Professor of Zoology
Department of Zoology
University of Nigeria
The paper draws attention to current efforts being made to maximize fisheries production from the extensive floodplains (fadamas) of the Niger-Benue drainage system through development-oriented studies on fish culture in seasonal and perennial natural lentic waters. It is suggested that maximal production from floodplains can best be achieved through integrated development planning by all interested agencies.
Le document attire l'attention sur les efforts entrepris pour accroître la production de poisson des plaines inondables (fadamas) du système de drainage du Niger-Benue au moyen d'études orientées sur le développement de la pisciculture dans les eaux lentiques naturelles, saisonnières et intarissables. Il en ressort que l'on peut obtenir une production maximale des plaines d'inondation au moyen d'une programmation de développement intégré par tous les organes intéressés.
The economy of riverside peoples in Nigeria is based not only on activities in the main river channels but also, and perhaps more importantly, on the associated rich alluvial plains or adjacent lands which are flooded regularly, and usually annually, by the river. These annually silted floodplains are locally called the “fadama”.
The contributions of the floodplains of the Niger-Benue river complex in crop, livestock and fish production came into sharp focus with the recent construction of a number of multipurpose dams in Nigeria. Because of its location and size, the Kainji dam on the upper Niger produced the widest and most dramatically noticeable effects on agricultural and fisheries production of downstream areas from New Bussa to the upper reaches of the Niger delta. As might be expected, because of the contribution of local rainfall to the annual flood, this effect of the dam is inversely proportional to the distance downstream of the dam site. It is perhaps largely correct to indicate that the aftermath of Kainji did more than anything else to direct the attention of Nigerian biologists and agriculturists to the need for studies aimed at developing management and conservation procedures for protecting and maximizing the utilization of major floodplains in the country.
This paper draws attention to current efforts being made to maximize fisheries production on the great and extensive fadamas on the Niger-Benue drainage system by development-oriented studies on fish culture in seasonal as well as perennial natural lentic waters.
2.1 Reasons for Fish Culture in Natural Waters
It is perhaps important to underline the fact that so far most fisheries biologists, both Nigerian and foreign, have tended to hold the view that fish culture in general is not recommended or feasible for most areas in the Nigerian Niger-Benue floodplain. Reasons advanced to support the above viewpoint include the high evapotranspiration rate in the middle Niger and Nigerian Benue which raises doubts about the life span and thus availability of excavated pond water for continuous culture. It is also held that under the present conditions, fish culture is unlikely to be profitable and what is more, does not offer scope for significant increase in fisheries production in the area (Mutter, 1972b). Even the tainting of flavour of cultured fish is advanced as an economic consideration against culture (Mutter, 1972a). The fact that cheaper capture fisheries have not been fully exploited is also held against fish farm development.
While it is accepted that some of the factors such as the availability of water for long periods and the high inputs for artificial farm pond development are important and valid considerations, the present low level of national protein intake, the fish supply and demand situation as well as fish consumption preferences of the people of Nigeria inter alia, should receive due consideration, if not over-riding weighing, in decisions regarding the development of fish culture.
2.1.2 Supply demand situation
The current demand for fish is about twice the level of local production from all sources. In many parts of the country especially the southern areas, fish may constitute over 40 percent of human protein intake. Indeed, fish forms the dominant source of available animal protein in riverine areas and most parts of the hinterland of the lower half of Nigeria. In the latter area also, the demand for freshwater fish is very high and people are prepared to pay more for this commodity (which also serves for seasoning foods) in preference to cheaper saltwater fish. From longstanding orders for cultured carp and tilapias at Government fish culture demonstration farms in both Western and East Central States, there is no doubt that the flavour factor is unlikely to be a practical consideration in the country for a long time to come.
Informed projections on fish production and demand made at the National Agricultural Development Seminar in 1971 emphasized this shortfall between supply and demand. Thus while the estimated maximum sustainable yield from all sources was 484 000 metric tons, the demand for human consumption alone for the target years 1975, 1980 and 1985 were 574 000, 830 000 and 1 229 000 metric tons respectively. Fish demand for the preparation of animal feeds was not given.
