Urban stormwater ponds in Singapore: potential pathways for spread of alien freshwater fishes.
Urban stormwater ponds in Singapore are interspaced among the industrial and residential areas of this highly urbanized country and represent potentially harsh artificial habitats in which freshwater fish communities might be limited to low numbers of just a few hardy species. A recent first-time survey of three large urban ponds in Singapore, however, revealed that the fish communities in these ponds are greater in density and species richness than expected, with a combined richness of 24 species and fish densities ranging from 0.26 to 306.04 fish Ha-1. These fish communities consisted of only alien species, with the dominant species being Amphilophus citrinellus. The connectivity of urban stormwater ponds to other freshwater systems in Singapore, including protected catchments with natural stream and swamp habitats that are refuges for native species, could make these habitats hotspots and beachheads for the invasion or spread of alien freshwater fish. This is a cause for concern and raises the need for more stringent regulatory controls of fish releases into these ponds.