Sri Lanka's secret loaches: Scientists uncover eight hidden lineages in the Island's Hill Country streams

A team of Sri Lankan evolutionary biologists has revealed that the island's humble mountain loaches-tiny fishes often overlooked beneath rushing streams-hold a far more remarkable story than previously imagined.

- BY IFHAM NIZAM

What were once thought to be just three species of the genus Schistura have now been shown to comprise at least eight distinct evolutionary lineages, each tracing its own ancient journey across the island.

Their findings, published by Hiranya Sudasinghe, Kumudu Wijesooriya, Tharindu Ranasinghe, Dr. Rohan Pethiyagoda and Prof. Madhava Meegaskumbura, provide a vivid picture of how Sri Lanka's wet-zone rivers, waterfalls, and mountain ranges shaped the diversification of freshwater life over millions of years.

Lead author Dr. Hiranya Sudasinghe, who examined more than 250 museum specimens and analysed DNA from over a hundred individuals, said the team was astonished by the island's loach diversity.

"We expected some population structure," Dr. Sudasinghe explained, "but discovering eight well-defined lineages-each tied closely to one or a few river basins-was beyond our expectations. It's a hidden radiation in our own backyard."

The study shows that Sri Lankan Schistura form a monophyletic group-meaning they all descended from a single ancestral population that colonised the island long ago via the ancient Palk Isthmus, the only land route that ever connected Sri Lanka to India.