The Fishes of the Eastern Ghats that connect all the way to Sri Lanka
The Eastern Ghats run over 1,750 kilometres along India's eastern flank, through Odisha, Andhra Pradesh, Telangana, and Tamil Nadu. The rocks forming them are between 1 to 3 billion years old. In comparison, the Western Ghats formed around 65 to 150 million years ago and the Himalayas are barely 50 million years old. The rivers cutting through the Eastern Ghats have shaped separate hill clusters, each with its own drainages and rainfall patterns, and each carrying fish communities that science is still working to fully understand.
The Streams and Their Fish
Most people who know Indian hill streams know 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 a different kind of place entirely. Fragmented by major rivers such as the Godavari, Krishna, and Mahanadi, receiving both the southwest and northeast monsoons rather than one, and built from some of the oldest rock on the planet, these streams are more seasonal, more variable, and more locally distinct. Each hill cluster sits in relative isolation, separated by river valleys and open plains. That isolation, built over millions of years, has shaped stream conditions and fish species distribution that researchers are still in the process of documenting.
Image : An Eastern Ghats hillstream in Andhra Pradesh
The streams themselves shift character every few metres. A riffle of white water over granite boulders gives way to a deep green pool, which narrows into a rocky run, which opens 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, blue-silver stripes catching the light. The dandia rasbora (Rasbora dandia) moves through the same space, quieter in colour but equally quick. In the slower, shaded margins, the striped panchax (Aplocheilus lineatus) sits just below the surface barely moving, a patient surface hunter watching upward.
Image : Devario malabaricus (Malabar danio) in an Eastern Ghats hillstream
In the fastest sections, where water foams over boulders, the filament barb (Dawkinsia filamentosa) moves through the riffles, its bold black spot and red-tipped fins unmistakable. On the boulders beneath it, Garra species lock onto the rock surface using an adhesive disc under the mouth and graze algae while the current tears past them. Unlike the Western Ghats, where perennial rainfall keeps streams running all year, these streams breathe with the monsoon. The northeast monsoon is the biological trigger here. When it arrives, water levels rise, temperatures drop, and the entire fish community switches on. Species that barely moved through the dry months begin breeding, feeding, and moving through the stream in ways that a summer visitor would never see.
Image : Dawkinsia filamentosa (Filament barb) in an Eastern Ghats hillstream 
In the slower margins, the dwarf panchax (Aplocheilus parvus) represents one of the more remarkable biological strategies in these streams. Some killifish in this genus are annual fish, that is, they hatch when the monsoon arrives, mature within weeks, spawn their eggs into the substrate, and die when the water recedes with the dry season. The eggs lie buried in the mud through the heat of summer, and hatch again when the rains return the following year. The entire species exists as eggs for a portion of every year, surviving conditions that would kill most vertebrates. It is one of the more extraordinary life strategies found in any freshwater fish.
Image : Aplocheilus lineatus (Striped panchax) in an Eastern Ghats hillstream
In the deeper pools downstream, the ticto barb (Pethia ticto) schools in mid-water while the tank goby (Glossogobius giuris) sits motionless on sandy substrate below, mottled brown, almost invisible, waiting. The dwarf snakehead (Channa kelaartii) keeps to the margins under roots and dense vegetation, a compact predator most active at dawn and dusk. These pools also carry something the Western Ghats fish fauna largely does not, which is a direct connection to Sri Lanka
Image : Channa kelaartii (Dwarf snakehead) in an Eastern Ghats hillstream
The Ancient Connection
Several of these fish are also found in Sri Lanka like the dwarf snakehead, the filament barb, the Malabar danio, the dandia rasbora, the greenstripe barb (Bhava vittata), and the redside barb (Plesiopuntius bimaculatus). Not close relatives. The same species.
Sri Lanka and peninsular India were connected by a land bridge until the sea rose between them. Freshwater fish crossed while they still could. Scientists studying the dwarf snakehead genetically found that Eastern Ghats and Sri Lanka populations are nearly identical, shaped by a land connection that no longer exists. These streams predate the current map of the region entirely which is pretty amazing given the context of time.
Carrying the Story Forward
The Eastern Ghats fish fauna is among the least studied in India. The fish are there, in healthy streams, doing what they have been doing for millions of years. They just have not had many people appreciating.
The Eastern Ghats Ichthyology tee from da_starboi puts five of these species on your chest in a scientific field-guide illustration style. Native species, drawn with care, worn in public. These streams deserve a wider audience. Carrying their story is a small way to give them one.
Shop the Eastern Ghats Ichthyology Tee!
All images captured by Beta Mahatvaraj (Meenkaran)