ADDITIONAL INFORMATION ON FISH STOCKS AND FISHERIES OF LAKE KAINJI
(NIGERIA)

by

J.K. Balogun and M.O. Ibeun

National Institute for Freshwater Fisheries Research
P.M.B. 6006
NEW BUSSA, Nigeria

Map of Lake Kainji, Nigeria, with location map insert, showing the original path of the River Niger and the three basins

1. INTRODUCTION

The status of fisheries research and development previous to 1984 was extensively discussed by Ita (1984). Attention was focused on fish population dynamics in the river and the lake, food habits, fish yield, fisheries management and experimental pilot fishery development.

The objective of this present report is to provide an update on the status and development of fisheries research and development on the lake between 1984 and now. This report highlights reproductive biology, aquaculture development, review of fish taxonomy, aquatic weed studies, age and growth studies, and biometric studies.

2. BACKGROUND INFORMATION ON THE LAKE

2.1 THE LAKE ENVIRONMENT

Kainji Lake (See map opposite) lies in the savannah region between 9°30' and 10°35' N and between 4°20' and 4°40' E, and was formed after the closure of the River Niger in August 1968.

The lake has an area 1 270 km², being 25 km at its widest point and 137 km at its longest. It contains 13.97 km³ of water at its maximum level. Although the primary purpose of constructing the lake was the generation of hydro-electric power, the lake offered great opportunities for a variety of development projects, such as fisheries, irrigated agriculture and improved navigation on the Niger River.

Three basins can be distinguished in the Kainji Lake (See map opposite):

• Upper Basin

  The upper basin is the area where the River Niger enters the lake. This basin is characterized by steep banks and a narrow channel. It forms about 10% of the lake surface area, with an average depth of 8.0 m.

• The Middle Basin

  The middle basin forms the largest portion, consisting of about 70% of the lake surface area, with an average depth of 10.8 m. It is characterized by an extended flood plain which is seasonally exposed during the drawdown period. Most of the area was completely cleared of vegetation prior to the formation of the lake.

• The Lower Basin

  The lower basin is the deepest part of the lake, with an average depth of 18.5 m. It is characterized by steep banks and covers about 20% of the lake surface area. The southern tip of this basin nearest to the dam site was also cleared of vegetation before impoundment.

2.2 HYDROLOGY

Mean monthly water levels in 1984 are given in Figure 1 (See Section 4.1, below). The water level of the lake increases from August to December and decreases from March to July each year. Apart from the regular inflow of water from the River Niger, the reservoir experiences two major floods, namely the ‘white’ flood and the ‘black’ flood. The white flood, characterized by high turbidity, is a result of rainfall in the catchment area of the River Niger up to Mali, and it enters the lake in late August. The black flood, caused by rainfall at the source of the River Niger, in Guinea, enters the lake in November and is characterized by a high water transparency. Fluctuations in the annual inflow result in marked variations in surface area, depth and shoreline area.

3. BIOLOGICAL DATA FOR THE RIVER NIGER AND LAKE KAINJI

3.1 FISH SPECIES IN THE NIGER AND KAINJI LAKE

The pre-and post-impoundment fish species composition was exhaustively described by Ita (1984). The nomenclature of four species - namely Clarias lazera (Cuvier and Valenciennes), Tilapia nilotica (Linnaeus), Tilapia galilaea (Artedi), and Parophiocephalus obscurus (Gunther) have since been reviewed and re-named Clarias gariepinus, Oreochromis (Sarotherodon) niloticus, Sarotherodon galiliaeus and Channa obscura, respectively.

Two gill net surveys were carried out - in 1976 (Ita, 1978) and in 1984 (Balogun, 1986). Comparison of these two surveys reveals changes in species composition. In 1976, 58 species were recorded, while only 43 species were caught in 1984. The major difference between the catches in 1976 and 1984 was that the Cichlidae, ranking third in terms of abundance in 1976, dominated the catches in 1984. The Bagridae and Cyprinidae, which formed low catches in the gill nets during the early post-impoundment period (Lelek and El-Zarka, 1973; Lewis, 1974) and ranked sixth and fourth respectively in 1976, became more important in 1984, ranking second and fourth respectively.

