Researchers from New Jersey Institute of Technology have reported the discovery of a bizarre fish in Thailand that features unique anatomical features not commonly seen in modern day fishes.
The cavefish Cryptotora thamicola belongs to a species of walking fish with the unique ability to walk and climb waterfalls similar to that seen in four-footed animals such as salamanders.
Although it isn't the only known "walking" fish, some other species merely evolved an ability to use their fins in a limb-like manner to squirm across mud or push off from coral.
What makes Thailand's blind cavefish different is that it is more advanced compared with other species. It uses robust-pelvic girdle, just like tetrapods, four-limbed vertebrates that include reptiles, mammals, birds, amphibians and even extinct species of fish, to climb.
Scientists said that Cryptotora thamicola is the only known living fish species that features such a developed gait.
"It possesses morphological features that have previously only been attributed to tetrapods," said NJIT assistant professor of biology Brooke Flammang.
"The pelvis and vertebral column of this fish allow it to support its body weight against gravity and provide large sites for muscle attachment for walking."
The researchers said that the find may shed more light on how the anatomy for land-walking evolved since tetrapods are known to have transitioned from being finned to limbed creatures.
Ancient intermediate fish species are believed to be the first tetrapods, which adapted four limbs and other anatomical features for walking as they move from sea to land.
These early land vertebrates evolved adaptations so they can efficiently move in a terrestrial habitat when they move out of the water. Their vertebrae, for instance, grew flanges, which help the spine hold itself when being pulled by the gravity. A pelvis also joined the hind limbs to the spine.
Just like the newly discovered cavefish, scientists think that the early tetrapods walked much like salamanders.
"The blind cavefish Cryptotora thamicola walks and climbs waterfalls with a salamander-like diagonal-couplets lateral sequence gait and has evolved a robust pelvic girdle that shares morphological features associated with terrestrial vertebrates," Flammang and colleagues wrote in their research published in the journal Scientific Reports on March 24.
"These findings are significant because they represent the first example of behavioural and morphological adaptation in an extant fish that converges on the tetrapodal walking behaviour and morphology."