Assessing effects of pond effluents on the diversity and abundance of Macroinvertebrates and Zooplankton along selected streams in Wakiso, Central Uganda

Abstract

Uganda is targeting 1,000,000 tonnes from aquaculture only by 2030 since fish farming is now looked at as a very good economic venture for feeding the estimated 50 million people. Wakiso District contains several fish farms practising pond culture and was shortlisted among the 31 districts in Uganda that were identified for fisheries and aquaculture development based on both natural and socio-economic factors. The economic venture pauses ecological threat on the streams that receive the pond effluents especially species of the aquatic organisms that are so sensitive to the changes in water parameters. The fluctuations in water parameters along streams have direct effects on the diversity and abundance of aquatic organisms especially the intolerant ones. Shannon index of macroinvertebrates sampled upstream (1.675) was higher than the index of macroinvertebrates sampled from downstream (1.557). the same diversity index showed that diversity of zooplankton was generally high upstream (2.386) and downstream (2.414), but lower in the ponds (2.344). There were significant variations in the means of three physico-chemical parameters; temperature, dissolved oxygen and PH (p<0.05) at the different sample points. However, mean conductivity showed no significant difference between the sample points (p>0.05). The abundance of macroinvertebrate populations was easily recognized at the order level, whereby Dipterans and Odonatans had higher abundance in the overall population. Aquatic insects in order Odonata can survive in low oxygen because they have a close tracheal system. This study has shown that pond effluents has relatively no effects on the downstream ecosystem as far as diversity and abundance of macroinvertebrates and zooplankton are concerned. Ecological effects of waste waters from fish farms require frequent research in order to protect environmental health. Aquaculture subsector in Uganda is intensifying very fast therefore waste management research is key in order to mimic the environmental effects that may occur.