Major changes in species composition and the relative importance of the fish species and families were observed after the impoundment of Lake Kainji. The Mormyridae and Citharinidae/Distichodontidae were abundant in the River Niger, but after the impoundment the Citharinidae/Distichodontidae dominated the catches in the first two years and thereafter decreased in number. The Mormyridae did not feature well after the impoundment and remained very low, whereas the Cichlidae, Cyprinidae and Bagridae, which formed low catches in the River Niger and shortly after the impoundment, have significantly increased in number. The Characidae, which featured prominently in the River Niger, became dominant shortly after the impoundment and continued to remain prominent after the lake became a ‘tilapia’ lake in 1984.

A comparison of percentage composition by number of fish families in the regular gill net sampling in the period 1970 to 1973 and 1984 to 1985 is shown in Table 1.

3.2 STANDING STOCK OF FISH

The standing stock of fish in Kainji Lake was reported extensively by Ita (1984). The percentage composition by number of fish families in the shore, surface and bottom samples in 1976 and 1984 (Table 2) revealed changes in the fish species composition. The Cichlidae dominated inshore areas in both years, but in the surface catches the Characidae and Schilbeidae dominated respectively in 1976 and 1984. In the bottom catches the Bagridae and Mochokidae dominated respectively in 1976 and 1984. The general fish family distribution in the major habitats of Lake Kainji (shore, surface and bottom) remained similar in 1976 and 1984. Fish were distributed in a ratio of 1: 1.7: 1.9 in 1984 at the bottom, surface and shore respectively, which confirmed that the littoral margin is the most productive area of the lake.

Table 1 Comparison of percentage composition by number of fish families in the regular gill nets between 1970 and 1973 and between 1984 and 1985

Note: Results for 1970–1973 were based on surface catches, while those for 1984–1985 were based on shore, surface and bottom catches

Table 2 Percentage composition by number of fish families in the shore, surface and bottom samples in 1976 and in 1984

1976

1984

Sources: For 1976 data - Ita, 1978; For 1984 data - Balogun, 1986.

Table 3 Percentage composition of fish by number in Lake Kainji gillnet catches in 1984 and their relative distribution in the shore, surface and bottom samples

Note: Estimated from 180 gillnet settings.

(Source: Balogun, 1984)

Analysis of the gillnet catches in 1984 (Table 3) revealed that the greatest number of fish was caught in the shore area. The Cichlidae and Centropomidae showed preference for the shore habitat, the Bagridae for the shore and bottom habitats and the Schilbeidae for the surface. All fish families except the Cyprinidae have successfully colonized all parts of the central basin of Kainji Lake (Balogun, 1986).

3.3 MORPHOLOGY AND HISTOLOGY OF FISH SPECIES

A literature search showed that there was a paucity of information on the morphology and histology of the alimentary tract of fish species in Lake Kainji. Between 1984 and 1988, a detailed study on the morphology and histology of the alimentary tract of Lates niloticus was carried out.

Four basic layers - the mucosa, submucosa, muscularis and serosa - were observed to vary in structure from one region to another along the alimentary tract. The mucosa showed varying degrees of depth of folding. The oesophagus had shallow and numerous folds; the stomach had larger and fewer folds; while the pyloric caeca and the intestines had masses of folds with reticulate patterns.

The mucosal epithelium showed distinct variation in form and structure throughout the length of the tract. The epithelial layer in the oesophagus, stomach, pyloric caeca and intestine consisted of columnar cells with numerous goblet cells in the oesophagus and abundant goblet cells in the intestine. In the stomach and pyloric caeca, goblet cells were absent.

The submucosa of the alimentary canal consisted of loose connective tissue, blood and nerve cells. The muscularis was well developed throughout the tract. In the oesophagus, circular muscle fibres occupied the outer portion, with inner longitudinal muscles. In the stomach, pyloric caeca and intestines there were inner circular and outer longitudinal muscle layers. The serosa layer consisted of loose and thin connective tissue throughout the alimentary tract.

The folding along the tract serves for expansion and creation of a large surface area for secretion and absorption by the mucosa. Goblet cells produce mucin for lubricating the lumen and regulating the pH of the stomach.

3.4 AGE AND GROWTH STUDIES

Age determination in tropical fishes is a difficult problem due to poorly defined temperature changes and the availability of food throughout the year. Nevertheless, attempts have been made to determine the age of the Centropomidae, using various methods.

