ABSTRACT

The study was conducted to monitor the production of zooplankton in concrete ponds fertilized with plant- derived organic matter. It was carried out in the fish farm of Michael Okpara University of Agriculture, Umudike. Experimental units were 12m2 concrete ponds. The source of water was an oligotrophic perennial stream. The ponds were limed with 1kg agricultural lime(Ca(OH)2) until a neutral pH was achieved. At the commencement of the experiment, initial water sample was taken for analysis. The ponds were then fertilized with 13kg dried grass. They were allowed to stand for one week and samples of water were again taken for analysis. Twenty litres were also taken for the determination of zooplankton density and phytoplankton communities. This was repeated one- week later. At the beginning of the 3' week, another batch of 12kg of dried grass and 2kg of chicken droppings was added. Water sample was taken for zooplankton and phytoplankton density determination. At the first week after fertilization, Brachionus species dominated thezooplankton population. This was followed by copepod, cladocera, bivalve larvae in decreasing order of abundance. Peak densities of Brachionus of 356 individuals per litre was attained in the 2 week. Peak densities of copepod of 395 individuals per litre was attained in the 3 week. Peak densities of cladocerans of 74 individuals per litre was attained in the 3 week also. Total zooplankton densities followed largely the same pattern of variation. A peak was observed in week 3. Peak total densities of 821 individuals per litre was observed in the 3 week and declined thereafter. After the peak densities, there was a gradual decline towards the end of the experiment. In the initial water sample, Brachionus overwhelmly dominated the zooplankton up to about 63% but in later weeks, the zooplankton population had a more equitable distribution with Brachionus constituting less than 40%. There were significant differences (P<0.05) among the weeks except between weeks I and 2. The significance of these and the merit of fertilization with organic matter are discussed. Also in the initial water sample, the phytoplankton community was dominated by three groups with the order: Chlorophyceae>Cyanophyceae>Baccillophyceae. In later weeks beginning from the second week the order became Baccillophyceae> Cyanophyceae> Chlorophyceae.