Fish Community Structure in River Ossiomo, Niger Delta, Nigeria in Relation to Some Selected Environmental Variables

In the past decade, it has been reported that water quality of rivers are deteriorating increasingly. In this study we examined the state of River Ossiomo to assess the current health of the river for a period of 24 months from April 2019 to March 2020, then July 2020 to May 2021 in three well marked out stations. The study was to determine the relationship between environmental variables and fish species assemblage in the river. From the results of the physico-chemical variables, the mean values of pollution indicating physico-chemical variables such as sulphate (1.26+0.32mg/l) and total suspended solids (TSS) (5.53+1.89mg/l) were higher in station 2. On the other hand, pH (5.94+0.48), DO (8.64+1.57mg/l), turbidity (7.48+7.63NTU), TDS (29.64+14.65mg/l) and phosphate (0.43+0.31mg/l) mean values were highest in station 1. Conductivity (70.87+26.42µS/cm) and nitrate (0.49+0.34mg/l) mean values were highest in station 3. Further, dissolved oxygen (DO) was higher in station 1, the reference station. The analysis of variance (ANOVA), we performed for the physico-chemical variables revealed that temperature, conductivity, DO, total dissolved solids (TDS), alkalinity, TSS, sulphate, phosphate and nitrate were significantly different among the three stations sampled (P<0.05), while pH, BOD and turbidity were not significant among the three stations sampled (P>0.05). The result of the principal component analysis showed that conductivity was positively associated with station 3, and temperature, TDS and alkalinity were negatively associated with stations 1 and 2. A total of 2,324 fish individuals belonging to 29 taxa were recorded in the entire study period. Station 1 harbours more fish species (1018), followed by station 2 (809), and we recorded the lowest number of fish individuals in station 3 (497). Auchenoglanis occidentalis was the most preponderant fish species probably occasioned by its level of adaptation to prevailing environmental conditions in the study river. The least abundant fish species was Synodontis eupterus.The canonical correspondence analysis we used in visualizing the relationship between fish species and physico-chemical variables showed that fish taxa such as Distichodus brevipinni, Cteropoma kinsleyae, Tilapia zillii, Malapterarus electricus, Mormyrus engystoma, and Synodontis nigita that were positively associated with pollution indicating physico-chemical variables were suggested as indicators for monitoring riverine health in the Niger Delta area of Nigeria. We recommend that more detailed studies should be carried out in River Ossiomo to confirm this result. However, this study serves as a baseline study in the present study area.