FISH COMPOSITION AND PRODUCTIVITY OF LOWER RIVER NIGER, AGENEBODE, NIGERIA

Abstract

Inland waterswhich are important sources of fish for food and economic security are gradually declining in productivity.Studies have shown that the fish production capacities of Nigeria’s inland water bodies such as Lower River Niger (LRN) are negatively impacted by habitat modifications and other anthropogenic activities. Restoration efforts for sustainable management of LRN require updated information on its fish resources composition and productivity which are currently limited. Therefore, fish resourcescomposition,distribution and productivity of LRN at Agenebodewere investigated.

The LRN(46.4km) wasstratified spatially into downstream, midstream and upstream zones based on hydrological features. Two stations per zone were randomly selected.Water, phytoplankton and zooplankton samples were collectedbimonthly from each station for 24 months covering wet (April to October) and dry (November to March) seasons. Fish samples were obtained monthly fromthe fishers’ catches. Water samples were analysedfor Temperature (oC), Total Suspended Solids (TSS, mg/l), Conductivity(µS/cm), Dissolved Oxygen (DO, mg/l) and Gross Primary Productivity(GPP, g/O2/m3/d) using standard procedures. Phytoplankton, Zooplankton and fish samples were identified to species level. Length – Weight relationship (LWR, b >3 or <3 – allometric; b = 3 – isometric) of most dominant species was assessed. Species diversity was determined using Shannon-Weiner (H), species evenness(E) and Dominance (1–D) indices. Potential Fish Yield (PFY) was estimated. Data were analysed using descriptive statistics, ANOVA and canonical correspondence at α0.05.

Temperature were 27.4±1.9 and 27.8±1.5, TSS 51.7±8.8; 69.9±23.8, Conductivity 43.6±4.5; 76.4±9.8, DO 4.3±0.4 and 6.1±10.0 and GPP 0.70.03; 1.10.3, for Downstream and Upstream, respectively.Temperature, varied from 25.3±1.8 to 27.5±1.5; TSS 43.1±6.1 to 89.7±17.6; Conductivity 58.7±6.5 to 60.3±6.1; DO 5.3±0.6 to 5.5±0.6and GPP 0.40.1 to 0.80.1 for wet and dry seasons, respectively. Six families of phytoplankton and nine of zooplankton were encountered. Bacillariophyta (44.0%) andcopepods(48.0%) werethe most abundant phytoplankton and zooplankton, respectively. A total of 1886 fish samples comprising 20 families, 30 genera and 45 species were identified. Cichlidae constituted highest fishsamples (18.1%), followed by Mochokidae (16.97%) and Alestidae (16.70%)while the least were Dasyatidae and Ichthyboridae (0.1% each).Oreochromisniloticus(11.3%), Synodontisclarias(10.4%) and Brycinus nurse (9.4%) dominated the catch. Significantly higher fish sampleswere encountered in dry season (1073) than wet season (813). All the species encountered showed allometric(b3) growth rate except Xenomystusnigri which was isometric (b = 3). The PFY was 565.7kg/ha. Fish diversity indices in wet season (H=3.2; E=0.6; 1-D=0.9) were higher than dry season (H=2.4; E=0.4; 1-D=0.9).Fish abundance was influenced by conductivity, pH, turbidity and GPP at 70.6% cumulative Eigen-values.

Lower River Niger at Agenebodehas rich ichthyofauna diversity dominated by members of family Cichlidae. Conductivity, pH, turbidity and gross primary productivity are major environmental factors that impacted fish composition and productivity in Lower River Niger.