The indicated wide deficits in fish supply and the persistence of protein deficiency diseases in the country call for immediate mobilisation of all available inland waters for maximal production. It seems obvious that one of the readily available paths through which the projected maximum sustainable yield can be further increased is by fish culture. While the coordination and other problems of artificial fish farming, as suggested by FAO (1966), are being sorted out by the Federal Department of Fisheries, the cheap facilities for culturing fish offered by the extensive natural residual lagoons, lakes, ponds and pools of the Niger-Benue fadamas should be put to immediate use to increase fish production by culture. It is pertinent to note that this line of action is already being pursued in a few of the adjacent river systems in the country. For instance, even in the drier and hotter far northern areas, culture trials in fadama lakes is a component of the integrated development of river floodplains as in the Hadejia River Project in Kano State.
2.2 Relevant Physiographical and Climatic Features
Considerable data on the present features of physiography and climate of the Niger-Benue floodplains are given by Mutter (1972a and b; 1973). Since the culture media under consideration are natural lentic bodies of water which are already in existence, details of such pondfarm limiting factors as soils, topography, water supply etc.. do not require extensive discussion here. Therefore, only the salient features to show the extent and quality of the resource are briefly outlined below.
2.2.1 Niger floodplain
The lower Niger floodplain stretches from the extensive coastal brackishwater areas to the confluence of the Niger with the Benue at Lokoja (Fig. 1). South of Onitsha, the fadama, 30–40 km wide, is intersected by many channels with numerous perennial and seasonal ponds (Fig. 2). From Onitsha to Ida (Fig. 3) the floodplain gradually widens to about 40 km, almost all of this lying between the Niger and the Anambra River to the East. The last stretch of the floodplain from Ida to Lokoja is narrow with very few perennial ponds (Fig. 4). At flow peak, the freshwater sector from the apex of the delta to Lokoja has an area of about 6 350 km2 (Mutter, 1973).
Fluvisols are dominant in the floodplain of the Niger and its tributaries but its complex pattern in the alluvial areas where heavy texture with poor drainage is interspersed with more sandy and well drained patches is very important in considering schemes for increasing the size of natural fadama ponds (see below).
Characteristic climatic features include high humidity (60–80 percent) with mean annual temperature ranging from 26–28°C. The rainy season lasts from April to September and causes the heavily silted single annual flood, the “white flood”, experienced in the are. Annual average rainfall varies from 2 500 mm at the apex of the delta to 1 200 at Lokoja (Mutter, 1973).
Vegetation cover commences with mangrove swamps of the coastal and deltaic brackish waters, through freshwater swamp forests, to riparian forest and savanna mosaic at the northern limit.
The fadama area of the remaining upper portion of the Niger is generally narrow with fewer perennial lakes and ponds compared to the lower Niger (Fig. 4). Its is estimated that up to 5 percent of the floodplain may be covered by seasonal and perennial lentic waters. Because of the Kainji dam, the future of these lakes and ponds is uncertain.
The area is drier and hotter with average annual rainfall of 1 125 mm and annual temperature range of 21–38°C.. The rainy season is from April to October and results, as in the Lower Niger, in a single “white flood” which peaks usually about September/October. The pre-Kainji siltless “black flood” which used to peak about January/February in this area and derived from a prior six months monsoon rains outside Nigeria, has been obliterated by the Kainji dam.
Guinea savanna dotted with trees and shrubs forms the dominant vegetation over the entire area and therefore provides little cover for natural lakes and pools. These consequently lose more water by eveporation during the dry season than their counterparts in the lower Niger floodplain.
2.2.2 Benue floodplain
With the exception of the sector at the Cameroon border, the floodplain of the Nigerian Benue with an area of about 2 415 km2 and stretching for about 905 km from the frontier to Lokoja, is generally narrow and has fewer perennial lakes and ponds than the Niger system (Fig. 1 and 5).
Heavy clay soils with occasional vertisols in the backswamps predominate. These are seasonally inundated with floods of up to 6 m from July to December.
Vegetation and climatic features closely approximate those of the middle Niger. The climate is warm and humid with mean monthly temperature and average rainfall of 25–30°C and 1 125 mm respectively. The rainy season lasts from March to November with most of the rain falling from June to October. Scant vegetation cover is provided by savanna woodland.
