Divisional Scientific Officer, Ministry of Fisheries
Port Louis, Mauritius
1 Presently FAO Scientific Officer, South West Indian Ocean Project, Victoria, Mahé, Seychelles
Coastal and brackish water aquaculture, its problems and possibilities of development have been studied in nine countries of the African region: Ivory Coast, Benin, Egypt, Ghana, Kenya, Madagascar, Mauritius, Nigeria and Tunisia.
The geomorphology of the coastal region is briefly described, including coastal lagoons (Madagascar, Ivory Coast, Benin, Ghana and Nigeria), coastal lakes (Egypt and Tunisia), mangrove swamps (Madagascar, Kenya and Nigeria) and coastal areas sheltered by coral barrier reefs (Mauritius).
Practices of extensive aquaculture are discussed and assessed, including: (i) Anadromous migration to coastal lakes and lagoons - this should be facilitated, the depth of the openings being however limited in order to prevent excessive leaching of nutrients to the sea; (ii) Acadjas - where wood is available, their use is encouraged within specified guidelines; (iii) Barachois - difficulties of management are stressed and (iv) Fish introduction and stocking-guidelines are suggested to avoid undesirable effects.
In semi-intensive aquaculture, problems include competition for fish seed in howash farms (Egypt) and for forestry resources and capture fisheries in mangrove swamps.
Intensive aquaculture in ponds, in cages and in netting enclosures is discussed, including problems of seeding, mortality, feeds and technical development, on the basis mainly of the experience gained in Ivory Coast.
Finally, general problems of aquaculture are discussed, including criteria for species selection and the dangers of irresponsible introduction of exotic species, problems of fish seed production for intensive and semi-intensive aquaculture, the use of fertilizers and feeds, the lack of technical and extension personnel, problems of pollution, the availability of finance and problems of marketing.
1.1.1 The production of fish through aquaculture is significant today only in South-East Asia. In many countries of Africa, however, there is a tradition of extensive aquaculture activities. Little attention has been given to these activities, as the development of capture fisheries in both the sea and the lakes and rivers took precedence in planning. The demand for fish throughout Africa has continued expanding, as populations increase at rates varying between 2.5 and 3%, as urbanization increases the dependence of people on external food sources, and as improved communications open new markets. In most areas, capture fisheries can now be developed little further, and many countries in Africa are having to make up deficite in production through imports which constitute a heavy drain in foreign exchange. For freshwater aquaculture, prime agricultural land is often required, as well as water which is also needed for crop production and for human and industrial development. Attention is now being focused on the coastal environment, therefore, as saline lands and brackish waters have no use for agriculture, but can well be used for the production of fish.
1.1.2 In planning aquaculture development, the temptation of introducing high level technologies as an easy solution to increasing production must be resisted, at least in the short-term. This type of technology requires heavy inputs in scientific knowledge, in extension services, in equipment and in energy which are often more needed elsewhere. It often requires long study to adapt techniques to a specific environment and it is not necessarily the most cost-effective solution. While research into such technologies is necessary for long-term development, much can be learned from traditional methods. These can often be easily improved and less resistance is encountered from rural people who are reluctant to drastically change their ways.
1.1.3 A study tour was made of selected coastal countries in Africa including Mauritius, Madagascar, Kenya, Ivory Coast, Ghana, Nigeria, Egypt and Tunisia. Due to unforeseen circumstances, Benin could not be visited although it has been included in the case studies as it provides examples of aquaculture practices available nowhere else. A literature review provided historical and background information.
1.1.4 Aquaculture, in the context of this paper, will be taken in its widest sense. The dividing line with capture fisheries is sometimes very tenuous, but any increase in production from an area through human intervention beyond that of merely harvesting the fish will be considered as aquaculture. Examples of the type of intervention envisaged could include facilitating seeding from natural sources, increasing the species diversity by the introduction of exotic species, provision of shelter from predation for young fish, improvement of primary productivity by provision of a substrate or by fertilization, and finally, feeding and other intensive aquaculture practices.
1.1.5 The criteria proposed by Ravagnan (1978) will be adopted to classify the forms of aquaculture. Accordingly, aquaculture is intensive when all the nutritional needs of a fish are met from external sources, semi-intensive when part of the nutritional requirements come from the environment, and extensive when no fertilization or feed is used to supplement natural production. Division of forms of aquaculture on the basis of seeding or production per unit of surface or volume would be arbitrary and not necessiraly connected with the scale of intervention applied or the technology involved.
1.2.1 Not all coastlines provide the necessary conditions for aquaculture as some protection must be afforded from the action of the open sea. Along the West African coast, between Ivory Coast and Central Nigeria, and on the East Coast of Madagascar, strings of lagoons have been formed between the shore and sand banks lying parallel to the coast. These lagoons are only a few hundred metres wide in many places, but elsewhere widen into lakes, which may be tens of kilometers across. Most of the rivers along these coasts open into these lagoons, and in periods of high rainfall, the salinity in a whole lagoon may fall to nearly zero. In the dry season, however, sea water entering through channels and by percolation through sand banks may raise the salinity, at least on the seaward side of the lagoon, to values in excess of 25 %. In consequence, the term brackish water species is taken to mean any species which can tolerate these salinity fluctuations, as opposed to freshwater and marine species which have more limited tolerance to salinity changes.
1.2.2 In the delta region of the Nile, and along the Egyptian coast which is mainly sandy, and similarly along the Tunisian coast, depressions have led to the formation of extensive lakes. The Egyptian lakes are for the most part very shallow, but Bizerte lake in Tunisia reaches depths of over 6 m. These lakes also show very wide variations in salinity. Many of the rivers carry a substantial amount of salt and with the very high evaporation during the summer months, the tendency is for salinities to be fairly high. Some lakes become considerably more saline than the sea and values over 70 % have been recorded. The species cultured in these regions, therefore, are generally closer to the marine than to the freshwater faune. Apart from extensive aquaculture activities which are traditional there, these lakes and lagoons are suitable for semi-intensive and intensive aquaculture in ponds, enclosures and cages. The very small tidal range however makes the two latter systems preferable.
1.2.3 In Mauritius, a particular situation is caused by the presence of a fringing coral barrier reef. This forms a sheltered and fairly shallow lagoon in and out of which fish move freely. In such an area, aquaculture can only be carried out in man-made enclosures.
1.2.4 Apart from naturally occurring water areas, low lying flat lands may be used for aquaculture development. Along sea coasts, tidal fluctuations can be used for filling and draining ponds. Mangrove swamps along the coast of Kenya and along the Northern and Western coast of Madagascar provide ideal conditions, with tides sometimes in excess of 4 m height. In Nigeria, east of the Niger delta and more particularly along the Mediterranean coasts of Egypt and Tunisia, the small tidal range is a handicap which can be overcome by using pumps, although this increases costs substantially.
2.1.1 Many species of fish and crustacean migrate as juveniles from the sea into brackish and fresh water (anadromous migration). Among them are found many mullets (mugilidae), milkfish (Chanidae), Elops spp., Chrysophrys auratus, Dicentrarchus labrax, freshwater eels (Anguilla anguilla, A. mauritianus) many penaeid shrimps, etc. Some of these species may spend most of their adult life in fresh water, only returning to the sea to breed. Other marine fish (e.g. Siganidae, Carangidae) move into brackish water areas for feeding, but will not stay there unless trapped. This type of migration provides much of the seeding of coastal lakes and lagoons where the diversity of species breeding in fresh or brackish water is insufficient to fill all ecological niches. It should also be noted that these anadromous species are also often preferred by consumers to the true fresh and brackish water species.
2.1.2 Nearly all the coastal lagoons in the countries under study have some connection to the sea. These connections are either directly to the sea or in some cases (e.g., the Keta Lagoon in Ghana and the Pangalanes in Madagascar, may be into the estuaries of rivers, usually in the tidal zone. Often, the connection is only open seasonally when the influx of freshwater raises the level of the lagoons sufficiently for the water to flow over a sill (e.g. Bizerte), or to break through sand dunes, making a passage which is afterwards closed by sand shifted by coastwise currents (e.g. Keta Lagoon, Ghana).
2.1.3 In some cases the coastal dunes have been strengthened and stabilized by the construction of railroads or roads (Pangalanes-Est - Madagascar), preventing the opening of connections with the sea. The result has been, in the high rainfall areas, to decrease the salinity and to cause wide fluctuations in lagoon water levels. The flood level of the Keta Lagoon since its closure can reach 2 m above sea datum, while during the dry season evaporation can lower the water to 0.3 m below sea level, reducing the area of the lagoon by half.
