minimal labour demands and may have time to prepare and maintain fish ponds (A. Andreasson, ALCOM, pers. comm.). However, it remains unknown whether small scale or family farmers in Mozambique would want to spend the effort and money to build and maintain fish ponds.
Farmed fish would need to compete in the market with capture fisheries in Mozambique. Prices of fresh fish ranged from approximately 1600 – 2500mt/kg, whereas processed fish ranged from 2500 to 5000mt/kg. Experience from Lake Kariba, Zimbabwe (Table 4) has shown that farmed fish are more expensive than wild caught. Therefore, it is doubtful whether many of the rural people would be able to afford farmed Chinese carp, even if commercial farmers began producing. An unskilled labourer working a field would earn about 2500mt/day (Dr Merle Bowen, University of Illinois pers. comm.) or only enough for one to two kg of fish at current market prices for wild caught fish. There may be a market for export of inland fishes, but this was not determined.
Marshall (1993) stated that the culture of Chinese carps would benefit farmers in the country because of the shortage of animal manure to fertilize ponds and shortages of other inputs. However, the current consultancy found that the few fish ponds in Mozambique all operate in conjunction with animal and crop production. Therefore, manure and other agricultural by-products are available and indeed are already in use in tilapia culture. It may be that Chinese carps would utilize these resources more efficiently than the tilapia and common carp. It should be noted that although Chinese carp polyculture is widely practised throughout the world, the experiences of Freshnet Farms in Zimbabwe, the Department of Fisheries in Chilanga, and the Muybuyu Fish Farm in Zambia reveal that Chinese carp are not as easy to maintain in southern Africa as tilapia.
With regards to the stocking of reservoirs with Chinese carps to increase fish production, there are simply no data to indicate that the fisheries in these reservoirs need restocking. Indeed, there is little information at all on the inland fishery resources of Mozambique. The reservoirs visited during the consultancy had active tilapia and tiger fish fisheries, that may be impacted by the continued stocking of Chinese carps. An obvious alternative to stocking Chinese carp would be to consider stocking native tilapia (see below on use of indigenous species), if future surveys indicate stocking is needed at all.
Therefore, the use of Chinese carp in culture systems to increase food production is questionable (Don't know of Figure 2), and success of increasing production from stocking Chinese carp in reservoirs is “unlikely” (Figure 2). The use of Chinese carp is especially suspect in light of other alternatives, such as improved management of capture fisheries, improved transport and fish processing of wild caught fish, increase availability of fishing gear and boats, and utilization of native species (1b below). According to the decision box for question 1a, there is good reason at this stage to reject the introduction of Chinese carp for increased fish production. However, the decision process can be continued to question 1b “are no native species available that could serve the same need?”
As to the native species available for fish farming (1b), several species of native and naturalized tilapia are readily available (Table 3). Tilapia culture has spread globally and in areas where Chinese carp have been farmed for centuries. The reasons for this are that tilapia is an easily cultured and marketable group of fish. In addition there is at least one native species of cyprinid, Labeo rosa, that may be a suitable species for fish culture.
Based on these observations, the answers to question 1b in Decision Box 1 (Figure 2) is “No” or “Unlikely”. Therefore, introducing Chinese carp for increased food production from either fish farming or stocking is judged to be invalid and the introduction of Chinese carp is also rejected on the basis that practical alternatives exist.
Based on an application of the ICES/EIFAC Code of Practice, it is recommended to proceed with a pilot scale project on the use of grass carp as a means to control irrigation canal vegetation within the SIREMO Irrigation Scheme (Figure 1). Specific sections of small feeder canals should be partitioned and stocked with progeny of the grass carp currently held at Mapapa Hatchery. Other sections should be stocked with local species that may also control aquatic vegetation such as T. rendalli. Quantitative data should be recorded on numbers of fish stocked, size at stocking, growth rates, survival rates, and efficiency of weed control.
In light of the valuable aquatic resources in Mozambique and surrounding countries and the potential for adverse impacts from introductions of exotic fishes, it is advised that the use of grass carp be restricted to the SIREMO Irrigation Scheme and the associated Mapapa Hatchery in Chokwe. When the status of the Umbeluzi station is decided it may be appropriate to use this facility for disease diagnostic training. Although the use of grass carp is considered for other irrigation schemes, such as in Xai xai, these areas were not evaluated by the mission and it is recommended to concentrate on the Chokwe area to adequately assess the use of grass carp. To reiterate the recommendation of Marshall, under no circumstances should Chinese carp or any other exotic fishes be allowed in the catchment regions of Lake Niassa.
Many cyprinids have similar culture and reproductive requirements. Therefore, it is recommended that the Department of Fish Culture, Mozambique continue to work on the culture of silver and bighead carps, and especially on the native Labeo rosa. The culture of the planktivorous silver and bighead carps will help improve and stabilize water quality for the grass carp broodstock when all three species are grown in polyculture. With the projected stabilization of Mozambique, the fish farming sector may experience an increase in activity. In this case, experience gained from the Mapapa Hatchery may be applicable in the future.