In Lake Kainji, a growth check was partly a result of low temperature and spawning in Lates niloticus (Balogun, 1988). Pre-and post-breeding feeding, increases in condition factor and low turbidity were also associated with scale ring formation in Alestes macrolepidotus (Balogun, 1982).

Application of the observed, back-calculated and Pauly's integrated methods would indicate that L. niloticus attain 10 years of age at 145 cm (T.L.) in Kainji Lake, and that the average values of maximum length (L∞) and the growth coefficient (K) are 162.6 cm and 0.2425 respectively for L. niloticus (Balogun, 1988).

Table 4 Comparison of some biological parameters and fecundity rates of some fish species in Lake Kainji

(Primary sources: Ita, 1984; Balogun, 1988)

Sources: (1) Arawomo, 1972;
(2) Balogun, 1988;
(3) Motwani, 1970;
(4) Willoughby, 1974;
(5) Ajayi, 1972;
(6) Akintunde, 1976;
(7) Olatune, 1977;
(8) Otobo, 1977.

3.5 REPRODUCTIVE BIOLOGY

The reproductive biology has been detailed for some of the commercially important fish families (Ajayi, 1972; Willoughby, 1974; Akintunde, 1976; Arawomo, 1976; Olatunde, 1977; Otobo, 1977; and Balogun, 1988). Sexual dimorphism and unequal sex ratios were reported in most fish families, including Cichlidae, Centropomidae, Characidae, Schilbeidae, Mochokidae and some Bagridae. The ratio of female to male in most fish families weighs in favour of the female, e.g., in the Centropomidae, Bagridae and Schilbeidae, while the ratio is in favour of the males in the Clupeidae and Bagridae.

The fish families fall into different spawning groups. The pelagic spawners include the Centropomidae, Clupeidae and some Malapteruridae, although most Malapteruridae are benthic spawners. The shoreline or swamp spawners include the Cichlidae and Bagridae.

Fecundity was observed to be a function of the size of the gonad, age of maturity, the egg diameter and the type of fish (Balogun, 1988). Fecundity varies from one fish family to the other (Table 4). Most fish families have fecundities ranging between 1 000 and 1 000 000, although a fecundity of over 30 million was recorded in the Centropomidae in Kainji Lake.

Most spawning in the lake occurs during the rainy season, May – October, in the Bagridae, Mochokidae and Schilbeidae. Some fish families, e.g., the Cichlidae and Clupeidae, spawn throughout the year, while other families, e.g., the Centropomidae and Malapteruridae, spawn during the flood season.

3.6 FISH PARASITES

The pre-impoundment survey of fish parasites showed that nematode, trematode, acanthocephala and cestode parasites were found in different fish species in the River, including in Oreochromis niloticus, Sarotherodon galilaeus, Synodontis spp., Bagrus spp., Gymnarchus niloticus, Citharinus citharus, Eutropius niloticus, Heterobranchus bidorsalis, Clarias gariepinus, Polypterus bichir, Mormyrus rume, M. macrophthalmus, Distichodus brevipinnis and D. rostratus (Ukoli, 1965).

The percentage of fish observed with helminthic infection was very low, and Ukoli (1965) predicted that the level would not constitute a threat to the productivity of future fisheries.

The post-impoundment survey of fish parasites by Akinpelu (1983) showed that trematode, cestode, nematode, and acanthocephala parasites were still present in various fish species. Trematodes were found in Oreochromis niloticus, Tilapia zillii, Sarotherodon galilaeus, Citharinus citharus, Bagrus bayad, Bagrus docmac and Synodontis membranaceous, while adult cestodarian infections were found in Synodontis gambiensis. Synodontis membranaceus, Clarotes laticeps and Eutropius niloticus harboured larval cestodes. Nematodes were observed in Alestes macrolepidotus, Distichodus brevipinnis, Distichodus rostratus, Bagrus bayad, Clarotes laticeps, Synodontis gambiensis, Eutropius niloticus and Lates niloticus, while acanthocephala were observed in Synodontis membranaceus, Oreochromis niloticus, Tilapia zillii, T. dageti, Sarotherodon galilaeus and Hemichromis fasciatus.