2.1.4 Permanent closure of a lagoon can have serious affects on its fisheries. The Keta Lagoon (Ghana), which was considered very productive, particularly in valuable species such as shrimps and mullets, now produce virtually only cichlids. The seeding through the outlet to the Angaw Lagoon to the Volta River is only sufficient to seed the latter lagoon. In the Pangalanes-Est, the combined effect of insufficient seeding and selective fishing methods has shifted the stock composition to the point where by 1968 52 % of the species caught were carnivorous compared to a normal 20–30 % (Moulherat and Vincke, 1968).
2.1.5 The anadromous migration of young fish, followed by a catadromous migration of adults has, in many areas, formed the basis for a fishery. Stationary traps are made of wooden stakes (Madagascar, vila), netting (Egypt) or, more recently, wire mesh (Tunisia, bordigues), placed in the access channels between the lagoon and the sea. The meshes of these traps allow the passage of fingerlings, but retain the larger fish. In Egypt, the fish (mainly mullet) are allowed to jump over the vertical netting barrier, but are then caught in a net stretched horizontally above the surface of the water between stakes behind the barrier. In Tunisia, where the netting barrier is too high to jump, the fish are channelled into a capture chamber from which they cannot escape. In Madagascar, the fish are caught with nets in a open capture chamber, the fishermen remaining constantly on watch during the tidal phases when migrations are known to occur. In some cases, the traps are built facing both up and down-stream, so that adult fish migrating into freshwater are also caught. It has been suggested (Sivalingam, pers.comm. 1976) that the mesh size of the netting in the bordigues could be increased in order to allow the access of young fish as well as fry into the lakes. This, together with wintering facilities for undersized fish, could significantly increase production in the Tunisian lakes.
2.1.6 In the Pangalanes-Est (Madagascar) the combined effect of closure of the direct connections between the lagoon and the sea (1900, Inangy vinany closed; 1929, Andavakamenarana vinany closed finally) and over-effective use of the “vila” had led to the collapse of the fishery of the mullet Liza macrolepis. It has been reported that the catch of mullet in 1900 amounted to 72 000 fish. By 1960, the catch had dropped to about 15 000 fish, and in 1967 only 3 000 fish were caught although the fishing effort had remained constant (Moulherat and Vincke, 1968). It is thought that the whole reproductive stock of this species lives in the Pangalanes, and that too few adults reached the sea breeding grounds to ensure survival of the stock. The predominance of predators in the Pangalanes may have further reduced survival of fingerlings.
2.1.7 It has also been reported that fishermen from the Pangalanes had already, prior to 1910, noted the reduction in the catch of mullet, and ascribed it to the closure of the vinany. In lake Tampolo - Fenérive, slightly to the North of the Pangalanes, apart from the annual overflow into the sea, fishermen open small vinany into the sea every year (Kiener, 1960) and the species diversity in the lake is far wider than that of the Pangalanes. Kiener reports that the catch of fishermen can be multiplied by ten following the opening of vinany. This may, however, be partly due to adult fish migrating into the lake from the sea.
2.1.8 Negative effects on the opening of passages from coastal lagoon into the sea are reported from two areas, Ivory Coast and Benin, where harbour developments have led to the widening and deepening of outlets to the sea. In Benin, the production of fish from Lake Nokoué and Porto Novo Lagoon have dropped from 15 420 t in 1969, prior to the opening of the deepwater channel, to 9 300 t in 1964 and 5 600 t in 1969 (Welcomme, 1971). In the Ebrié Lagoon, Ivory Coast, a similar drop in production is reported following the opening of the Vridi Canal. Between 1964 and 1975, however, the number of beach seines and ring nets increased by 360 % (Verdeaux, 1979), the dimensions of the nets also doubling or tripling while the mesh size was reduced in the same proportion. It could be argued, therefore, that the reduction in total yield was due to heavy overfishing.
2.1.9 This situation does not hold for lake Nokoué - Porto Novo fishery, as, in 1970 alone, 20% of the fishermen of this area emigrated to Nigeria and elsewhere (Welcomme, 1971). A study of the hydrological conditions in these lagoons carried out by the CTFT (Centre Technique Forestier Tropical) between 1963 and 1965 provides conflicting information. Primary productivity was high in 1963, with peaks of well over 1 000 mg C/m3/hr and an average of 260 mg, but did not vary significantly between 1964 and 1965. Paradoxically, the periods of highest productivity corresponded with those of high salinity (i.e. of low influx of freshwater) as the sediments carried by the rivers feeding the lagoons lowered productivity by reducing light penetration. Salt also helps to flocculate clay in colloidal suspension, leading to clearer waters, so that production is higher at periods when salinity is high. When comparing the productivity from different areas of these lakes, the highest values are found near the river inlets, while the lowest values are near the channel to the sea. This would tend to indicate that the increased flushing of the lagoon, caused by the enlarged opening to the sea has resulted in the loss of nutrients and perhaps also of plankton to the sea, which might partly explain the reduced catches.
2.1.10 In conclusion, therefore, some care should be exercised in attempting to enrich an area of lagoon by increasing the number and size of outlets to the sea. As long as these outlets are small enough to allow the passage of fish without greatly perturbing the hydrology of the lagoon, the effect is undoubtedly beneficial. The volume of water flow should not be increased to a level where nutrients are leached out of the system. Conversely, the fluctuations in the hydrology caused by closing a lagoon also bears negative consequences. Channels to the sea should preferably have a sill fairly close to high-water level, allowing the entry of sea water during high tides and allowing flood water to flow out, but preventing a constant leaching of nutrients.
2.1.11 Fishing by means of bordigues and vila represent a monopolistic exploitation of part of the resources of a lake. In Tunisia, bordigues are a state monopoly. In Madagascar, the vila are private property, sometimes of a family, sometimes of a whole village, and they can be assimilated to a traditional right. It should be noted, however, that the principal species caught, the grey mullet, are very difficult to catch with the other gears used in most artisanal fisheries.
2.2.1 An Acadja is an area with bundles of brushwood and branches planted vertically into the mud, usually at a density of about 10 branches per square metre, in a shallow lagoon (1–1.5 m depth). These tangles of small branches serve as shelter for small fishes and shrimps, and may also produce food in the form of periphyton (aufwuchs) growing on the branches. In their simplest forms, they can be quite small (5–12 m in diameter). In Ghana (my own observations) and in Madagascar (Kiener 1960), they are used solely to capture fish and they are exploited every three days. In Benin, however, such small acadjas (acadjavi) are exploited every two months (Buffe 1958), the yield from one 7 m diameter “acadjavi” being about 20 kg or an equivalent of 25 tonnes/ha/yr.
2.2.2 In Benin, many types of acadja exist (Welcomme 1971). Apart from the “acadjavi”, there are basically three types:
The “ava” which is a large acadja (mean surface: 3 628 m2 in Porto Novo Lagoon) is fished once or twice per year.
The “hanou”, where an adjacent acadja is treated as a reserve and only fished when money is urgently needed, surrounding “acadjavi” being fished frequently.
2.2.3 Welcomme (1971) has studied the variation of fish production of an acadja with age (time between fishing), and shown that the increase is logarithmic. Prior to 1959, production from acadjas in the Benin lagoons averaged 7–8 t/ha/yr. By 1969/70, this figure has dropped to 4.9 t/ha. The production could have been increased to 6.4 t/ha/ by fishing the acadjas every two months, but the labour needed to do this would have rendered the operation uneconomic. This indicates that once an ava is fully seeded, the rate of recruitment from the lagoon is greatly reduced. Production of 16 ±2t/ha are reported for ava set in lakes exploited at intervals longer than a year (Dahomey, Service des Eaux et Forêts, 1959). This is probably close to the maximum carrying capacity of an ava.
2.2.4 For harvesting, an acadja is normally surrounded with a net, usually supported above the water surface by stakes, and all the wood removed in order to catch the fish. This demands a great deal of work, particularly as the acadja has to be reconstructed after - wards. There is, therefore, a clear case for leaving an acadja undisturbed until it has reached its terminal carrying capacity (longer than one year) before harvest. With a logarithmic increase in production, a level is reached where the advantage in recruiting fish from the lake is eliminated, even with no account being taken of the work needed to harvest the fish repeatedly. It would be interesting to try harvesting an acadja with electric fishing equipment, as this would avoid the necessity to destroy and reconstruct the acadja each time.
