Fish Sampling: A fleet of gill nets consisting of nine multifilament nets of 25.4, 38.1, 50.8, 63.5, 76.2, 88.9, 101.6, 127.0 and 177.8 mm stretched meshes was used to sample shore, surface and bottom waters at the dam site. Each net measured 30m long and 3m deep, with 210/3 twine used for the first eight meshes and 210/6 for the 177.8 mm mesh.

Nets were set approximately 2 hours before sunset and lifted 2 hours after sunrise. The fish caught in each net were removed and transferred into large labeled plastic bowls. There was a separate bowl for each net. Each fish was weighed and measured for standard and total length. The forage to carnivore (F/C) ratios was estimated. The duration of survey lasted for four months i.e September, October 1997, January and July 1998.

RESULTS

The percentage composition of fish species/families by number and the relative distribution in the shore, surface and bottom waters are shown in Tables I and II. The most abundant fish family was the Cichlidae, followed in order of abundance by the families Cyprinidae, Schilbeidae, Mormyridae, Mochokidae, Characidae, Centropomidae and Bagridae. Along the shore the cichlids dominated while Cyprinidae dominated the surface followed closely by the  Schilbeidae. In the bottom the Cyprinidae also dominated. The Forage to Carnivore (F/C) Ratios were 1.17 and 2.28 in terms of number and weight respectively. The analysis of variance showing the variabilities of catches of various fish families among the major habitats (shore, surface and bottom waters) is shown in Table III. There was no significant difference in the overall catch composition among the major habitats. However the mean catches for the fish family Cichlidae were significantly different among the major habitats. A post hoc test was used for the mean separation test (Duncan Multiple Range Test) which revealed that the Cichlidae were highly concentrated in the shore waters. The fish families Bagridae and Centropomidae were caught only in the shore and bottom waters. The other families namely Mormyridae, Cyprinidae, Mochokidae, Characidae and Schilbeidae were caught from all habitats and showed no habitat preference.

DISCUSSION

The dominance of the fish family Cichlidae in Kangimi Reservoir compares favourably with other African lakes/reservoirs such as Kainji, Tiga, Bakolori where cichlids are known to dominate (Pike and Gay, 1965; Petr, 1966; Reynolds, 1973; Ita, 1978; Ita and Balogun, 1982 and Balogun, 1986).

The significant concentration of the cichlids along the inshore also indicates that the shoreline has been stabilized and is capable of providing enough food, shelter and breeding sites for the littorally-inhabiting fish species. Unlike the dominance of Sarotherodon galilaeus and Oreochromis niloticus in Lakes Kainji, Tiga and Bakolori, Hemichromis fasciatus dominated the cichlids in Kangimi. This could be attributed to differences in the feeding habits, behaviour and population. While O. niloticus and S. galilaeus are phytoplankton feeders, H. fasciatus are zooplankton feeders (Akintunde, 1976). The difference in feeding habit, behaviour and population affects rates of catches when different fishing gears are used (Ita, 1982). Other littoral inhabiting fish families include the Centropomidae and the Bagridae which were caught only in the shore and bottom water habitats. While the Centropomdae were caught more in the shore than in the bottom the Bagridae were evenly caught in the shore and bottom waters. The dominance of the surface by the Cyprinidae followed closely by the Schilbeidae was similar to situation in Kainji Lake.

Kangimi Reservoir fisheries differs from other African Reservoirs in the dominance of fish in the bottom habitat. In Kainji Reservoir the bottom water was dominated by the Mochokidae (Balogun, 1986) unlike the dominance of the Cyprinidae in the bottom waters of Kangimi Reservoir. The difference could be attributed to differences in the mean depth, flush rates and fishing rates in the reservoirs (Ita and Balogun, 1982). Though there was no significant difference in the total catch composition of all fish species among the major habitats the probability (0.06) was not well in excess of 0.05. The near significance level was reflected in the catch of individual fish family where the catch of fish family Cichlidae, the most dominant fish family showed significant difference (P < 0.05) among the major habitats with highest concentration in the inshore water. This result shows that the littoral zone is stabilized and conducive for the littoral inhabiting species.

The stabilization of the shoreline with the dominance of Cichlidae in the inshore, the dominance of the surface by the Cyprinidae followed closely by the Schilbeidae, the abundance of the Centropomidae and Bagridae and the Forage to Carnivore (F/C) Ratios of 1.17 and 2.28 in terms of number and weight respectively in the lake show that the dominant fish species are either primary or secondary consumers, thus indicating high potential to fish production under adequate management (Ita  and Balogun, 1982). For more efficient fisheries conservation and management, appropriate monitoring, control and surveillance (MCS) systems are required (FAO, 1995). Emphasis on MCS systems for inland water bodies are focused on registration of fishermen and their equipment, enactment of minimum mesh regulation and community based scheme (FAO, 1995). The absence of systematic approach towards the management and development of this reservoir is therefore advocated for fisheries sustainable yield.

CONCLUSION

This study reveals that Kangimi Reservoir is behaving like other African reservoirs/lakes where the cichlids dominate the overall catch composition. The study also reveals that the littoral zone is stabilized giving rise to the dominancy of littoral-inhabiting cichlids. However, the study shows that the common phytoplankton cichlid feeders which are dominant in other African water bodies are less prominent in Kangimi Reservoir where Hemichromis spp., zooplankton feeders dominates. The dominancy of primary and secondary consumers in the lake points to the high potential fish production of the reservoir under adequate management.

Acknowledgements: The fieldwork in this work was financed by a research grant from the National Agricultural Research Project (NARP) coordinated by National Institute for Freshwater Fisheries Research (NIFFR). The author is grateful to Mr. John A. Obemeata for the statistical analysis of the data.

REFERENCES