Community Spectrum, Seasonality and Diel Vertical Movements of Zooplankton in a Tropical Freshwater Fish Farm, South East Nigeria

Abstract

Zooplankton communities of Little Stream Farm, South-East Nigeria, were studied from March 2008 to February 2009 spanning a period of 12months. A total of 38 species belonging to 24 genera were identified. Rotifera were the most abundant with 16 species, followed by Cladocera with 9 species, while Copepoda and Protozoa recorded 8 species and 7 species respectively. The relative abundance of the different groups revealed 57.4% for Rotifera, 40.42% for Cladocera, while Copepods and protozoa contributed 3.36% and 2.30% respectively. Analysis of variance showed no significant difference (p > 0.05) in Taxa occurrence between the adjacent stream and the fish ponds, whereas a highly significant variation (p < 0.05) in species abundance was observed between the stations. Spatial distribution of organisms between the ponds indicated occurrence of larger individuals in the deeper layers indicating greater sinking rate of these size classes. Correlation coefficient (r = 0.817; p < 0.05) showed highly significant relationship between sinking rate and zooplankton size. Diurnal vertical movements of Calanoid Copepods related strongly (r = 0.924; p < 0.05) with corresponding movements of Cladocerans. A significant relationship (r = 0.879; p < 0.05) was also observed between zooplankton abundance and physico-chemical parameters.