2.3 Water Quality
Very little published information is available on the physical and chemical characteristics of the Niger-Benue floodplain lentic waters and associated main river channels. From Welcomme's (1974) review of what is known of these factors in other African systems, it seems likely that these parameters for the Niger-Benue system would approximate the more general African conditions.
Such important factors as pH, dissolved oxygen, conductivity and current characteristics of the floodplains are known to be closely related to the flood cycle. Dissolved oxygen is generally higher in both the floodplain lentic waters and river channels during the floods. Conductivity, usually an index of total ionic concentration, on the other hand, tends to be higher in the dry season than in the wet. Holden and Green (1960) are of the view that the total salt concentration remains the same but that the lower figures during the flood may be due to dilution.
The most variable factor between different African systems is pH. This variability is thought to be related to soil factors. However, Holden and Green (1960) observed that in the lagoons of Sokoto River, a tributary of the Upper Niger, pH tended to alkalinity due to the concentration of calcium by evaporation.
The existence of water currents on the floodplain, except perhaps during late dry season when the fadama lakes and pools are completely isolated, is a feature which no doubt contributes immensely to the maintenance of the physico-chemical qualities of fadama lentic waters and consequently, their capacity to support the characteristic fish fauna/fisheries of the area.
3.1 Levels of Cultural Practices
3.1.1 General situation
In the traditional riverine fishing community in Nigeria, the development of culture fisheries has lagged behind capture fisheries. However, fulltime fishermen in practically all sectors of the Niger-Benue floodplain have for long realized that the seasonal as well as perennial pools, swamps, lakes and lagoons of the fadama form a rich and surer source of fish than river fisheries during the dry season. This had led over the years to local and uncoordinated attempts to convert some of these floodplain ponds and swamps into what can be rightly described as extensively managed and largely unfed “culture ponds”. The level of management depends on whether such ponds are communally or privately owned also their distance from settlements or villages.
Privately owned ponds near villages or temporary ferm settlements are usually partially fed and fertilized with agricultural wastes and household sweepings. On the other hand, communal lakes and ponds, whether seasonal or perennial, are unfed.
3.1.2 Niger floodplain
The lower Niger has the best known cases of partially managed and fed natural fish ponds. The rich triangular floodplain between the Niger and Anambra rivers has over 52 large perennial lakes and ponds, largely under private ownership with a total dry season surface area of about 1 650 hectares (Awachie, 1973). The practice of dumping rice husk and maize wastes from local mills on the edges of perennial lakes and ponds and even the river channels is widespread here. Local farmers, who are also part-time fishermen, are aware that this practice helps to fertilize the ponds as well as provide fodder for herbivorous fish such as the “river cow” Distichodus spp. and some omnivorous. It is noteworthy that about 70 percent of the fish sold at Otuocha, Onitsha, and Ogrugu during the dry season consist of Clarias, Heterobranchus, Gymnarchus, Distichodus, Ophiocephalus and Citharinus species “cultured” in these semi-fed and unfed ponds.
At Atani and Odekpe, south east of Onitsha, supplementary feeds are provided, as indicated above, by household wastes such as dry cassava peels which find their way into smaller and continuously cropped family ponds. Here also the construction of temporary dwarf earth dams across outlet channels, not so much to retain water as to prevent fish from migrating back into the main river channel with receding floodwater, is common.
Similar semi-culture but more rudimentary practices exist all over the Niger delta including brackishwater areas. Unlike in the upstream freshwater areas, the saltwater zone has mainly perennial lakes and ponds which are replenished daily by tidal flow. To retain fish, therefore, various combinations of barriers involving sticks of mangrove and raffia palm as well as wire mesh are built round the ponds/pools as necessary. The arrangement ensures free flow of water with minimal loss of fish.
3.1.3 Benue floodplain
Most of the perennial fadama lakes and lagoons are communally owned and unfed. Indeed, it is perhaps correct to indicate that, traditionally, very little if any attempts are made to manage these bodies of water to improve their productivity.
3.2 Specific Composition of Managed Natural Stock
Field interviews with fishermen do not seem to indicate that stocking of fadama lakes and ponds is a long standing practice. The stocking of backyard natural ponds with fingerlings of various fish, especially clariid species, taken along temporary barriers across receding flood waters and observed during 1965–1974 in the Atani/Odekpe and Oguta areas of the lower Niger, would appear to be a relatively recent development dating back to about only six to seven generations.