2.2.5 Comparison of the production of a “acadjavi” (25 t/ha/yr) with that of an “ava” (8t/ha/yr) show that recruitment from the lake is not dependent on the area of the acadja. As there is no evidence to suggest that productivity could be any higher in a “acadjavi” than in an ava, the production of an acadjavi, which possibly nears maximum carrying capacity after two months (16–18 t/ha) is highly dependent on recruitment from the lake, while production from an ava is a true form of fish culture. Development for the larger types of acadja should be encouraged, therefore, while smaller ones should be studied further to ascertain whether they are not merely an efficient way of harvesting young fish of certain species from a lake.
2.2.6 The CTFT studies (1963–1965) on primary productivity in Lake Nokoué - Porto Novo, Benin, showed that planktonic productivity within acadjas was marginally lower than that outside in the same region. This may be due to reduced light penetration within the acadja, to reduced water movement, and to increased use of nutrients by macrophytic algae rather than by phytoplankton. It is likely, however, that total production of carbon is at least as high in an acadja as outside, and that this is in a form more easily used by certain fish than is phytoplankton.
2.2.7 Acadjas have been exploited on a trial basis in the Pangalanes-Est, Madagascar (Collart and Randriamanalina 1978) but with a production of only 252 kg/ha after one year. In Benin, 96% of the production of acadjas is from species Tilapia melanotheron and Chrysichthys nigrodigitatus. The relative failure of the Madagascar acadjas may stem from the fact that species adapted to this type of environment do not exist, or are present in too small a proportion of the fish present in the lagoon to seed the acadja effectively. It is also suspected that poaching took place in this acadja, which may partly explain the low yield.
2.2.8 Between 1959 and 1969, the production of acadjas in Lake Nokoué - Porto Novo lagoons dropped from 3 720 t to 1 200 t (Welcomme 1971). This may be partly due to the reduction in primary productivity of these lagoons as a consequence of the opening of the Cotonou channel, but in the same period the number of “ava” in Lake Nokoué dropped from 696 to 319. One of the main reason for this was the entry of wood borers (Teredo petiti and Bankia bagidaensis) into the lake with the higher salinities prevalent after the opening of the canal. The borers attacked the wood of acadjas greatly reducing their life. At the same time, the growth of calcareous marine organismes on the branches of the acadja substantially reduced the amount of aufwuchs available as food for the fish. Finally, the cost of brushwood had doubled within the same period and wood was no longer readily available, further increasing the cost of replacement of acadjas. Possibly, the use of materials resistant to borers, e.g. old motor tyres, could provide an equivalent substrate, at least for hanou-type acadjas, where the central “reserve” is not fished.
2.2.9 While an acadja fishery appears to increase substantially the production of a lagoon, a number of problems may be posed by such development:
Ownership: most African countries have no specific legislation to cover ownership of a given lagoon area. The exception is Madagascar, where an individual may rent a section of a lake and obtain protection of the state against poaching. In most of West Africa (e.g. Ghana and Ivory Coast) tribal rights exist in respect of portions of lagoons, and tribal chiefs are empowered to punish poachers.
The presence of an acadja fishery will displace capture fishermen from the area of the acadjas. For new developments, cooperative ownership involving artisanal fishermen of the area may solve potential conflicts.
Acadjas may be a hinderance to navigation, particularly in the case of abandoned structures which may be partly hidden under water. Allocation of areas may be made subject to the maintenance of navigation lanes, and obligation may be made as conditions for a lease to completely dismantle an acadja where continued exploitation is not contemplated.
Species composition in a lake fishery may change as a result of the proliferation of acadjas. This would only be a problem if open water species are of higher value.
2.3.1 Barachois are coastal aquaculture installations that are found only in Mauritius. The fringing coral barrier reef encloses a fairly sheltered shallow lagoon. Coastal inlets within this lagoon are cut off from the sea by dry stone walls, usually fitted with screened gates. Some barachois have fresh water entry by way of streams or natural seepage. The area of such barachois varies between 0.5 and 50 ha. Each barachois is generally stocked once a year with fingerlings of mullet (M. cephalus; M. seheli) and rabbit-fish (Siganus spp.) as well as any fingerling caught by chance while fishing for these species (Chanos chanos, Lethrinus spp. Rhabdorasgus sarda, etc.). Stocking rates are variable, but rarely exceed 1 000/ha. Harvesting is by means of drag-seines and is also usually carried out on an annual basis. Frequently, oyster farming (C. cuculata) is associated with fish farming.
2.3.2 Statistics of production exist for only one barachois but are unreliable because of poaching. Production is in the order of 100 kg/ha/yr, slightly more than twice that obtained from the open lagoon.
2.3.3 Advantages of barachois are as follows: (i) capital costs, although high initially, can be written off on a very long period, as stone walls do not deteriorate. Maintenance is low, being confined to replacement of stones knocked down by the sea, and replacement of screens and (ii) labour requirements are low, as stocking and harvesting are annual exercises.
The disadvantages are: (i) production is low, the only advantages over the lagoon being in the manipulation of the seeding and harvesting at a predetermined size. Natural seeding does occur through the screens and predators may take a heavy toll; (ii) water moves freely in and out of the enclosures through the gates and through the stone wall and, in the case of shallow barachois, 50% of the total volume may be exchanged daily despite a small tidal range. This precludes the use of fertilizers; (iii) prevention of poaching, despite the existence of laws to protect owners or leasers of barachois often costs more than the profits of the operation; and (iv) catching of seed from the lagoon may be in conflict with capture fisheries, although the small amounts involved make this unlikely.
2.3.4 Under the Mauritian constitution the creation of new barachois is very difficult, the sea being considered as public property, and alienation of any part of it whether by government or by a private individual having to be covered by separate legislation. This is a unique condition in the African countries under study. In all of them, subject to traditional rights in certain areas, government is free to dispose of any sea water area within the territorial limits.
2.3.5 Barachois are not a desirable type of extensive aquaculture development unless improved management can lead to higher production. These measures could include control of water movement in order to allow fertilization, the use of supplemental feeds, or the culture of very highly priced species (e.g. the portunid crab, Scylla serrata. oysters or shrimps).
2.4.1 As the corollary of the opening of channels into lagoons in order to facilitate seeding, the introduction of exotic species can be considered as an aquaculture activity. The circumstances in which this can be justified are when: (i) endemic species cannot fill all available niches or (ii) when an exotic species is thought to have qualities not found in local species such as higher market value, or higher production potential. In some circumstances, introduced species will not breed in their new habitat, while in others, breeding does take place. In the second case, particular care must be exercised when considering introductions, as endemic species may be displaced, and unforseen changes may occur, both to the environment, and to the behaviour of the introduced species themselves. Therezien (1976) reports that the introduction of T. rendalli into lake Kinkony (Madagascar) has resulted in the disappearance of 4 000 ha of weed beds consisting of Nymphaea, Ceratophyllum. Jussiaea, Potamogeton, Polygonum, etc. and the displacement of an abundant fish fauna consisting of Pristis, Carcharinus. Arius. Mugil (Liza), etc. T. nilotica introduced into Mauritius breeds heavily in shallow river and lake areas, but in the absence of predators to control its population, few fish have enough food to grow above a size of 15 cm.
2.4.2 The Table below (Moulherat and Vincke 1968) lists introductions into the Panagalanes (Madagascar) and the status of these introductions. In most cases, fewer than 1 500 individuals of each species were introduced and this may account for the failure of a breeding stock to be established. Most of the species are of fresh water origin, which indicates progressive freshening of the Pangalanes following the closure of the main “vinany” Only T. mossambica has become established to the point of forming a significant part of the catch.
|Sp. introduced||Origin/Year||Status in 1968|
|Osphronemus goramy||Mauritius/Indonesia||(1857)||Established but regressing|
|Cyprinus carpio||(1928)||Established in small numbers|
|Carassius auratus||(1963)||Not established|
|T. mossambica||Mozambique||(1956)||14.6% of catch|
|T. nigra||(1955)||Not established|
|Micropterus salmoides||(1955)||Not established|
2.4.3 In Lake Karoun (Egypt) a progressive increase in salinity necessitated the introduction of new fish species. From being a freshwater lake initially, the salinity of lake Karoun now ranges between 19 and 20 ‰. T. zillii was the only endemic species to survive, H. niloticus, C. anguillaris, Barbus bynni, T. nilotica disappeared, and the catch dropped from 4 000 t in 1920 to an average of 1 – 2 000 t in subsequent years (El-Zarka 1968). As early a 1938, Solea vulgaris was introduced and established successfully producing a catch of 900 – 1 000 t annually. Mugil saliens and Atherina mochon have also become established in the lake and contribute significantly to the fishery. M. capito, M. cephalus and Anguilla vulgaris failed to breed in the lake however, and fry have to be stocked every year. It is significant that these species only account for 5 % of the catch, probably because seeding is insufficient for such a large lake.
