The Ghats–Sri Lanka Connection

Somewhere in the rocky hill streams of the Eastern Ghats, water drops over granite in a quiet cascade, pools beneath the shade of forest cover, and moves on toward the plains below. It looks, at first, like any other forest stream. Beneath the surface, it is holding onto something far older than the landscape around it.

By Karthickeyen K.S.

Estimated read time: 3–4 minutes

The Eastern Ghats run for more than 1,750 kilometres along India's eastern flank, cutting through Odisha, Andhra Pradesh, Telangana, and Tamil Nadu. The rock beneath them is staggeringly old — between 1 and 3 billion years, older than the Western Ghats several times over, and far older than the Himalayas, which are barely 50 million years old. That age, and the rivers that have spent it carving through the range, have split the Eastern Ghats into separate hill clusters, each with its own drainage, its own rainfall pattern, and — as it turns out — its own distinct fish communities that science is still working to fully document

A Different Kind of Hill Range

Most people picture Indian hill streams as the Western Ghats — that continuous wall of mountains on the west coast, drenched by the southwest monsoon and running with perennial rivers fed by some of the heaviest rainfall in the subcontinent. The Eastern Ghats are nothing like that. Fragmented by major rivers like the Godavari, Krishna, and Mahanadi, and caught between both the southwest and northeast monsoons rather than just one, they're built from some of the oldest rock on the planet — and their streams are more seasonal, more variable, and far more locally distinct. Each hill cluster sits in relative isolation, cut off from its neighbours by river valleys and open plains. That isolation, sustained over millions of years, has shaped stream conditions and fish distributions that researchers are still in the process of mapping.

A Stream That Changes Every Few Metres

Walk one of these streams and the character shifts constantly — a riffle of white water over granite boulders gives way to a deep green pool, which narrows into a rocky run, before opening into a slow sandy stretch edged with roots and leaf litter. Each zone holds something different.

In the open water, the Malabar danio (Devario malabaricus) schools near the surface, its blue-silver stripes catching the light, while the quieter dandia rasbora moves through the same space just as quickly. In the slower, shaded margins, the striped panchax sits just below the surface, barely moving — a patient hunter watching upward for anything that lands on the water.

Unlike the Western Ghats, where perennial rainfall keeps streams running all year, these streams breathe with the monsoon. The northeast monsoon is the trigger — when it arrives, water levels rise, temperatures drop, and the entire fish community switches on. Species that barely moved through the dry months suddenly begin breeding, feeding, and moving through the stream in ways a summer visitor would never witness.

The Ancient Connection

In the deeper pools downstream, a different cast of fish takes over — and these pools carry something the Western Ghats fish fauna largely does not: a direct connection to Sri Lanka. Several species found in these Eastern Ghats streams — among them the dwarf snakehead pictured above and the Malabar danio — also turn up in Sri Lanka. Not close relatives. The same species. Sri Lanka and peninsular India were once joined by a land bridge, and freshwater fish crossed while they still could, long before the sea rose and cut the connection off.

A compact predator that spends its days tucked under roots and dense vegetation, most active at dawn and dusk, turns out to be carrying a story that stretches back before the coastline itself took its current shape.

Read the full story

The complete feature — including the full range of species documented across these streams, and what the genetic evidence actually reveals about the Eastern Ghats–Sri Lanka connection — appears in the May 2026 issue of The Weekend Aquarist

 👉Buy this issue or subscribe to The Weekend Aquarist to experience the complete tribute.