Abstract
Reservoir fishes contribute significantly to freshwater fish resources in Nigeria. The composition, size variation and relative abundance of fishes in Opa reservoir, Southwest Nigeria, were investigated to establish the ecological balance of the various trophic groups of fishes in the reservoir. The study was carried out in view of recent reports on the decline in the quality and quantity of water in the aging reservoir. Fishes were collected from the reservoir monthly for twelve months using monofilament gill nets and wire cages. The fishes were identified to species level and the ecological balance of the fish community was calculated as a ratio of the forage to the carnivore groups by number and by weight. Data were subjected to statistical analysis using the Stata 13 software. 1915 fishes belonging to 17 species and 10 families were collected from the reservoir. The fish composition was dominated by the family cichlidae, with its 7 species accounting for 89.8% of the total catch. There were 2 species of clariidae, which made 6.2% of the total catch. The ecological balance of the fish community was 3.4 (by number) and 6.2 (by weight). The result obtained revealed that the fish community in the reservoir is ecologically balanced.Comparative analysis of the fish composition of the Opa reservoir with reports from other reservoirs in Southwest Nigeria showed that the reservoir has more fish species than most of the other reservoirs around. The study concludes that the reservoir still supports a rich, diverse and ecologically balanced fish community. It is recommended that the management of these fish resources should be key in the holistic management of the aging Opa reservoir.
Highlights
Man-made reservoirs are important habitats of freshwater fishes in Nigeria, as such their stability has effects on the aquatic biodiversity of the nation
The fishes were identified to species level and the ecological balance of the fish community was calculated as a ratio of the forage to the carnivore groups by number and by weight
The fish composition was dominated by the family cichlidae, with its 7 species accounting for 89.8% of the total catch
Summary
Man-made reservoirs are important habitats of freshwater fishes in Nigeria, as such their stability has effects on the aquatic biodiversity of the nation. Many of these reservoirs were impounded primarily for purposes apart from fisheries. The reservoirs are naturally inhabited by riverine fishes which get adapted to lacustrine life This secondary purpose is rarely considered in the management of these water bodies. Earlier work [2] reported that the water has low pH, low water transparency and high total dissolved solids These aging processes affect the morphological features of the reservoir, which affects the life forms supported by the reservoir. The result will be a useful contribution to the conservation management of freshwater fishes in Nigeria
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