2.4.4 Concerning fish introduction and stocking in large areas, therefore, the following lessons are clear: (i) Even in a suitable environment, the introduction of insufficient numbers of individuals may limit the chances of the establishment of a breeding population, possibly due to insufficient contact between mature adults to ensure reproduction. Also, if individuals introduced are too small, survival to adult size may be insufficient to ensure establishment; and (ii) if a breeding population of a given species did not establish itself in a lake or a lagoon, further artificial stocking is unlikely to lead to a significant catch.
3.1.1 The Nile delta in Egypt is typified by a very flat topography. This has permitted the development of shallow fish ponds bounded by earth dykes, both on the strips of land between the Mediterranean sea and the coastal lakes (coastal howash), and within the lakes themselves (lake shore and lake water howash). Tang (1977) reports that coastal howash typically have a salinity between 10 and 25 ‰ and that these waters are affected by tidal action. Lake shore howash normally have a salinity of less than 5‰ and their water level is controlled by the discharge of irrigation canals or by pumping (personal observation). Lake howash have a salinity varying with location, and may have a water depth of up to 2 m. These howash are generally smaller than the others.
3.1.2 Howash management is very simple. Between May and August, when the water level of the coastal lakes is high due to increase of water discharge from the Nile irrigation system, the howash are opened. Seeding takes place naturally, with tilapia, grey mullet, catfish, perch, eel, etc. The growing period is short, as all irrigation canals are closed in January and February, and harvesting is carried out from November to January. Commonly, poultry manure is used for fertilization, resulting in average yields of 1 475 kg/ha in the Lake Manzala region (Tang 1977). Because of the short growing period, however, only 360 kg of this yield is suitable for human consumption, smaller fishes being used for animal feeds. The value of the crop is, therefore, greatly reduced. With the use of supplemental feeds, production of 3.4 t/ha are reported (personal communication, Dr. M. Ishak).
3.1.3 Some howash are located on private land, some are leased from government on short-term leases (two years generally), and some are operated by “squatters”, No precise statistics exist on the number of extent of howash farms. Dr. A.R. El Bolock (Institute of Oceanography and Fisheries) has estimated the total area of present howash farms and Tang (1977) has estimated the potential area for development on the basis of a soil survey carried out by FAO/UAR High Dam Soil Survey (Project FAO/SF:16/UAR). In order to avoid a conflict in land use, only those soils considered unsuitable for agriculture were retained for howash development, as follow :
|Type of howash||Existing howash area (ha)||Potential howash area (ha)|
|Coastal howash||4 845||4 400|
|44 000||176 000|
|48 845||180 400|
3.1.4 Although ownership of land may be in private hands, the disposal of water surfaces rests with government. Apart from improvements in management which can be effected through research and extension activities, a change of policy with respect to rental of howash areas might help to improve production. With leases as short as two years, farmers have no incentive to make any but the minimum investment needed to hold water and fish in a howash. With longer rentals, nursery areas could be built, dykes reinforced, wintering areas and techniques developed, which would eliminate the extremely wasteful practice of selling 75 percent of the crop for animal feeds.
3.1.5 The development of howash farms is justified by the relatively high production as compared to that of the lagoon. The following points should be noted:
Howash are built mainly along the shallow shore areas, which are the principal nursery grounds for the lake fishery. Reserves must, therefore, be set aside if the fishery is not to suffer.
Fishermen in the lakes believe the capture fisheries are suffering from lack of seeding due to the priority use of seed in howash. Consideration should be given to seeding howash from external sources (which might also result in more homogeneous seeding), and better use would be made of fingerlings if their use for animal feed could be prevented.
Howash are in competition with fishermen for space. Fishermen should perhaps be associated with howash development, either through cooperatives, or perhaps through the supply of seed.
3.1.6 A fish farm is now under construction at Reswa on the shores of Lake Manzala (Egypt) which will serve as prototype for future howash development, as well as being a production facility. The water supply will come from the Port Said irrigation canal to fill twelve 1-ha nursery ponds and thirty 6.5 ha production ponds. These ponds, unlike the howash which are very shallow, will be 1.75 m deep and have a 1.5 m drainage channel around the sides of the pond which will serve to capture fish and may ultimately be accepted as wintering ponds. Stocking will be with mullet and tilapia fry initially, together with some shrimp, sea bass and sea bream, and with carp later when sufficient salt will have been leached out of the soil. Fertilization will be used to increase productivity, probably mostly using phosphates which are plentiful and cheap. Pumping will be necessary both for filling and for complete drainage of these ponds. The rapid development of traditional howash farms in this area indicates a high degree of interest in fish farming, and it is to be expected that the positive features of this type of farming will be picked up readily by farmers if credit facilities and long-term leases are provided.
3.1.7 Tang (1977) in making recommendations for howash development estimated the number of mullet fry and fingerlings needed until 1982. His estimates highlight a potential major problem in Egypt. Mullet fry are at present captured routinely when they ascend the canal at El Mex to be then distributed to various aquaculture stations. This station captures 15–20 million fry annually, but survival to fingerling size is often well below 30 percent, so that the actual needs of 4.8 million fingerlings are not met. Tang estimates that 14 million fingerlings will be needed annually after 1980, which , at typical survival rates obtained elsewhere, would require 18.7 million fry. At present rates of survival, however, 64 million fry would be needed. Fry collection and acclimatisation centres are being planned near Port Said, Damietta and Alexandria. In addition, a hatchery will be constructed for induced breeding (personal communication, Mr.S. Zahlook). It is probable, however, that greater attention to the survival of wild fry would be both cheaper and more effective than to produce induced-bred mullet, a technique which is still not fully mastered elsewhere despite many years of costly experimentation.
3.2.1 Mangroves develop in intertidal zones, usually on estuarine sediments or sand flats. They are one of the zones of highest natural productivity to be found. Leith and Whittaker (1975) give comparative figures for different environments: sea and estuaries 0.7 t C/ha/yr; mean on land 3.5 t C/ha/yr; cultivated soils 3 t C/ha/yr; marshes 13 t C/ha/yr. In comparison, net primary productivity in mangrove areas in Florida is between 17.5 and 24 t C/ha/yr while total carbon fixation may reach over 50 t/ha/yr (Carter et al. 1973). The combination of such features as rock-free soils, tides for filling and draining ponds, and high productivity make ideal conditions for aquaculture pond development.
3.2.2 Estimates of mangrove areas in Madagascar amount to 330 000 ha, of which 10 000 ha are composed of small areas, mainly in river estuaries (Kiener, 1972), which are not suitable for fish pond development. Most of the mangrove areas are located on the west coast where the tidal range averages 4 m, the range of only 50 cm on the Indian Ocean side being insufficient for the formation of extensive mangrove areas, The Kenya coast also has a high tidal range (4 m) and considerable stretches of mangrove forest are to be found there, although no estimate of area could be obtained.
3.2.3 Plans are at present being finalized both in Madagascar and in Kenya for the construction of tidal fish farms in mangrove areas. In Madagascar, 200 ha will ultimately be developed principally for the culture of Chanos chanos but also shrimps (P. indicus, P. merguensis, P. monodon and M. monoceros). The culture of mullet and tilapia would also be possible (Collard and Randriamanalina 1978; Jamandre 1979). The farm planned for Malindi (Kenya), covering about 50 ha, will be used for the culture of mullet, shrimps, and possibly of tilapia and rabbitfish (Siganus spp.). Both farms will have nursery ponds and, if necessary, several stages of grow-out ponds (Sivaling am - personal communication 1979).