Fish culture extension programmes are currently underway in Manica Province for District Directors of Agriculture through the assistance of GTZ and ALCOM. It is recommended to continue this activity, to follow its progress in Manica and explore means to arrange extension activities in Gaza Province in regards to expanding the fish farming sector if the extension activities are successful at promoting family aquaculture in Manica.
Throughout the consultation the mission observed a lack of trained aquatic disease personnel and it is recommended that increased activity in this field be pursued. Although the Chinese carp in Mozambique appear to be healthy, a specialist in fish diseases should be commissioned to examine the remaining stocks of Chinese carp. The specialist should also supervise treatment of any pathogens or parasites and provide for periodic inspections of the fish fauna of the irrigation canals at Chokwe. Due to the tremendous interest in exotic fishes in the Region, consideration should be given to a regional training course in basic aquatic disease prevention, diagnosis, treatment and quarantine.
The government body currently responsible for inland aquaculture is the Department of Fish Culture under the Ministry of Agriculture. However, coastal aquaculture, marine and inland fisheries, and the large lakes, Niassa and Cohora Bassa, are under the jurisdiction of the Secretary of State of Fisheries. This isolation of inland aquaculture from other fishery activities prevents coordination and the establishing of consistent priorities for the aquatic sector. It is recommended to consider a re-organization of this situation possibly through a coordinating body composed of both aquaculturists and fishery biologist and from both marine and inland backgrounds.
Once coordinated activities for the aquaculture and inland fisheries sector are possible, it is recommended to create a national work plan and establish priorities for development, research, conservation and extension and training.
The aquatic resources and inland fisheries of Mozambique are poorly documented and poorly understood at present. With the stabilization of the country and following guidelines established in a national work plan, it is recommended to instigate surveys to identify trends in inland fishing, areas of rich aquatic resources, areas of special conservation value or preserves, and areas suitable for modification or development. There is an IUCN project to document coastal marine resources in the country (Mr A. Massinga, pers. comm.) and a similar project should be developed for Mozambique's inland resources which may be more endemic and more endangered.
It is expected that the agriculture and fishery sectors in Mozambique will evolve in unforseen ways with the stabilization of the political and financial situation in the country. Therefore, socio-economic studies such as are already planned by ALCOM should be undertaken. These studies should address, inter alia, specific questions of:
These questions can be addressed by field surveys in provinces where the expansion of fishery production is planned. Experience from other southern African countries will also be useful in a priori evaluation of the use of exotic fishes, such as Chinese carps. For example, in Zambia carp were initially not liked, but presently they are accepted and command a high price. It will be instructive to follow the trend in the price of carp in Zambia as more fish become available. It will also be beneficial to follow the technical progress of Chinese carp culture in Zambia and Zimbabwe.
I wish to thank ALCOM for facilitating this consultancy. The cooperation and assistance provided by Ms Maria do Carmo Carrilho (Department of Fish Culture, Mozambique) and Mr Boyd Haight (ALCOM) are especially appreciated.
Chilton, E.W. and M.I. Muoneke. 1992. Biology and management of grass carp (Ctenopharyngodon idella, Cyprinidae) for vegetation control: a North American perspective. Reviews in Fish Biology and Fisheries 2: 283–320.
de longh, H.H. and J.C.J. Van Zon. 1993. Assessment of impact of the introduction of exotic fish species in north-east Thailand. Aquaculture and Fisheries Management 24: 279–289.
Jhingran, V.G. and R.S.V. Pullin. 1985. A hatchery manual for the common, Chinese and Indian major carps. ICLARM Studies and Reviews. Asian Development Bank and ICLARM, Manila, Philippines.
Kohler, C.C. and J.G. Stanley. 1984. A suggested protocol for evaluating proposed exotic fish introduction in the United States. Pages 387–406 in W.R. Courtenay and J.R. Stauffer, eds. Distribution, Biology and Management of Exotic Fishes. John Hopkins University Press, Baltimore, MD.
Marshall, B.E. 1993. Environmental impact study on the introduction of Chinese carps into Mozambique. Consultancy Report, ALCOM, Harare, Zimbabwe.
Turner, G.E. (editor). 1988. Codes of Practice and Manual of Procedures for Consideration of Introductions and Transfers of Marine and Freshwater Organisms. EIFAC Occasional Paper No. 23. European Inland Fisheries Advisory Commission, FAO, Rome, Italy.
Thys van den Audenaerde, D.F.E. 1992. The introductions of aquatic species into Zambian waters, and their importance for aquaculture and fisheries. Consultancy Report, ALCOM, Harare, Zimbabwe.
Vanden Bossche, J.-P. and G.M. Bernacseck. 1990. Source book for the inland fishery resources of Africa. Vol. 1. CIFA Technical Paper 18/1. FAO, Rome, Italy.
Welcomme, R.L. 1988. International introductions of inland aquatic species. FAO Fisheries Technical Parer No. 294. Food and Agriculture Organization, Rome, Italy.
Wynn, F. 1992. Controlling aquatic vegetation with triploid grass carp. World Aquaculture 23: 36–37.