The prevalence of helminth parasites in the pre-and post-impoundment phases was highlighted by Okaeme (1991) who concluded that there was an increase in the level of incidence of parasites in the tilapias after the impoundment.

3.7 PRODUCTIVITY AND UTILIZATION OF MAJOR EMERGENT AQUATIC MACROPHYTES

Levels of productivity and utilization of emergent aquatic macrophytes in Kainji Lake have been reported (Service, 1969; Bacalbasa-Dobrovici, 1971; Chachu, 1978; Cook, 1965, 1968; Hall, 1975; Imevbore, 1975; Obot, 1984, 1985, 1986, 1987; and Obot and Morton, 1984).

The emergent aquatic macrophytes in the lake included Echinochloa spp., Cyperus sp., Pistia stratiotes and Ceratophyllum demersum, of which E. stagnina formed the major component.

In 1971, emergent macrophytes were estimated to cover only 0.5% of the lake surface area, but by 1977, 8.9% of the lake surface area was covered, in particular by E. stagnina (Obot, 1984). The macrophytes are most productive in the dry season, when the lake water level is highest, and are used as livestock fodder during the dry season.

The grass mat also serves as spawning and feeding ground for a variety of economically important fish species, especially the Cichlidae, Osteoglossidae and Centropomidae (Akintunde, 1976; Balogun, 1988; Obot, 1984). The aquatic emergent vegetation contributes to evapotranspirational losses from the lake and hampers small craft navigation.

3.8 AQUATIC BIRDS

A survey of aquatic birds associated with the Lake Kainji fisheries was undertaken by Okaeme et al. (1989). They found 74 species of aquatic birds associated with the lake. The birds were grouped into palaeo-arctic migrant, resident, vagrant, itinerant and intra-Nigerian migrant.

The study also revealed that the littoral zones and open water support most of the birds, with Sarotherodon galilaeus, Oreochromis niloticus and Chrysichthys nigrodigitatus forming part of their diet.

4. FISHERIES

4.1 FISHERY YIELD

The estimated total annual fish catch and the number of boats in Kainji Lake for the period 1969–1978 are given by Ita (1984). Ita (1984) also compared the mean catch rate per boat with the experimental catch per unit effort, and concluded that the lake had attained a natural equilibrium and that the catch was fluctuating between 6 000 and 4 500 t/yr.

There is an inverse relationship between the fish catches and water level in the lake (Balogun, 1986). The monthly fish catches (in % of total catches) in 1984 are shown in Figure 1, together with the water levels. When the lake water starts to recede in March, a gradual increase in fish catches commences and continues until August, when the lake water is at its lowest level. In late August, when the white flood enters the lake, the fish catches start to decline, and remain low from November to February, which is the period of highest water level.

4.2 PROCESSING, MARKETING AND DISTRIBUTION OF FISH

At the time of writing there was no organized processing of fish for commercial purposes, but increasing numbers of people were engaged in the processing, marketing and distribution of fish in the Kainji Lake Basin. In New Bussa alone, over 50 individuals were engaged in fish marketing and distribution.

The majority of fishermen own motorcycles to transport fresh fish to the fish-mongers in towns. The fishmongers own deep freeze units to store and preserve the fish for marketing.

Fishmongers in New Bussa transport fresh fish by car to reputable hotels in Kaduna, while the fishmongers that trade in smoked fish travel by public transport.

Improved fish processing, marketing and distribution have led to the percentage of fish that is smoked after landing decreasing to less than 80% of the catch.

4.2.1 Fish processing research on Lake Kainji

Fish processing methods in the Kainji Lake basin have been improved in order to provide a good quality fish product. The works of Eyo (1981, 1985, 1988); Eyo et al. (1988); Eyo and Asekome (1987); Eyo and Ita (1977); Eyo and Mohammed (1988); Eyo and Awoyemi (1988); and Awoyemi (1991) are all relevant in this context. Their main findings are summarized below.

