Native to the waters of Thailand and Myanmar, the rare pink and eyeless cave angel fish (Cryptotora thamicola) possesses an evolutionary ability that scientists have found spectacular.
This waterfall climbing cave fish, like its name suggests, can "climb" because of its wing-like fins, which in turn grapples onto terrain and allows the cave fish to stick to the cave rock.
However, seeing fish move on land is not unusual. What scientists found unbelievable is that this blind cave fish has a special waddling "walk" -- similar to that of a salamander -- that helps it climb the dark cave's waterfall.
In fact, the cave angel fish takes steps, moves one of its fins in sync with its opposite back fin, and alternates in a diagonal two-step.
Lead researcher Brooke Flammang of New Jersey Institute of Technology (NJIT) said she has not seen anything quite like it before.
"Functionally, it makes perfect sense, but to see it in a fish is incredibly wild," said Flammang.
Because the cave fish is incredibly rare, Flammang and her colleagues won't be able to dissect it for study. About less than 2,000 cave angel fish adults exist in its own home, making the government fiercely protective of these marine animals, as Wired reported.
So instead of further endangering the species, Flammang teamed up with Thai ichthyologist Apinun Suvarnaraksha who got permission into the caves and captured the fish on film before sending them back to the wild.
Prior to this, Suvarnaraksha had no experience collecting kinematic data, so Flammang helped him out by sending explicit instructions. Suvarnaraksha would collect videos, upload them to Google Drive, and Flammang would receive them. She would give feedback, and their online exchange went on for a couple of months.
Suvarnaraksha also got permission to CT scan a museum specimen of cave angel fish. This gave them data to create a detailed 3D model of the species' skeleton, without harming it.
The question now is this: how does the cave angel fish manage this amazing feat?
It's all thanks to the fish's gigantic pelvis which is fused to its vertebral column. The pelvis, which Flammang said looks nothing like any normal fish pelvis, lets the cave angel fish push forces from its limb directly to its core.
Additionally, Flammang believes that this bizarre anatomy is a first for modern fish, even though it is common among terrestrial vertebrates.
Flammang and Suvarnaraksha's discovery, which is published in the journal Scientific Reports, sheds light on the evolution of tetrapods.