The species managed and/or semi-cultured are, from the above indications, those which (as traditional fishermen are fully aware) are hardy to handle and are naturally adapted to surviving in such bodies of water. These species include those which seasonally undertake lateral migrations to the inundated fadama pools and swamps which serve as breeding and nursery grounds. The dominant elements are catfishes such as Heterobranchus, Clarias, Synodontis, Chrysichthys, Malapterurus, as well as others such as Polypterus, Protopterus, Gymnarchus, Heterotis, Xenomystus etc. which are known to possess suitable adaptive features for living under low oxygen conditions of floodplain lentic waters during the hot dry season. Common but minor elements in such ponds include some cichlids especially Sarotherodon (=Tilapia) and Hemichromis, citharinids, cyprinids, mormyrids and characids.
3.3 Cropping Procedures and Productivity
Large lakes and ponds whether private or communal, are harvested annually, usually at the of the dry season when catches from the main river channel are very poor. It is often the practice of migrant fishermen to purchase fishing rights of privately owned ponds and then crop them under agreed terms. Dry season communal fisheries activities in both unfed and semi-fed fadama lakes and pools have led to the development of annual “fishing festivals” which are fast becoming a tourist attraction. Indeed, the Argungu fishing festival on the floodplain of Sokoto River is today an event of some international significance.
Smaller semi-fed family ponds are subjected to continuous cropping to meet household requirements. The mode of cropping is related to the topography, as well as the nature, size and depth of the “pond” and shows local variations.
In the few completely harvested ponds, which are usually purchased ponds, water is either evacuated by means of hired pumps or by cutting shallow canals as is more normally done in the lower Niger. In swamps and pools, the canals are usually very long and often blind. Stranded fish as well as those that move into the canals are easily picked up. Welcomme (1971) has described a very similar procedure for the Oeine River floodplain in Dahomey.
Larger fadama lakes and lagoons are cropped with all available gear ranging from local traps, weirs and scooping gear to gill and castnets as well as longlines. As might be expected, these larger perennial bodies of water are never completely fished out.
From the foregoing, it can be readily appreciated that although these natural ponds are rich, their mode of exploitation has made any reliable assessment of their yield almost impossible. It is hoped that data from experimental natural lakes and ponds in the Atani/Odekpe area and Do-Anambra floodplain will provide some useful indication of their productivity.
4.1 Available Media for Culture
As can be readily surmised from the foregoing, the main bodies of water to be involved are suitable floodplain lagoons, lakes, ponds and pools already existing in natural depressions as well as swamps fringing the main river channels. To be included also are swamprice fields with a suitable level of water for a desired period. The above will provide the mainstay of fish culture in natural waters.
As an important supplement to the above, natural as well as artificial human water supply reservoirs and even the flood control reservoirs projected for the Niger-Benue system, will be harnessed for fish culture in the present context.
Depending on their life span and the length of time they are available for fish culture during the flood cycle, the above media may be utilized as seasonal or perennial farms.
4.2 Species for Culture
Both local and acclimatized exotic species which have proved successful so far in the country will be utilized. Under this class are the mainstay of tropical fish culture, viz.: tilapia and carp. Their fry and fingerling supply problems are well known and a number of farms now produce their fry for sale.
Particular effort will be made to use those local species which naturally inhabit the media to be employed for culture and which were listed above. It is also noteworthy that a number of these species are currently being developed for culture. Those which have shown great promise and may be described as even popular in freshwater ponds include Clarias spp., Heterobranchus spp., Heterotis niloticus, Chrysichthys nigrodigitatus, Lates niloticus, Gymnarchus, and to a lesser extent Citharinus spp.
The culture drawbacks of tilapias viz liability to precocious breeding and consequent runting can be turned into a cultural advantage by cropping tilapia farms continuously as is the practice in intensively managed farms in Western Nigeria. Also, fast breeding tilapias can be reared as trash fish either in mixed or polyspecific culture with highly-priced carnivorous fish such as Lates niloticus or Gymnarchus niloticus; alternatively, they can be reared in monospecific culture and then used to feed the latter species.
