Amphibian biologist Rachunliu G Kamei was digging for legless amphibians called caecilians near a stream in the Khasi Hills when she came across a blood-red, snake-like creature with an elongated body and sightless black spots for eyes. “It is a unique adrenalin-rush excitement when you see a special animal like this in the field digging for hours [or days] in sweltering heat,” said Kamei when asked about her first thoughts on seeing the animal. “What struck me most was its bright color and the slenderness of the specimen.”
The elongated, hot pink creature was not a snake, or an amphibian, but a fish. It was a swamp eel, a group of fish that the authors call the “least fish-like” of bony fish. All swamp eels live in a dark habitat: either in stream beds and marshes, or underground, or in caves. Adaptation to a subterranean habitat means all swamp eels are blind. Their skin, which is never exposed to light, lacks pigment. Swamp eels have an extensive network of blood vessels just under the skin, meant to allow the swamp eels to breathe, giving the blood red colour.
Kamei and her colleagues from the Natural History Museum in London have called the new species Monopterus rongsaw. “Rongsaw” is the Khasi word for red – alluding to the blood red colour of the species in life. Swamp eels belong to the family Synbrachidae – a family of unique bony fish that lack eyes, fins and ribs and sport an elongated body. There are about 25 species of swamp eels across the world, found in all continents except Antarctica, said Britz.
M rongsaw was a serendipitous “by-catch”, said Kamei. “Since caecilian species [those in North East India] need water for reproduction, field work is generally done during the monsoon season [early May to late August],” she said. “I generally choose sites that are close to a water source [permanent/temporary] in a given locality [can be a forest, or agricultural areas], best generally is damp soil. And of course, these are sites you encounter swamp eels as well!”
Within the Indian subcontinent, swamp eels have been recorded from Kerala and in the North East. The enigmatic M rongsaw is very different from the other swamp eels found in North East India. Monopterus cuchia, a common swamp eel found in the rice fields of Assam, is actually cooked into a delicacy. The more widespread Ophisternon bengalense is a “brackish water mud-dwelling fish”, said Britz, found in river tidal zones of South and Southeast Asia, in areas like the Ganga delta. Monopterus ichthyophoides is known from one stream in Mizoram.