The diversity and relative abundance of fish species in Sezibwa Riverine Wetland, Kayunga District, Uganda

Abstract

This study investigated the diversity and relative abundance of fish in Sezibwa wetland September 2005 and February 2006 in Kayunga District, Uganda. The main objective was to assess the diversity and relative abundance of fish species, based on representative habitats of the wetland at three sites; Bugonya and Ntenjeru sites in Kayonza Sub County and Gwero site in Galiraya Sub County in Kayunga District. Sampling for physico-chemical environments (pH, temperature and conductivity) was done using portable pH, temperature and conductivity meters and results recorded on site. Fish were sampled using experimental gillnets of mesh sizes one (1), two (2) and three (3) inches of 3 ply in thickness, hooks and conical traps. Fish samples were identified from keys (Greenwood, 1955; 1956; 1957; 1966) and referenced by museums specimens at Makerere University. Additional information was collected using questionnaires administered to people resident in the sampled areas. Direct observations and issues of interest to the research were recorded during the study. Results show that Sezibwa wetland has three main habitat types: the clear open water areas that appeared lacustrine without any vegetation; the open water areas with floating macrophytes such as the water lilies, Potamogeton, Ceratophyllum and water hyacinth (Eichhornia crassipes); and the sites that were fringed by emergent plants like papyrus, Cyperus papyrus, reeds Phragmites and, Typha species. The physical environments of the three habitats showed that the sites were different in their pH, temperature and conductivity. The highest pH was recorded in the clear open water habitats ranged from 6.59 to 6.86, while that of, open water areas with floating macrophytes was 6.13 to 6.78. The pH in habitats with fringing vegetation was 5.76 to 6.18. Water temperature range was 24.67 - 25.92 0C in the open water habitats, while habitats with floating water plants had a temperature range of 24.60 - 25.47 0C. The habitats with fringing vegetation recorded the lowest temperature that ranged between 23.95 0C and 24.87 0C. The water conductivity in open water habitats was 140.00 µS cm-1 - 184.00 µS cm-1 clear, while for habitats with floating vegetation it was 166.83 µS cm-1 to 196.50 µS cm-1, and recorded highest (174.2 µS cm-1 - 196.8 µS cm-1 ) in wetland habitats with papyrus, Phragmites and Typha plants. From the experimental sampling 11 fish species were recorded; Tilapia zillii, Oreochromis esculentus, O. leucostictus, O. niloticus, Protopterus aethiopicus, Clarias gariepinus, C. carsoni, C. alluaudi, Gnathonemus victoriae, Haplochromis and Ctenopoma murei. Another 8 fish species were reported by fishermen of Sezibwa wetland and these are; Synodontis victoriae, Mormyrus kannume, Labeo victorianus, Gnathonemus longibarbis, Bagrus docmac, Barbus altinalis, Ratrineobola argentea and Aplocheilichthys pumilus. The number of fish species recorded during the study was 19, belonging to nine families namely CICHILIDAE, BAGRIDAE, CLARIIDAE, LEPIDOSIRENIDAE, MORMYRIDAE, MOCHOCIDAE, CYPRINIDAE, CYPRINODONTIDAE and ANABANTIDAE. This implies that the Sezibwa wetlands and its environments has the capacity to accommodate a rich diversity of fish Bugonya and Gwero sites showed the highest diversity as indicated by the Shannon-Wiener index. It should be noted that small fish types which could not get into the experimental nets and not caught by fishermen for commercial purposes were not part of this investigation. It is also expected that depending on the physical environments which may includes seasonal changes in the amount of water in the wetlands, the observed fish species could be found at all sites. The diversity and abundance of fish in Sezibwa wetlands was observed to directly support people’s livelihoods in providing them with a cheap source of protein and jobs. Ecologically the wetland serves to buffer the catchment of the terrestrial areas of Mukono and Lake Kyoga in central Uganda and is an important breeding ground for fish in addition to providing habitat for other organisms which include plants, invertebrates, amphibian mammals and a diverse group of water birds.