3.2.4 As neither of these farms is in operation, levels of production are unknown at this stage. Gatus and Martinez (1977) report that mangrove ponds in the Philippines, where conditions are similar, have an average production of 640 kg/ha/yr, mainly of milkfish, but that the best ponds produce up to 2 tons/year. In the Buguma farm (Nigeria), built in a mangrove area which cannot be completely drained because of its location in a lagoon where the tidal range is small and where seepage from rainfall is considerable, production of 2 t/ha/year of mullet, Chrysichthys and tilapia is attained with the use of supplemental feeds (M. Afinowi, personal communication 1979).
3.2.5 Gatus and Martinez (1977) list the conditions for the allocation of mangrove areas either to forestry or to aquaculture used in the Philippines. The following areas should be retained as forest lands: (a) areas needed by the local people for their domestic needs for nipa (palm leaves) and firewood, and industries dependent on firewood, charcoal and tanbark; (b) areas needed for bank and shore protection; (c) areas covered by cutting licenses and still forested; (d) swampy areas suitable for game refuge and bird sanctuaries; (e) areas needed for forest station site; (f) areas covered by existing “Other Lawful Purpose” permits except those areas covered by salt-works permits and fry grounds which should be zonified for fishpond purposes.
Alienable and disposable areas could be used for aquaculture development if the most of the following conditions are satisfied; (a) topography - swampy areas or tidal flats where there are no extensive mounds or elevations and depressions. The site should be at least at an elevation ranging from 0.3 to 1.2 m above zero datum; (b) vegetation - areas without vegetation or areas with small growth that are easy to clear instead of areas thickly wooded with big trees; (c) water supply - there should be a steady water supply throughout the year; (d) drainage - the site should preferably be capable of being drained when necessary; (e) soil - clay, clay-loam and sandy-clay; (f) flood - the site should be free from flood hazard; (g) other factors - local availability of inputs such as fish seeds, feeds and fertilizers as well as skilled manpower.
In the Philippines, 60–70 % of the mangrove areas are considered suitable for aquaculture development, but this proportion may be lower in other parts of the world.
3.2.6 In Madagascar, no forestry use is made of mangroves other than for some charcoal production and the use of stakes for fish traps. In Kenya, however, there has long been a trade in mangrove poles to Arabia as a source of bark for tannin extraction (MacNae 1974). This use has been almost discontinued as dark elements are too abundant in tannin extracts from Rhizophora and Ceriops.
3.2.7 No figures are available to establish the value of forestry products from mangrove swamps in the study area, or, for that matter, of dependent capture fisheries. However, many authors list the fish and crustacean species found in the Madagascar mangroves and insist on the importance of these areas as nursery zones for several shrimp and fish species.
3.2.8 Comparative financial returns for the use of mangroves for forestry, fisheries, nursery grounds and aquaculture are given for a swamp of 12 150 ha in Thailand by Christensen ( 1979).
|Annual gross returns|
Potential: US $ 400/ha/yr
|Nipa (palm)||230||For roof thatching|
|Shrimp culture||206||Traditional on 1 000 ha|
|Shrimp culture||2 106||Commercial scale|
|Fishery||30||Small-scale artisanal - 400 people|
|Mangrove dependent spp.||100||Fished outside mangroves|
Intensive shrimp culture gives the highest gross return from a given area, but requires the destruction of the mangroves. Under good management, if the mangroves are left untouched, the gross returns from wood, nipa and fisheries, both within the mangroves and from mangroves dependent species gives a figure of US $ 820 /ha and net returns from both uses may be comparable, as intensive shrimp culture requires a high level of investment.
3.2.9 Land use in Africa is not as intensive as in Thailand and aquaculture development need not face such competition in the use of land, but account must be taken of the need for nursery areas. It is probable, however, that only a fairly narrow strip of the mangrove along the sea front and along channels is actually used as nursery areas by shrimp and fish fry, as these can evidently not penetrate hundreds of metres into the mangrove on each tide when the area is flooded. In the Philippines, the law requires that a strip of mangroves at least 100 m wide be left as frontage to the sea, and a strip 40 m wide along each bank of rivers when fish ponds are constructed, primarily for protection of the coast from cyclone damage and from river floods. These zones, together with those which are not suitable for fishpond construction, may provide the necessary nursery areas in terms of space, but the food chain may depend on much wider areas of mangrove (Odum, 1972; Tabb et al. 1974).
3.2.10 Account should be taken of a number of factors in developing mangrove areas for fish farming, apart from the biological considerations above:
Only some mangrove soils can take heavy earthmoving equipment. This may be a drawback in some areas, but may, on the contrary, provide needed employment in others. The provision of employment may help to prevent resistance to the construction of farms from inhabitants of an area. Costs and construction time may vary considerably between manual and mechanical construction.
Access roads may be a limiting factor. Electricity requirements are low and can be provided by generators, sometimes powered by windmills.
The proximity of population centres may cause problems of pollution and theft. The potential for developing aquaculture in mangrove swamp areas in the African version is very high, however, and considerable areas may be used before the constraints mentioned above are felt.
4.1.1 At high stocking densities, the production of food in a pond at the primary, and even more so at the secondary and tertiary trophic levels, accounts for such a small proportion of the nutritional needs of the fish as to be irrelevant for all but oligo-elements. The research project being conducted at Dabou (Ivory Coast) on the culture of Chrysichthys walkerii and C. nigrodigitatus at stocking rates of 40 000/ha, can be considered to be intensive.
4.1.2 One limiting factor in high-density fish culture is the availability of oxygen if water exchange is reduced. At Dabou, a screen allows passage of water from the lagoon to the pond through a connecting channel. As the tidal range is only about 15 cm the rate of water exchange is very low. No mortalities have occurred from lack of oxygen, however, despite temperatures sometimes in excess of 30°C. The pond depth of 1,20 m may have helped in this respect, as well as the absence of fertilization. The pond can only be drained by pumping and this may lead to an accumulation of anaerobic mud on the bottom in the long run.
4.1.3 Pelleted feeds have been used, with protein content varying between 30 and 60%. The lower protein feed has given conversion rations of 3:1 when fed at the rate of 3% of the biomass. Despite the long growing period (20 months) to produce market-size Chrysichthys, the economic viability of this operation appears good, largely because of the very high market value of these species in Ivory Coast.
4.2.1 An extensive discussion of cage culture in Africa has been given by Coche (1976), but mainly for fresh waters. The development of cage culture techniques in African brackish water only started in 1976. Although some experimental cages are reported from Egypt, most of the development work in this field is at present concentrated in Ivory Coast. Several research projects are being run in various lagoons which, being fairly deep and sheltered, offer good conditions for cage culture. Work has also started on a number of commercial projects. In shallower areas, enclosures culture of fish is being developed.
4.2.2 Cage experimentation in brackish water is being carried out by the CTFT at Mopoyem, where there are facilities for fry production, and at Bingerville, where an alternative lagoon site is being evaluated (Magnet and Kouassi, 1978). Fry of Tilapia nilotica, selected for its rapid growth, and T. heudelotii, the dominant species in the lagoon of Ivory Coast, are produced in concrete breeding tanks on shore. At a size of 2 –3 cm, the fry are transferred to earthen ponds or to medium size cages (4–5 m3), where they are grown to 30 g. They are then transferred to 20 m3 cages for grow out to commercial size (180–200 g). Stocking rates for Tilapia were best when over 100/m3. Several feed formulations have been made using rice polishings, wheat, oil palm cake, cotton seed cake and fish meal. Initially, this feed was distributed in powder form through a polyethylene feeding tube, but now, sun-dried pellets are being produced using cattle blood as a binder. Protein levels average 15–16%. Growth rates are generally quite satisfactory, but unexplained mortalities of up to 67% have resulted in a very poor final food conversion (mean for 12 cages = 7.3±1.4). Fish theft was also reported to be a constant problem. From the engineering standpoint, the cages have proved to be very satisfactory. A wooden frame floated by four 200 L oil drums, supports a single net cage made of 210/48 nylon with 20 mm bar meshes; the floats have to be replaced every three years only. It appears at this stage as if depreciation on the cages could be extended to five years. Some trials have also been made with Chrysichthys nigrodigitatus from wild fry captured in the lagoon.
