The abundance of Pellonula leonensis in relation to location, photoperiod, depth, tide, season and gill net selectivity was studied from May 2001 to April, 2002 in the Lower Nun River, Niger Delta. Three sets of gill net with stretched mesh sizes of 8, 12 and 15 mm respectively were used each measuring 35 m in length and 3 m in depth having a surface area of 105 m 2. Abundance was least in September and highest in February and P. leonensis was more dominant in the convex area of the river and lowest in the concave section. There was no significant variation (P > 0.05) in abundance of P. leonensis with photoperiod, water depth, tide and season. There was gillnet selectivity with the medium mesh size (12 mm) gill net as more effective constituting 68.77% of the total catch of P. leonensis in the Lower Nun River.

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The Physicochemical parameters of St. Nicholas River were determined from October, 2020 to September, 2021. Three sampling stations were identified and used throughout the duration of the studies. They were Meinmokiri, Ebierewo-bugo and Egeinkiri sampling stations. The physicochemical parameters were measured in situ with Mercury in Glass Thermometer for Temperature, Hand held Digital Salinometer for (Model AR8012) for Salinity, pH meter (Model PH-009(1)) for pH, Digital conductivity tester (Model AR8011) for Conductivity, TDS meter (Model AR8012) for Total Dissolved Solid, Digital Water Velocity meter (Model PF LV550) for Water Velocity, Secchi Disk for Transparency, Digital Depth Founder (Model SD-5) for Water Depth and Dissolved Oxygen Meter (Model OM-51-10) for Dissolved Oxygen. The mean values of the Physicochemical parameters of water at the three sampling stations are temperature; 29.98±0.550C, Dissolved Oxygen DO; 11.89±0.33mg/L, Biochemical Oxygen Demand BOD; 2.06±0.26 mg/L, Salinity; 16.80±2.06 PPT, Conductivity; 27.54±3.03µS/cm, Total Dissolved Solids TDS; 9.44±0.50mg/L, pH; 7.41±0.14, Water Depth; 0.58±0.06m, Transparency; 27.27±0.03cm and Water Velocity; 54.79±5.71m3/s. These physicochemical parameters values are comparable with other water bodies in the Niger Delta indicating contaminated waters. The contamination was caused by anthropogenic activities in terms of parameters assessed, therefore mitigation should be put in place for biodiversity conservation and sustainability of the ecosystem.

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