Assessment of Exotic Ichthyofaunal Composition in Colombo’s Urban Wetlands, Sri Lanka (2018–2024)

Sri Lanka hosts a rich diversity of freshwater fish, with 139 species recorded, including 61 endemics. Colombo, located in the Southwestern province and serving as the country’s economic hub, has an interconnected network of wetlands of significant ecological value. It is the world's only wetland capital city. Given the rapid urban development in the region, this study evaluates the composition of exotic fish species in nine urban wetlands in Colombo from June 2018 to March 2024. The surveyed wetlands included Diyasaru Park (DP), Beddagana Wetland Park (BWP), Thalangama Lake (TL), Diyatha Uyana (DU), Nawala Weli Park (NWP), Heen Canal (HC), Kimbulawala Jogging Pathway (KJP), Bellanwila-Aththidiya Wetland (BAW), and Kotte Rampart Wetland Park (KRW). Fish samples were collected through hand netting and direct visual observation, and all species were identified to the species level. Across the study period, 12 exotic fish species were recorded: Betta splendens, Chitala ornata, Helostoma temminckii, Mayaheros urophthalmus, Oreochromis mossambicus, Oreochromis niloticus, Osphronemus gouramy, Poecilia reticulata, Pterygoplichthys multiradiatus, Tilapia buttikoferi, Trichogaster trichopterus, and Trichopodus pectoralis. The highest proportion of exotic species was found in DP (66.6%), followed by BAW (58.3%), HC (41.6%), and BWP (33.3%), with KRW and DU both at 25%. TL, KJP, and NWP had the lowest proportion (16.6%). Notably, KJP, BAW, HC, BWP, DP, and DU recorded the introduction of 100%, 57%, 40%, 25%, 25%, and 33.3% of exotic species, respectively, primarily due to the ornamental aquarium trade, either deliberately or unintentionally. TL, KRW, and NWP showed no such introductions. In addition, the study recorded 16 native fish species from seven families: Anabantidae, Applocheilidae, Bagridae, Channidae, Cyprinidae, Heteropneustidae, and Osphronemidae. These findings highlight the need for updated monitoring of ichthyofaunal diversity in Colombo’s urban wetlands, which are increasingly threatened by pollution and urbanization. Further research on the ichthyofaunal composition, breeding patterns, population density, and feeding behaviors in larger water bodies within these wetlands is crucial to assess the impact on native species.

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Primary Presenter: Gayathra Charuka Bandara Aldeniyagoda Gedara, University of Kelaniya (gayathra.bandara@imbrsea.eu)

Authors:

Gayathra Charuka Bandara Aldeniyagoda Gedara, University of Kelaniya  (gayathra.bandara@imbrsea.eu)

Mahesh Dhamsara, Department of Animal Science, University of Peradeniya  (methindhamahesh9@gmail.com)