Zooplankton assessment of Iyikpesu river Aragba- Orogun, Delta state, Nigeria
The composition and abundance of zooplankton in Iyikpesu stream, Aragba- Orogun, Delta State, Nigeria with selected physico-chemical parameters were investigated from July to December 2011. The air temperature varied between 20 and 27.3 °C with a mean of 23 °C, water temperature 20– 26 ºC (23±3 ºC), depth 0.8–2.1 m (1.45±0.65 m), dissolved oxygen 4.4 – 7.0 (5.7±1.3) mg/L, biochemical oxygen demand 0.7–3.1(1.9±1.2) mg/L, pH 3.2–5.9 (4.6±1.3), nitrate 0.34–0.35 (5.84±1.52) mg/L and alkalinity 30.0–48.0 (39±9) mg CaCO3/L. All parameters were within permissible limits. Eighty– three (83) species of zooplankton belonging to five (5) taxonomic groups were identified. Rotifers contributed the highest number of taxa (36) followed by copepods (9), cladocera (3) and protozoa (3). Rotifers constituted 86% of the total zooplankton, water mites (13.3%), copepods (4.8%), cladocera (1.6 %) and protozoa had the least with 0.8%. Among the rotifers, the most common genera were Filina, Polyarthra, Lecane, Testudinella and Notholca. Five major factors influenced the zooplankton composition and abundance. Two classes; aquatic insect of the Beatidae and copepoda were influenced by season while the DO/water temperature and pH factors influenced the cladocerans and rotifers respectively. Iyikpesu zooplankton communities were abundant and to support aquacultural practices.
Key Words: Abundance, composition, diversity, factor analyses, physico-chemical
parameters and zooplankton community