Sri Lanka supports a diverse freshwater fishes, about 48% of which are endemic. Most of these endemic freshwater fish species occur m the lull country forested streams of the wet zone. There are sophisticated interactions between fish species in a fish community and. its envnoiiment for food, space and/or spawning. As evident from the biology of cyprinids in hill streams hi Sri Lanka, most of the endemic freshwater fish species tend to show well-defined niche segregation and ecological adaptations. Several anthropogenic activites such as deforestation, gem.mining and uncontrolled use of agrochemicals; pose significant threats to snivival of many endemic freshwater fish species hi Sri Lanka. Exploitation of endemic fish species from the wild for ornamental fish trade is also a major cause of decline of their populations. Further, accidental introduction of clown knife fish (Chitala ornatusi and cleaner fish iPtngoplichtlns inuliiradiatus), wlhcli poses threats to diversity of freshwater fishes hi Sri Lanka, is an indirect adverse effect of ornamental fish trade. Although some introductions of exotic fish species such as African ciclilids. most notably Oreochromis mossambicus and O. mioticm. have socio-economic benefits, effective strategies should be implemented to control transfer and introduction of aquatic organisms.