In the brackishwater areas of the Niger delta, readily available euryhaline species, apart from tilapias, are C. nigrodigitatus and the mullets especially Mugil falcipinnis.
At the moment the fry/fingerlings of these species are collected from natural sources - the fadama and brackish waters.
4.3 Available Preliminary Data
4.3.1 The Atani experiment
Field trials at Atani on the lower Niger floodplain during 1968–70, when other fish culture farms in the former Eastern Nigeria were unavailable because of the civil disturbances showed that by skilful management of the fadam floodwater it is possible to culture fry/fingerlings to the harvest stage under almost purely natural conditions (Awachie, 1968, 1969, 1973). Fry and fingerlings collected with the aid of a task force of experienced local fishermen from receding floodwater were used in stocking the main types of natural waters chosen for the trials viz.: floodplain ponds at Atani, a cut-out lake in the hinterland, and kraals or fish-pens at the periphery of Oguta lake, Njaba and Idamili Rivers.
To collect sufficient fry/fingerlings quickly and safely, earth-backed palm frond barriers were erected across minor receding channels and along the edge of shallow flooded pools or selected areas of the floodplain. Fingerlings and fry were then readily scooped into all available containers. Large calabashes and open tins were most commonly used in delivering fish to desired locations. About 50 percent of cultured specimens came from traditional “fry fisheries” which involve large locally made lift devices as well as lift nets installed at the river-sides as floods recede, and used to lever out large numbers of mixed fry/fingerlings from grassy river or pool edges. The main source of fingerlings after flood recession were the smaller floodplain pools which were surrounded with small earthwork during late flood phase.
Two ponds, 0.6 and 1.5 ha respectively, conveniently located near the task force fishermen's homes and almost encircled by dwarf earthwork as the flood receded, were left unfed for five months and then harvested. The average yield was 250 kg/ha with clarids, mochocids and gymnarchids being the dominant fish. On stocking the same ponds, each with 1 000 Clarias fingerlings and 1 000 cichlid fry and fingerlings from nearby ponds, the yield after six months with very little feeding was 657 kg/ha. The harvest included Synodontis spp., Hydrocyon spp. and notopterid species.
Because of extensive poaching activities caused by wartime conditions, it was not possible to quantify with reasonable accuracy the yields from the partially-fed hinterland lake and two kraals stocked with Clarias spp. and Tilapia spp; tilapia and carp; and Parophiocephalus spp. respectively. However, the estimated yield from the lake varied from 900 to 2 060 kg/ha/yr. It may also be pointed out that because of widespread acute shortage of protein during the period, the then Head of the Fisheries Operations (the present author) was inevitably more interested in getting the harvests out to the people than in the accuracy of production records.
Reed (FAO, 1969) described a similar experiment on the Niger floodplains near Lokoja. By constructing earth weirs across exit streams from a swamp/lagoon system to increase the volume of water, he recorded a harvest of 188 kg/ha from unfed ponds. This figure was estimated to be double the normal yield in previous years.
4.4 Proposals for Natural Pond Culture
From the above review of available information on the practice and prospects of floodplain pisciculture on the Niger-Benue system, it should be clear that both seasonal and perennial culture practices can be undertaken. Despite the fact that ponds are readily available and water delivered naturally, there are attendant constraints in their utilization. It is not possible to exercise effective control over the fish species which will pass into the culture media during the flood. Even with pre-culture cropping involving local pool-fishery methods which spare neither adult nor fry, undesirable species especially ubiquitous tilapias and Hepsetus odoe, cannot be eliminated as experience in artificial pond farms have shown.
Other constraints such as ownership/tenement problems as well as institutional and allocative conflicts in the use of the fadama lakes may be easier to contain by not only demonstrating the profitability of the proposals but also getting the local floodplain farmers and fishermen involved.
Because of the water supply characteristics, perennial culture can only be meaningfully undertaken in lakes, lagoons etc. Which meet most of the following requirements:
Location on the outer limit of the floodplain
Maintenance of a desired minimal water level all the year round
In the drier areas, a considerable proportion of the water supply (ca. 50 percent) should be derived from the catchment area (as distinct from the river channel) in order to ensure the maintenance of reasonably good water level through most of the year
Channels connecting them to the main river should be narrwo and reasonably shallow. Those which become functional only at the flood peaks because of higher location of the ponds are the best since they can easily be cut off with earth dams.