4.2.3 Tilapia are mostly column feeders and they adapt well to floating cages. Chrysichthys, which are essentially bottom fish do not grow so well in cages. Because of this, rearing experiments on these species conducted at Dabou by the Centre de Recherches Océanographiques have been mainly in netting enclosures (pens). Eight enclosures (25 × 25 m each) are surrounded by an outer safety net. The netting is held up by stakes, and at the bottom, it is dug into the lagoon substrate, both to prevent cultured fish from escaping and to prevent the entry of wild fish. Access to the enclosures is by a pontoon on which a house for a watchman may be built. Ideally, the area chosen should have a sandy bottom with a gradual slope and a depth of about 1 m. It should also be away from streams which might bring in chemical pollution. Fish are stocked at the rate of 80 000 per hectare, the seed being produced either in shore hatcheries/nurseries by induced breeding, or by collecting wild fingerlings trapped in bamboo sections and reared to 100 g size in ponds before stocking. In the enclosures, the fish are grown to 500 g in one year. Feeding is with pellets containing 30% protein, given at the rate of 1.2% of the biomass. Conversion ratios of 3:1 have been attained. Survival has been good, except for a mass mortality caused by oxygen depletion through eutrophication (Hem, personal communication, 1979).
4.2.4 In Ivory Coast, the above trials in cages and enclosures are being followed up by the pilot scale demonstration centres of SEPIA at Jacqueville (enclosures), which aims at producing 250 tonnes annually of Tilapia and Chrysichthys spp. and AQUICI (Aquaculture Côte d'Ivoire) at Grand Lahou, and the commercial scale production farm (cages and enclosures) of B.P. Farm Development CI. SA. near Akrou, which aims at producing 700 tons annually of these species by the fourth year (Côte d'Ivoire, MPA, 1978). It is also intended to encourage the adoption of these techniques by people living near lagoons, through extension service activities.
4.2.5 The main problems of intensive aquaculture in Africa are similar to those encountered elsewhere. In particular, they are related to:
The difficulty of obtaining sufficient seeds when they are needed. The production of seeds at the hatchery and at the nursery levels is often a major cost item, both in capital requirements and in running expenses. The fecundity of tilapias in nature is due to the large number of breeders, unlike some carps where hundred of thousands of fry can be obtained from one fish. Hatcheries therefore need many tanks and a large water flow for the production of the seeds required for a farm. Survival of Chrysichthys fry is often less than 30%.
The formulation of satisfactory feeds: the nutritional requirements of species reared in intensive conditions are not known. Complex feed formulations have been produced arbitrarily from available agricultural by-products. Artisanal fish farmers are unlikely to have access to all these ingredients, so that feeds will have to be produced commercially if intensive fish culture is to develop. More fundamental research programmes are needed if commercial producers are to provide satisfactory feeds depending on seasonal availability of ingredients.
In intensive culture, mortalities are a frequent problem. These can be either of a constant nature, fish being injured and infections or parasites spreading, or of a “catastrophic” nature due to oxygen deficiency, pollution, etc. Theft can be a serious factor perturbing cage stocking rates, the reduction in the number of fish not being immediately apparent from the presence of dead fish in the cage. Mortalities can affect the feed conversion figures substantially.
Netting enclosures are likely to suffer in the long term from degradation of bottom conditions through the accumulation of unused feeds, of fish defecations, etc. In ponds such detritus can be oxidized by drying out, or can be removed. The polyculture of detritivorous fish may help maintaining cleanliness of the bottom. Similarly, the netting cannot be removed from the water to clean off fouling organisms, as can be done with cages. However, Hem reports that T. zillii feeds on fouling organisms and could help in controlling them (personal communication, 1979).
5.1.1 Great care should be exercised in the selection of fish species for any form of aquaculture. Survival and growth of a species introduced into a new environment is of primary importance. For this, the normal and extreme tolerances to environmental changes should be known, both for the species in question and for the environment where the introduction is to take place. It should be noted that for intensive aquaculture, fish mortalities possibly account for more financial losses than do indifferent food conversion and low market value. Secondly, the reproduction of the species should be considered. In extensive aquaculture, it is generally desirable that a species should breed in an area where it is introduced. El-Zarka (1968) shows that of the six species introduced into lake Karoun (Egypt), three have established a breeding population and account for 46.7% of the total catch, while the three others which have to be regularly stocked into the lake only produce 4.9% of the catch. In more intensive forms of aquaculture, however, it is generally not desirable that a species should breed because:
energy is diverted from growth;
the stocking density may depart from optimum;
homogeneous fish sizes permit the use of optimum feeds with respect to the composition of the ingredients, the form in which it is given, and the ration. This factor may condition the type of culture installation selected to grow a given species. Tilapia, for example, may breed excessively in ponds, but will not breed successfully in cages. Finally, consumer acceptance and market value should be considered. For extensive aquaculture, to the extent that a valued endemic species is not displaced by an introduced species, this question is not of fundamental importance, as the provision of protein to poor sections of the population is usually the primary consideration. In intensive aquaculture, however, a species is often selected in preference to another due to the market value. In Ivory Coast, for example, the two species selected are tilapia (rapid growth and high production compensate for a fairly low market value) and Chrysichthys (two years to reach market size, but sold at a price 4 – 5 times higher). Depending on conditions, either species may provide the maximum economic return, but in general the first species will be chosen where production of food is the primary social consideration. The availability of export markets providing foreign currency payments may condition the choice of a high value species (e.g. Anguilla culture in Egypt).
5.1.2 The introduction of exotic species is a pratice which has come under considerable criticism. In many cases, such criticism is perfectly justified. The introduction of tilapia of various species has, in several areas, resulted in the displacement of more desirable local species. In some areas, however, local species may not fill all the available food niches, or may not be suitable for aquaculture, although this may simply be because their biology is unknown. In the former case, where the intention is to establish a breeding population, guidelines can only come from complete knowledge of the biology of the species, and from examples of its introduction elsewhere. However, an introduced species will not necessarily behave in a new environment as it will in its endemic area. In countries having water connexions with neighbouring countries, consultation should be held prior to any introduction of new species which might affect the fisheries of both countries. In the case of intensive aquaculture, experience has shown that fish escape from the best designed enclosures, and accidental introductions may occur. The same care should, therefore, be taken in evaluating the possible effect of the introduction of an exotic species. In Mauritius, a policy decision has been taken to introduce only those species which will not breed if they should escape.
5.2.1 One of the major constraints in aquaculture is the availability and cost of seeds. Where available, the capture of wild seed is always cheaper than artificial propagation as the outlay of capital is lower and the personnel employed do not need to be specialized. In some areas, behavioral aspects of the fish are used to capture their juveniles. Mullet and milkfish ascend channels leading to lagoons, power stations (Egypt) and salt pans (Madagascar) and may be captured easily there. Pools dug in mangrove swamps hold milkfish, shrimp and mullet fry (Madagascar). Oil spread on the water surface also attracts mullet fry (Nigeria) and aids in their capture. Areas with freshwater infiltrations are often particularly productive for the fry of certain species (mullet, milkfish, sparids, shrimps). Shallow weed beds are frequently productive for fry capture (siganids, cichlids). A variety of gears are used to catch fry, including fixed traps, scissor nets, seine nets and small trawls. Transport of fry from capture area to holding area may pose problems. These are solved in Nigeria by using water-filled canoes and in Mauritius by towing submerged streamlined boxes with holes to allow water exchange. Oxygen is used in some countries.
5.2.2 The capture of wild seed may cause conflicts with fishermen. In Egypt, for example, mullet fishermen believe that the 15–20 million fry captured at El Mex result in a reduced catch of adults. It is probably, in this case, that with a breeder as prolific as mullet, capture fisheries are not actually affected. This calls for the education of the fishermen and possibly for their involvement in the capture and distribution of fry. Fry used in lakeside howash farms and the reduction of nursery grounds may be harming lake capture fisheries so that conflicts of this type must not be taken lightly.
5.2.3 Artificial production of seed is, in general, only justifiable for intensive or semi-intensive aquaculture. The high level of technical skill and of capital investment needed to breed fish and to rear the young stages raised the price of fingerlings to a level where heavy mortality or escape from harvest are unacceptable. In Ivory Coast attempts have been made to breed Chrysichthys by means of hormone injections (induced breeding). This has proved successful with C. nigrodigitatus but not with C. walkeri. An “intermediate technology” solution exists for both species however, in placing sections of hollow bamboo in the lagoon. The fish lay their eggs in these bamboos which are then collected. The eggs hatch out in the hatchery where the fry are then reared. This obviates the necessity of holding adult breeding stock in sufficiently good condition to allow gonadal production, but the production of fry may be subject to fluctuation due to the availability of breeders in the fishery. This may dictate the establishment of reserve areas. Tilapia do not require hormone injection to breed, and the fry do not have to be raised in highly controlled conditions. At Mopoyen, a hatchery has been built using concrete tanks of 3.3m3, fed with a constant flow of water pumped from the lagoon. The low fecundity of T. heudelotil and T. nilotica have, however, seriously limited the output of the hatchery.
