The Gollum Snakehead fish possibly evolved at least 109 million years ago (when the last dinosaurs still roamed the world), after the Indian plate drifted away from the supercontinent of Gondwana.

A picture of the Gollum Snakehead fish Image courtesy: Ralf Britz
news Science Monday, October 12, 2020 - 16:31

With its long, scaly body and delicate, veil-like fins, the Gollum snakehead captured quite some attention when discovered last year in south India. Now, scientists have found that it is genetically distinct from other snakehead fish worldwide and sports so many unique features that it warrants its very own family, Aenigmachannidae.

This new family is also ancient. It possibly evolved at least 109 million years ago (when the last dinosaurs still roamed the world), after the Indian plate drifted away from the supercontinent of Gondwana. The Gollum snakehead could well be a living fossil

“Aenigmachanna is by far the most important freshwater fish to be discovered in the 30 years I have been a student of South Asian fishes,” commented scientist Rohan Pethiyagoda who studies snakeheads in Sri Lanka, and was not involved in the study published last week in Scientific Reports.

Snakeheads (or channids, family Channidae) are predatory freshwater dwellers. The genus Channa is native to Asia and the genus Parachanna to Africa. Unlike many fish, they can thrive in low-oxygen waters thanks to a special breathing organ (the suprabranchial chamber) that allows them to survive on swallowed air.

This, along with the care they shower on their babies (such as fiercely guarding their floating eggs and mouthbrooding), has made them a very successful group. Too successful, in some cases. In the United States, accidentally-introduced four-foot-long snakeheads have invaded ecosystems and now bear the ignominious status of “injurious wildlife”.

How the species was discovered

However, at just around 10 centimetres long, the Gollum snakehead is barely a threat. What it is likely to be, is threatened.

It is possibly highly restricted in distribution. Both the Gollum snakehead and its sister species, the Mahabali snakehead, are thought to dwell in underground freshwater aquifers connected to paddy fields and open wells (that are tapped for everyday water needs) in Kerala’s Western Ghats. More distributional and ecological information about the fish is lacking. After all, scientists discovered it only last year.

Scientists Ralf Britz (currently with Germany’s Senckenberg Natural History Collections Dresden) and Rajeev Raghavan of the Kerala University of Fisheries and Ocean Studies – who were part of the team that formally described the fish – were puzzled when they first laid eyes on the Gollum snakehead. It flaunted some odd features: a uniform, cinnamon brown and long, eel-like body, unlike other snakeheads. Though the team went on to classify the fish as a new species, under a new genus (Aenigmachanna), they retained it in the only existing family of snakeheads (Channidae). But questions still remained. Could the Gollum snakehead turn out to be entirely different from other snakeheads?

A sister lineage 

To find out, Britz, Raghavan and their colleagues deconstructed the body parts of the fish. They used a nano-CT scanner to take 3D photographs of its skeleton and internal organs and compared these with the features of 14 other closely-related species (including snakehead and ray-finned fishes).

Astonishingly, the Gollum snakehead differed in five of the six main features that define channids. The fish, for instance, does not sport long canine teeth nor a suprabranchial chamber as channids usually do. Its swim bladder – an internal gas-filled organ that helps bony fish stay afloat in water – is far shorter too. By plotting all these morphological differences (and similarities) between the 15 fish species, the team concluded that the Gollum snakehead – whose many features are far more “primitive” than other snakeheads – must have split from other snakeheads long before the Asian and African species that we see today came into being.

Genetic analyses (of gene fragments as well as whole mitochondrial genomes) also point to this pattern: that the Gollum snakehead forms a distinct “sister” lineage alongside other snakeheads and not with or under them.

The Gollum snakehead warranted its very own snakehead family, Aenigmachannidae.

“What makes it really special is that it has an unexpectedly large number of primitive characters in relation to Channidae,” wrote lead author Britz in an email to Mongabay-India. “In a sense, it is the platypus of the snakehead world. There is some justification for calling it a snakehead ‘living fossil’ and it is this unique combination of primitive characters and a few weird derived features that lead us to consider coming up with a new family for it.”

As old as dinosaurs?

While that is very exciting (it is uncommon to find a whole new family of fish), what is intriguing is the ancient story this new family tells. The team estimated the age of the family using fish fossils and simulation algorithms. It turns out that the Aenigmachannids split from other snakeheads at least around 109 million years ago. This takes us back to an era when only two supercontinents existed in the world.

A large part of what is now India, along with Madagascar – called the Indian plate – was part of the supercontinent Gondwana more than 120 million years ago. At 109 million years ago, the Indian plate had already broken away from Gondwana and begun drifting north towards Eurasia. To put this in perspective: only after the Indian plate collided with Eurasia around 55 million years later were the Himalayas formed.

The drifting landmass, therefore, was already home to Aenigmachannas (where it must have lived alongside some of the last dinosaurs), and isolation due to continental breakups probably gave rise to these unique, ancient fish.

Yet when intense volcanic activity may have killed even the mighty dinosaurs over the millions of years that followed, how did tiny Aenigmachannas survive? Their subterranean natures may have helped, says Pethiyagoda.

“It is in some ways a freshwater coelacanth,” says Pethiyagoda. “It also signals that new light needs to be shone on the other fishes of Kerala that seem to live in aquifers, such as Horaglanis and Kryptoglanis. Almost nothing is known of the origin of these species or their ecology.”

The recognition of Aenigmachannidae as a new family of bony fishes comes six years after the description of Kryptoglanidae, another unique family of freshwater fish endemic to Kerala, said Raghavan. “The presence of two unique endemic families of freshwater fishes in Kerala is unparalleled, and indicates the exceptional diversity and endemicity of fishes in this part of the world.”

This story was first published on Mongabay and has been republished with permission. The original article can be found here.

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