Similarly, swamps in shallow depressions with minimally suitable level at the of the dry season can be put under semi-culture to increase their yield. As for lakes and ponds, the volume of water in them could be increased as desired by constructing earth dams across connecting channels. This procedure will no doubt improve the value of traditional swamp fisheries on the floodplains. The salient features of the above proposals are summarized in Table I.
To minimize the problem of eutrophication in adjacent fadama ponds found unsuitable for culture, fertilization of culture ponds should be carefully controlled.
4.5 Conversion Procedures
The limitations imposed by the flood regime make it almost impossible for the seasonal as well as most perennial bodies of water to be put cheaply under culture for more than eight months without constructing expensive barriers to control water supply. To achieve maximal utilisation, and bearing in mind the various types of fish culture activities to be undertaken, the following procedures are suggested for converting floodplain lagoons, lakes, ponds, and swamps into culture media.
Proposed schedule for fish culture in fadama lentic water
|Type of media||Minimum effective life span||Culture indicated||Indicated pre-culture activity||Fish/culture indicated|
|Deep lagoons||Perennial||Largely unfed||Early pool fishery||Fast growers, mono or polyculture|
(ca. 6 months)
|Intensive||Early pool fishery||Fast growers, monoculture|
|Lakes||Perennial||Unfed or intensive||Early pool fishery||Commercial species, mono or polyculture|
|Large ponds||Perennial||Intensive||Early pool fishery||Commercial species, mono or polyculture|
(ca. 6 months)
|Intensive||Early pool fishery||Fast growers, monoculture|
|Intensive||Early pool fishery or NIL||Fast growers, nursery ponds|
|Large swamps||Perennial||Unfed or partially fed||NIL||Siluroids, polyculture|
(ca. 6 months)
|Unfed, fertilized||NIL||Nursery for natural stock, polyculture.|
|Swamp rice fields||Seasonal |
(ca. 6 months)
|Fertilized, unfed||NIL||Hatchery/nursery for tilapia etc.|
(a) Seasonal nursery farms (natural stock)
To achieve an extension of the natural nursery role of the fadama, the following sequential activities may be undertaken:
(b) Seasonal hatchery nursery (chosen species)
(c) Rearing ponds (natural stock)
(d) Rearing ponds (chosen species)
Perennial Culture Activities
(e) Hatchery/nursery (chosen species)
Year 2 etc.
(f) Rearing farms (chosen species)
Year 2 etc.
The above mentioned conversion schemes are to serve as guidelines and may be modified according to the requirements of limiting local cultural parameters.
5.1 Existing Schemes
5.1.1 Buguma scheme
Consequent on the investigations of Pillay (1962, 1968), a pilot project was established at Buguma to determine the potential of brackish water fish culture in the Niger delta area. Activities which were suspended during the civil disturbances in the country, are now being gradually resumed. Recent reports indicate that the monitoring of physical and chemical parameters of the media for culture has been recommenced. Also preliminary production trials in reactivated ponds under different water supply regimes, using grey mullets supplied by local contractors and fisheries staff, are already under way.
Other pilot trails in the same ecological zone but not on the Niger-Benue system may be briefly indicated because of their relevance to the subject.
5.1.2 Opobo scheme
This is currently being undertaken by the South Eastern State Fisheries Division of the Ministry of Agriculture and Natural Resources. Investigations here concentrate on concurrent production trials using three euryhaline species, Tilapia, Mugil and Cyprinus, which are reared in adjacent freshwater and brackishwater ponds. The freshwater ponds are filled with water from the catchment area while brackish water ponds are supplied by tidal flow. Both mono- and poly-culture are involved. Results from these trials are not yet available for publication (Essien, personal communication).
5.1.3 Lagos trials
These are based in brackishwater ponds associated with the extensive Lagos lagoon and were commenced during the civil disturbances when Buguma facilities became unavailable. Minimal earth movement to deepen the pools was involved and the experiments concentrate on the use of the euryhaline and readily available species of Tilapia and the catfish Chrysichthys nigrodigitatus.
