3. FISH SPECIES DIVERSITY IN RIVERS, LAKES, AND RESERVOIRS OF NIGERIA

Welman (1948) identified 181 species of fish from the major river systems of Nigeria and Lake Chad including some estuarine and marine species which frequent the rivers. Banks et.al. (1965, in White E. ed., 1965) identified and described about 139 species of fish along the upper Niger within the then proposed Kainji Reservoir Basin. Reed et.al. (1967) also identified and described about 160 fish species within the then northern region of Nigeria. Since then, numerous studies both in Kainji and other man-made and natural lakes in Nigeria have led to the description of new species and identification of species described earlier by scientists associated with the Kainji Lake Research Project and the National Institute for Freshwater Fisheries Research.

For convenience of comparison, the species diversity analysis is presented here in three main categories:

1. Fish species diversity in major rivers

2. Fish species diversity in natural lakes, wetlands and their inflowing rivers

3. Fish species diversity in reservoirs.

Considering the fact that all natural lakes, wetlands and reservoirs are supplied with fish by their inflowing rivers, it is apparent therefore that the rivers would be characterized by a higher species diversity than either the natural lakes, wetlands or reservoirs, particularly along their middle courses with extensive flats and flood ponds.

The fish stocks in the rivers are generally replenished from their adjacent floodplains after each flood season during which the fish breed. In view of this, any natural or artificial phenomenon such as drought or dam construction, which disrupts the natural cycle of flooding is bound to affect fish species diversity both in lakes (natural or artificial) and in wetlands. In the following analysis, attempts will be made to interpret the variations in species diversity in the light of such natural or artificial impacts.

3.1. FISH SPECIES DIVERSITY IN THE MAJOR RIVERS OF NIGERIA

Table 3 gives a summary of fish species recorded in the major rivers of Nigeria. Welman's (1948) list of 181 species is not restricted to any single river system and should therefore be regarded as the first major attempt to produce a checklist of fish species for all Nigerian inland waters. The checklist for fishes of Northern Nigeria (Reed et.al. 1967) has a total of 161 species.

The checklist produced in White (1965) covers the upper Niger within the then proposed Kainji Lake Basin and lists about 145 species. Species in the Anambra, Kaduna and Sokoto/Rima, major tributaries of the Niger are low in diversity as would be expected with 23, 28 and 22 species respectively. Compared with the major investigations of Reed et.al. (1967) and White (1965) which were funded internationally, the duration and extent of investigations by national institutions are usually limited by inadequate funding. The same constraints also limited the investigations into the Cross River, and rivers Ogun and Oshun with 39, 23 and 23 species respectively. In most cases the identification of species was limited to genus.

In spite of these limitations, an estimated total of about 230 fish species have been recorded from the rivers of Nigeria. Other rivers, not recorded in the literature, include the Imo, Qua Iboe, Benin, Owena and Calabar, all emptying directly into the ocean.

Table 3. Fish species diversity in the major rivers of Nigeria.¹

¹ In this table, as also elsewhere in this document, scientific names are those given by the author. No attempt was made to update them except as indicated in footnotes. Ed.
² now Parachanna obscura
³ now P. africana
⁴ synonym of H. brevis
⁵ synonym of H. vittatus