Effects of invasive water hyacinth on fish diversity and abundance in the Lake Cluster of Pokhara Valley, Nepal

Abstract

Water hyacinth (Pontederia crassipes) invasion is a growing global issue which poses a threat to aquatic life. As in the global context, the water hyacinth invasion is increasing rapidly in the lakes of Pokhara valley which is listed in Ramsar sites. Its effect on aquatic life is little known. This study examined the effects of water hyacinth invasion on the diversity and abundance of fishes in lakes of Pokhara Valley. We estimated the seasonal fish diversity and abundance in water hyacinth presence (HP) and absence (HA) habitats between 2019 and 2020. The study found that water hyacinth invasion has a negative impact on fish diversity and abundance in the lakes of Pokhara Valley. Twenty fish species were recorded, with family Cyprinidae being the most abundant. Fish abundance was higher in the winter season and in habitats with water hyacinth presence. The invasive Oreochromis niloticus was the most abundant fish in both habitats, but more so in habitats with water hyacinth presence. The exotic fish species Ctenopharyngodon idella had greater abundance in habitats with water hyacinth presence while Ciprinus carpio had greater abundance in habitats without water hyacinth. Exotic fish species abundance was positively correlated with water hyacinth coverage. The findings suggest that water hyacinth invasion negatively impacts native fish species, with the diversity of native species being low in habitats with water hyacinth presence. The study recommends regular stock enhancement programs for native fish species, control and management of invasive weeds, and further study to support the conservation of native fisheries resources and the livelihood of the fishery-dependent community.

Keywords

• Exotic
• Invasion
• Native
• Physico-chemical
• Threatened
• Water hyacinth