Production estimates based on yields from polyculture ponds, fed with a mash comprising groundnut cake, maize, beans, garri and palm oil was 2 412 kg/ha. C. nigrodigitatus contributed 38 percent and Tilapia 58 percent of the above yield (Sivalingam, 1972).
In unfed and unfertilized ponds, natural entry of mullet fry with tide was found to result in production of up to 239 kg/ha/yr (Sivalingam, 1973). Mullet fry are available throughout the year in coastal brackish water areas of Nigeria, with greater numbers occurring during March-July. It is also estimated that enough mullet fry to stock 10 000 ha can be collected from these coastal areas (Sivalingam, op.cit.).
Developmental studies by Ezenwa (1973) have established some of the parameters for acclimatizing grey mullets in freshwater ponds. The size of fry, pH and salinity were found to be limiting. Thus mullet fry, 2.00–3.00 cm in length, collected from brackishwater (salinity 22.5 percent) can be successfully cultured in freshwater (salinity zero percent) at pH 7.0–7.5 with little or no mortality.
5.2 Proposed Schemes
It is planned to establish pilot production trials in floodplain pools, lakes, lagoons and swamp rice fields in conjunction with and/or without field crops production in the following areas:
Preliminary feasibility studies within the framework of regional development plans are being undertaken to determine the number and hectarage of the most suitable bodies of water to be involved as well as the best organizational set-up to undertake these pilot trials.
Apart from its traditional role in field crop production, livestock grazing, intensive dry season pool fishery and extensive flood phase fisheries (Welcomme, 1974), there are plans to develop the following on the floodplains of the Benue and its major tributary, the Gongola River:
Similar agro-industrial developments exist or are planned for the Niger system, e.g. Nigerian Sugar Company Bacita, South-east of Jebba, as well as the Tiga and Bagauda complexes near Kano. The present and projected new uses of the Niger-Benue floodplain would have considerable bearing on the above proposals for fish culture in fadama lakes and ponds, and vice versa. These are briefly reviewed below.
6.1 Effects of other Developments on Fish Culture
As might be expected from the foregoing these developments will have positive and/or negative components on schemes for fish farming. The major considerations are briefly dealt with as follows.
As was experienced with Kainji, dams will reduce the number, size and life span of pools, swamps, lakes and lagoons available for fish culture especially in downstream areas. The present situation with natural lentic waters in the Ndakalowu, Tada and Sunti areas, south-east of Jebba is a case in point (Fig.8 and 9).
Fry/fingerlings supply from natural sources on which the present proposals will rely heavily, particularly at the initial phase, will be adversely affected. In upstreams stretches, this often results from the barrier to spawning migration imposed by the dam while downstream, the reduction in flood level produces a similar effect (Welcomme, 1974). It is, however, noteworthy as the latter author reports, that in adjacent downstream areas where topographical considerations permit, water from the reservoir could be canalized into the affected natural lakes and ponds to minimize this effect. The recent experience with the Strijdom dam on the Pongola River is relevant here.
6.1.2 Livestock grazing
Most parts of the Savanna zone of the Niger-Benue floodplain are used intensively for livestock production during the dry season. Pools and lakes are used for watering cattle and in the drier northern areas this practice contributes to the shortening of the life span of seasonal pools. Indeed, cheap earth-dams are often built across small seasonal and perennial rivers to provide longer lasting watering points (tapki) at the peak of the dry season. Large tapkis with long life span could be put under fish culture to maximize their use. Stauch (personal communication) has admonished the exercise of caution in the adoption of tapkis for culture purposes since they are liable to gross pollution as discussed below.
On the positive side, the droppings of livestock will help to fertilize culture ponds during both dry and wet seasons.
6.1.3 Field crops
The major beneficial influence of field crop activities on floodplain fish farms is that vegetable remains and damaged seeds, e.g. maize, groundnuts etc., provide cheap sources of fodder and feed, while coarse crop remnants are used to increase their fertility.
Field crop procedures may however impair the maximal use of floodplain pond water by increasing water loss to irrigation and by reducing the water income from the catchment area as a result of ridging operations. An allied unsalutary effect of ridging and tilling is that they accelerate the filling of culture ponds as a result of erosion.