5.2.4 Hatchery production of marine species has been undertaken at Ghar El Melh (Tunisia). Sole (Solea solea) are bred within the hatchery by careful husbandry of the breeders. Gilt-head bream (Chrysophrys auratus) and sea bass (Dicentrarchus labrax) are injected with hormone HCG at a dose of 800–1 000 IU/kg. The shrimp (Penaeus kerathurus) has also bred in this hatchery, but ripe females have to be caught in the wild. In Egypt, the construction of a hatchery for the production of mullet is planned. Induced breeding of mullet has been achieved under laboratory conditions in Taiwan and in Hawaii, but is still considered to be relatively difficult. Breeders have to be captured uninjured from the wild, which is by no means easy, and the young fry stages are difficult to raise, largely because their small size makes feeding difficult. In Taiwan, where the first mullet were bred successfully, annual production is less than 25 000 fingerlings annually (Chen, 1976) - 4% of the eggs produced by one single large adult (M. cephalus).
5.3.1 The use of fertilizers is usually most profitable at intermediate stocking densities, where BOD load is not critical, and in polycultures, where maximum use can be made of the promoted growth of phytoplankton, macro-algae, zooplankton and benthic animals. In many countries, fertilizers are applied as part of pond conditioning (e.g. howash farms) but in others, associated husbandry of chickens or pigs provide a continuous organic fertilizer in the ponds (Azuretti, Ivory Coast; Côte d'Ivoire, MPA, 1978). In general, animal manures are used as fertilizers, but there is often an established use of these in crop production. In Egypt, calcium phosphate is readily available and cheap (USAID, 1978). In ponds which can be dried out, lime can be used to sterilize pond bottoms, but it is not normally otherwise necessary in brackish waters because of the pH buffer capacity of sea water.
5.3.2 Supplementary or complete feeds are used in semi-intensive and intensive aquaculture. These may be in the form of agricultural wastes used without further treatment, as in Nigeria (Buguma) where groundnut cake, rice bran and brewery wastes are fed to fish. In Tunisia, mullet fingerlings achieved good growth on broiler starter chicken feed. Maize constitutes 30% of this feed however, in a particle size which mullet cannot digest. In Israel, T. aurea which has a grinding gizzard, stocked with M. cephalus consumed the latter's droppings and could make better use of the maize.
5.3.3 In Ivory Coast, several feed formulations have been evaluated for cage and enclosure culture of Tilapia and Chrysichthys. In intensive culture, all the nutritional requirements of the fish must be met by the feed. Antibiotics are also occasionally added (Magnet and Kouassi 1978). The formulations have made use of locally available agricultural wastes (cotton seed cake, groundnut cake, oil palm cake, rice bran, wheat bran and ox blood). Competition exists for the use of many of these products, both for human consumption (groundnut cake) and for livestock production. In assessing intensive culture feed costs, therefore, it would be unrealistic to base costs on those of as yet unutilized wastes, as prices are likely to rise sharply as animal husbandry develops. Feed costs should more realistically be based on animal feed costs, as modified by particular composition (increased or decreased protein), granulation and pelleting as needed to produce water-stable feeds for bottom feeders.
5.4.1 With few exceptions, administrators in the countries visited listed as the main problem to aquaculture development the lack of sufficient personnel for the research and extension work. In several countries, this problem is high-lighted by the presence of bilateral or international experts engaged in aquaculture research. Some countries had personnel being trained abroad; in others, budgetary limitations and different priorities give little hope of an expansion of personnel. An FAO African Regional Aquaculture Centre is being established in Port Harcourt (Rivers State, Nigeria) for the training of African senior aquaculture personnel.
5.4.2 This problem points to a number of guidelines in Development Planning:
Available personnel should be concentrated on a limited number of projects. Dilution of human resources is likely to result in few projects reaching successful completion.
In the first instance, simple projects offering a good chance of success in a foreseeable future should be selected. This points to the adaptation of techniques already proved elsewhere rather than research into new techniques.
No project should be implemented which cannot find immediate application at the artisanal or at the commercial level. Artisanal projects are not likely to increase rapidly the amount of fish marketed in urban areas, as home or village consumption of the product usually takes place.
The only type of extension likely to be successful in most areas is by demonstration of the economic feasibility of a technique. Government demonstration centres are not likely to be effective in this respect, on account of the large staff normally employed, and of the fact that no person is seen to profit from the operation. Once the technical viability of a project is established, therefore, a limited number of individuals should be induced to apply it. All the necessary technical and support assistance should be provided to them, as for example in the aquisition of equipment, seeds and feeds.
Joint international ventures may be a rapid way of introducing a new technology but provision should be made for the transfer of this new technology to nationals within a limited time span. The transfer of the whole enterprise to national control should also take place timely.
5.5.1 In the countries under study, pollution has been reported to be a problem for aquaculture only in Nigeria and in Ivory Coast. In Nigeria, the pollution origin is twofold-oil pollution in the areas where tankers are loaded, and sewage pollution around densely populated Lagos. In Ivory Coast, the lagoon around Abidjan is reported to be highly polluted, although only very localized fish kills are thought to have occurred. In the lagoons further afield, pollution is reported from a banana treatment factory and from fertilizers and chemicals applied on crops and brought in by inflowing streams. The problem is serious enough to dictate the location of aquaculture facilities away from streams feeding the lagoons. Red tides have also been reported to have caused fish kills due to oxygen depletion. In most coastal lagoons (Madagascar, Ivory Coast, Benin, Nigeria) rivers and streams in floods carry considerable sediments. Although these reduce primary productivity, they are an important source of nutrients which contribute to increase lagoon productivity of the lagoons. In Madagascar, where the soil is lateritic, there might be an exception to this rule, as this type of sediment contains much less nutrients.
5.6.1 Aquaculture development is unlikely to take place if credit facilities are not available. Commercial banks consider aquaculture to be a high risk industry and are reluctant to lend money for this type of development. Most African countries have development banks established specifically to lend money for the development of agriculture, small industries, etc., usually at fairly low rates of interest. Investors in these fields, however, generally have land or equipment as security for loans, which is usually not the case in aquaculture. Governments may have, therefore, to guarantee loans to fish farmers. Concurrently, where necessary, rationalized policies on land or water tenure, on protection from theft, etc. should be formulated and enforced.
5.7.1 In all the countries reviewed, the demand for fish largely outstrips supply to the extent that fish of a very small size and often of inferior quality are easily sold. Marketing channels are frequently long, due both to the size of most of the countries involved and to difficulties of communication in many areas, both by road and by rail. Although there is generally a preference for fresh fish, most of the fish have been smoked or cooked to prevent complete spoilage of a product already undergoing bacterial decomposition.
5.7.2 Aquaculture has a major advantage over capture fisheries in that the time of harvest can be synchronized to coincide with market demand and with the means of delivering the product to market. The practice, prevalent in some South-East Asiatic countries, of marketing the product alive could probably not be justified in the African context where a substantially higher market price would not be obtained. Preservation of the fish on ice, however, should be practiced whenever feasible. Although ice melts rapidly in a hot climate, the tropical bacterial flora is not adapted to low temperatures, and even fragile freshwater species have been kept in good condition on ice for about 10 days. Practical problems are likely to arise in the implementation of such techniques of preservation. Due to the frequent practice of icing (or cooling) only fish which is in the process of spoiling, consumers tend to regard iced fish with suspicion, and this fish may be more difficult to sell than if it were not iced. Open market places would render difficult the “deception” of exposing without ice only a small part of the fish being sold. Iced fish, in those circumstances, would not fetch a higher price, and no incentive, therefore, exists for the vendor to ice his fish. Steps to be taken, therefore, include legislation; the necessary supervisory services; the provision of easily accessible ice plants, selling ice at a reasonalbe cost; liaison between producers and distributors in order that the fish should only be cropped when facilities for distribution are present; education of distributors on handling and icing the crop, and consumer education in order to remove prejudices. These questions, of course, far outstrip the context of aquaculture, but establishing the superior quality of its product may help to set the industry on a firmer footing.
