An investigation into ecological impacts of water hyacinth and papyrus on fish in river Nile at Namasagali, Kamuli district.

Abstract

A study was undertaken in the upper Victoria Nile at Namasagali, in Kamuli district with the aim of determining the impacts of water hyacinth and papyrus on fish ecology between March and April, 2019. In total 13 sites dominated by water hyacinth and papyrus were identified but eight were randomly selected for this study. Fish samples were collected using a panel of gillnets (1-5 inches) set at 17:00 hrs and retrieved at 8:00hrs. Identification and classification of fishes was done basing on, the morphological features with the aid of identification kits. A total of 13 fish species were encountered in the vegetated habitats in comparison to nine in the open water habitats. Haplochromine fishes dominated native fish species in all sampled habitats. Four of the invasive species i.e. Lates niloticus, Oreochromis miloticus, Tilapia zillii, and Oreochromis leucosticlus were encountered in this study. Water hyacinth revealed the highest species composition and diversity and abundance (in terms of numbers) while papyrus exhibited the highest relative abundance in terms of weight (g±SE). Haplochromines, O. niloticus and L. niloticus in open water and papyrus habitats exhibited a negative allometric growth pattern as compared to the isometric growth exhibited by fish in water hyacinth habitats except for O, niloticus. The fish in all sampled habitats showed a good condition. The differences in the species composition amongst the habitats could be attributed to factors such as depth differences, vegetation and substrate types, and varying influence of season and diurnal patterns. Water hyacinth seems to act as a sheltering and nursing area of small size fishes while papyrus may act as a breeding area. Thus fishing in these areas should be prohibited and clearing of papyrus plants for agriculture should be punishable.