Agricultural procedures in large-scale farm units located on or near the floodplain usually involve the use of chemical fertilizers and insecticides to increase yield. Pollution from these sources and the consequent problem of eutrophication from polyphosphates etc. will become an increasingly important consideration in the planned utilisation of natural lakes and ponds for fish culture.
As elsewhere, current trends in development planning of agricultural production aim at the establishment of complexes including agro-based industries. On the floodplain, industrial water supply requirements and pollution resulting from the discharge of effluents from industrial plants will impair their use and may minimize the effectiveness of natural pond water for culture.
On the other hand, the presence of these industries will reduce the cost of intensive fish culture by providing cheap wastes which can be used as feeds and fertilizers. What is more, industrial processing and distribution of fish from nearby culture ponds would greatly reduce the huges losses currently suffered in the marketing of smoked and sundried fish in Nigeria (Hayward, 1961; Mann, 1962; Awachie, 1975).
6.2 Effects of Fish Culture on Other Floodplain Projects
Culture ponds, as mentioned above, will be beneficial to other floodplain activities by providing among others a profitable means for the disposal of agricultural wastes and also cheap raw material (fish) for nearby industries. In addition, increased quantity of water in natural lakes, ponds etc. made available by erecting cheap dwarf earth dams across inlet/outlet channels will aid in livestock and industrial watering procedures.
Undesirable adverse effects of culture farms include the reduction of the number of pools, ponds, lakes and lagoons available for the traditional dry season pool fisheries. The rich areas available for flood fisheries would also be diminished. The overall effect will be to reduce the annual yield of capture fisheries. Added to the above is the possible and often inevitable competition of fish culture with arable crops for water which so far in Nigeria often ends with fish culture on the losing side. As is discussed below, suitable management procedures would help to alleviate, if not offset, some of the problems indicated above.
The interactions between the proposed fish culture and existing as well as projected uses of floodplain indicate the need to develop overall and integrated management strategies inorder to optimize the exploitation of Niger-Benue floodplain land and water resources. In a country where animal protein is an expensive commodity and where the mean of the two available projections (Olayide, 1966; Eweka, 1973) for the national per capital demand for fish for the target years 1975, 1980 and 1985 are put at 15.25, 16.95 and 18.60 kg respectively, it is important to achieve a healthy balance between activities aimed at meeting the animal protein needs of Nigeria's teeming population and the drive to increase cash crop production. It is suggested that these management measures should include:
My thanks are due to many State, Federal and International fisheries personnel currently working on fisheries problems of the Niger-Benue and associated river systems for their cooperation and useful discussions, and to many local fishermen as well as my field assistants, without whom it would have been impossible to operate meaningfully.
May I also take this opportunity to record my indebtedness to the International Science Foundation of Sweden for their travel grant, which made it possible for me to present this paper at this FAO/CIFA Symposium at Accra, Ghana.
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Figure 1 Map of Nigeria showing the main floodplains of the Niger-Benue system
Portion of Lower Niger floodplain showing its extent and distribution of larger perennial lakes and swamps
Stretch of the Lower Niger from apex of the delta to Ida showing main features of topography. Note the fadama constriction around Onitsha and the expansion into a pond-rich triangle between the Niger and Anambra River
Figure 4 Section of the Niger floodplain from Onitsha to just below Kainji to compare the width and distribution of the larger fadama lakes
Figure 5 North Eastern State section of the Benue fadama showing narrower width and fewer large perennial lakes and ponds
Fig. 6 PERENNIAL AND SEASONAL LAKE RESOURCES IN THE NIGER/ANAMBRA FLOOD PLAINS
Figure 6 Details of the rich Niger floodplain around Onitsha showing projected fish culture production trial areas around Atani-Odekpe and Otuocha-Anam
Figure 7 Benue floodplain showing mapped fish culture projected production trial area around Ribadu-Kocciel and Gurin near the Cameroon frontier
Figure 8 Ndakalowu area, showing perennial floodplain lakes which are cut off because of Kainji dam. The future of these lakes and their possible contribution to cultural fisheries development are uncertain (from Mutter, 1972)
Figure 9 Tada area of the Niger fadama further downstream. The isolated natural lakes would become maximally utilized by putting them under culture if their water supply could be improved by canalisation (from Mutter, 1972)