Buffe, J., 1958 Les pêcheries en branchages “acadjia” des lagunes du bas-Dahomey. Bois For. Trop., 59:19–24
Carter, M.R. et al., 1973 Ecosystems analysis of the big cypress swamp and estuaries. Atlanta, Georgia, U.S. Environmental Protection Agency, region IV, SAD, EPA Report No. (904/9-74-002)
Centre Technique Forestier Tropical, 1963 Etude sur la pêche lagunaire. Nogent-sur-Marne, Centre Technique Forestier Tropical
Centre Technique Forestier Tropical, 1964 Etude sur la pêche lagunaire. Nogent-sur-Marne, Centre Technique Forestier Tropical
Centre Technique Forestier Tropical, 1965 Etude sur la pêche lagunaire. Nogent-sur-Marne, Centre Technique Forestier Tropical
Chen, T.P., 1976 Aquaculture practices in Taiwan. Farnham, Surrey, Fishing News Books Ltd., 162 p.
Christensen, B., 1979 Mangrove resources: their management and utilization for forestry, fishery and agriculture near Khlung, Chanthabrin Province, Thailand. Bangkok, Thailand, FAO Regional Office for Asia and the Far East, Draft 62 p. (mimeo)
Coche, A.G., 1979 A general review of cage culture and its applications in Africa. In Advances in aquaculture, edited by T.V.R. Pillay and W.A. Dill. Farnham, Surrey, Fishing News Books Ltd., for FAO, pp. 428–41
Collart, A. and A. Rabelahatra, 1978 Premier résultat sur les prospections et sur l'élevage de Chanos chanos à Madagascar. Antananarivo, MDRRA-PNUD-FAO, Document technique, MAG/76/002 (6):31 p.
Collart, A. and Randriamanalina, Problèmes d'aménagement écologique et piscicole en milieu lagunaire. Antananarivo, MDRRA-PNUD-FAO, Document technique, MAG/76/002 (3):18 p.
Côte-d'Ivoire, 1978 Ministère de la Production Animale, Direction des pêches et lagunaires, Rapport annuel. Abidjan, Ministère de la Production Animale, 9 p.
Crosnier, A., 1965 Les crevettes pénaeides du plateau continental malgache. Cah.ORSTOM (Océanogr.), 3(3)Suppl.:158 p.
Crosnier, A. and P. Fourmanoir, 1962 La Tsivakihiny. Nat.Malgache, 13:87–8
Dahomey, 1959 Service des Eaux, Forêts et Chasses, Conclusion d'une enquête sur la pêche dans le lac Azin Cotonou, Service des Eaux, Forêts et Chasses (mimeo)
El-Zarka, S. El-D., 1968 Rehabilitation of the fisheries of an inland saline lake in the United Arab Republic. Etud.Rev.CGPM/GFCM Stud.Rev., 35:21–42
FAO/UN, 1969 Report to the Government of Nigeria on experiments in brackish-water fish culture in the Niger Delta, Nigeria, 1965–68. Based on the work of K.K. Naw. Rep.FAO/UNDP(TA), (2759):14 p.
FAO/UN, 1969a Fisheries survey in the western and mid-western regions. Nigeria. Final report. Report prepared for the Government of Nigeria by FAO of the UN acting as executing agency for the UNDP. Rome, UNDP/FAO, FAO/SF:74/NIR 6:142 p.
FAO/UN, 1971 Rapport du Gouvernement du Dahomey sur l'évolution de la pêche intérieure, son état actuel et ses possibilités. Basé sur le travail de R.L. Welcomme. Rapp.FAO/PNUD(AT), (2938):97 p.
Fourmanoir, p., 1953 Notes sur la faune de la mangrove dans la région de Majunga: crabes, crevettes, poissons. Nat.Malgache, 5:87–92
Fourmanoir, p., 1957 Poissons téléosteens des eaux malgaches du canal de Mozambique. Mem.Inst. Sci.Madagascar(Sér. F), (1):317 p.
Gatus, A.R. and E.S. Martínez, 1978 Engineering considerations in the release of mangrove swamps for development into fishponds. Manila, South China Sea Fisheries Development and Coordinating Programme, SCS/GEN/77/15:85–95
Jamandre, T.J., Jr., 1979 Technical assistance to the proposed brackishwater aquaculture centre for Madagascar. A report to the Government of the Malagasy Democratic Republic. Antananarivo, Madagascar, FAO/UNDP, MAG/76/002:51 p.
Kiener, A., 1959 La pêche au Zompona. Rev.Madagascar, 7:47–54
Kiener, A., 1960 La pêche au piège ou “vovomora” dans les Pangalanes-Est. Bull.Madagascar, 167:309–14
Kiener, A., 1965 Contributions à l'étude écologique et biologique des eaux saumâtres malgaches. Les poissons euryhalins et leur rôle dans le développement des pêches. Vie Milieu(C Biol.Terre), 16(2):1013–149
Kiener, A., 1972 Ecologie, biologie et possibilités de mise en valeur des mangroves malgaches. Bull.Madagascar, 308:50–80
MacNae, W., 1974 Mangrove forests and fisheries. Indian Ocean Fishery Commission. Rome, FAO, IOFC/DEV/74/34:35 p.
Magnet, C. and S. Kouassi Yao, 1978 Essai d'élevage de poissons en cages flottantes dans les lagunes Ebrié et Aghien. Nogent-sur-Marne, Centre Technique Forestier Tropical, 49 p.
Martosubroto, P. and N. Naamine, 1977 Correlation between tidal forests (mangroves) and commercial shrimp production in Indonesia. Mar.Res.Indonesia, 18:81–6
Moulherat, J.L. and M. Vincke, 1968 Etude en vue du développement de la pêche aux Pangalanes-Est. Rapport au Gouvernement de la République Malgache. Tananarive, Centre Technique Forestier Tropical, 195 p.
Odum, W.E., 1972 Pathways of energy flow in a South Florida estuary. Univ.Miami Sea Grant Tech.Bull., (7)
Ravagnan, G., 1978 Coastal aquaculture systems for fish and crustacea in the Mediterranean. Paper presented at the Expert Consultation on aquaculture development in the Mediterranean region, convened by the Government of Greece in cooperation with FAO (GFCM) and UNEP. Athens, 14–18 March 1978, UNDP/WG-15/4:46 p. (Restricted)
Rhouma, A. and A. El Ouaer, 1978 L'aquaculture en Tunisie: potentialités et techniques d'élevage. Rapp.Doc.Inst.Natl.Sci.Tech.Océanogr.Pêche, Tunisie, (4/78):3–46
Tabb, D.C., B. Drummond and K. Kenny, 1974 Coastal marshes of Southern Florida as habitat for fishes and effects of changes in water supply on these habitats. Coral Gables, University of Miami, Final Report to U.S. Department of the Interior, B.S.F.W. Branch of River Basins. Contract No. 14-16-0004-56
Tang, Y.A., 1977 Report of the Aquaculture Mission in Egypt, 20 October – 28 November 1976. Rome, FAO, 48 p. (mimeo)
Therezien, U., 1976 Données sur Chanos chanos Forskãl 1775 à Madagascar. Bull.Cent.Etud.Rech.Sci., Biarritz, 2(1):35–52
Turner, R.E., 1977 Intertidal vegetation and commercial yields of penaeid shrimp. Trans.Am. Fish.Soc., 106(5):411–6
UNDP/ADCP, 1979 Development of coastal aquaculture in the Mediterranean region. Report of a mission to formulate a cooperative programme of activities. October 1978 – February 1979. Rome, UNDP/FAO, ADCP/MR/79/5:155 p.
USAID, 1978 Report of USAID Aquaculture Mission to Egypt. Cairo, USAID, 78 p.
Verdeaux, F., 1979 La pêche lagunaire en Côte-d'Ivoire. Contexte sociologique et formes d'exploitation du milieu naturel. Communication au Séminaire Unesco sur les Ecosystèmes côtiers, Dakar, juin 1979
Vincke, M., 1977 Situation des pêches continentales en République de Côte-d'Ivoire. Rapport de Mission. Rome, FAO, 27 p.
|Species Cultured||Côte d'Ivoire||Benin||Egypt||Ghana||Kenya||Madagascar||Mauritius||Nigeria||Tunisie|
|Scylla serrata (crab)||X||X||X|