Figure 1 The relationship between fish catch (in number) and water level in Lake Kainji in 1984

• Smoking kilns

  Two types of smoking kilns have been fabricated and tested. They proved very efficient in smoking fresh fish. These are Watanabe and Kainji Gas kilns. The Watanabe kiln was found to smoke fish better than the traditional kiln, which often burns the fish. The Kainji Gas Kiln is less labour intensive and can handle different sizes of fish faster, with better appearance of the end product. The kiln uses the commonly available liquid petroleum (cooking gas) for heat production. Smoke production is by smouldering sawdust and wood shavings instead of firewood. The Kainji Kiln is suitable for use in rural areas, where electricity is lacking.

• Smoking

  Of all woods tried for smoking, Detarium microcarpum, Parkia clappertoniana, Terminalia spp. and Daniellia oliveri were observed to impart the best colour and flavour to smoked fish. The use of oils, salts and insecticides (solution of actellicprimiplos-methyl) have been observed to have great potential in minimizing losses of stored smoked fish.

• Sun drying

  Sun-dried clupeid, Pellonula afzeliusi and Sierrathrissa leonensis, had high crude protein, ash, and lipid contents, with moderate calorific value and suitable minerals, including calcium, magnesium and potassium.

• Salting + sun drying

  Salted and sun-dried fish is generally free of fungi and insect infestation for up to six months.

  A salt content above 8–10% preserves stored fish samples from infestation by insects and mycoflora for up to 3 years.

• Ice-Storage

  Storage in ice was found to considerably extend the shelf life of the fish.

4.3 FISHERIES DEVELOPMENT AND MANAGEMENT

The absence of a systematic approach toward the development and management of the fisheries was reported by Ita (1982). For an optimum catch, only 1 920 fishermen ought to have been engaged in full-time fishing, against a total of 4 720 full-time fishermen on the lake.

Biological indices of overfishing in the lake were highlighted by Ita (1982). Proposals for a systematic management approach aimed at increasing the yield have been made (Ita 1982; Balogun, 1985).

A frame survey on Jebba Lake in 1984 revealed that 1 025 fishermen moved from Kainji Lake to Jebba for fishing (Table 5). From other surveys conducted earlier in Kainji Lake Basin (Bazigos, 1971, 1972; and Ekwemalor, 1975), it appeared that movement of fishermen with their boats started in 1973, and by 1975 over 200 boats (5.7%) had disappeared. Due to the advent of civilian administration in 1979, coupled with economic strangulation, fishermen have moved out of fisheries to join politics.

The experimental pilot fishery development project reported by Ita (1984) has since been discontinued due to non-adoption by policy makers.

4.4 AQUACULTURE

Cage and enclosure culture systems were introduced into Lake Kainji in the early 1980s (Otubusin and Opeloye, 1985). A cage culture experimental site was located at Shagunu on the western side of the central basin of Lake Kainji. The cage construction consisted of a module of floating net cages with bamboo rafts. The Dogongari Bay, a seasonally flooded enclosed bay located at the south-western side of Lake Kainji, was used for the enclosure culture trial. The impounded bay was blocked shore-to-shore with a mounted nylon net. The success of cage culture and its potential in the lake was earlier predicted by Konikoff (1975).

Table 5 Movement of fishermen from Kainji Lake basin to Jebba Lake basin (as of October 1984)

(Based on data supplied by the Statistics Section, Fisheries Division K.L.R.I., New Bussa, Nigeria)

Growth rates under extensive or semi-intensive systems were highest for Citharinus citharus, followed by Clarias gariepinus, Oreochromis niloticus, Sarotherodon galilaeus, Distichodus rostratus, Heterobranchus bidorsalis, Tilapia zilli and Alestes dentex (Otubusin and Opeloye, 1986). The enclosure culture system was found suitable for integration with poultry, cattle rearing and paddy rice cultivation (Otubusin and Opeloye 1986).

5. REFERENCES

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Akintunde, E.A. 1976. The biology of Tilapia and Sarotherodon species of Lake Kainji, Nigeria, with special reference to Sarotherodon galilaeus. M.Phil. thesis, submitted to Department of Zoology, University of Ife, Nigeria.

Akinpelu, A.I. 1983. Studies on the parasites of fish in Lake Kainji. MSc thesis, submitted to the Department of Zoology, University of Ibadan, Nigeria.

Arawomo, G.O. 1976. Food and feeding of three Citharinus species in Lake Kainji, Nigeria. J. Fish. Biol., 9: 3–10.

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