There is a blind, walking cavefish native to Thailand that can climb up steep, slippery rocks in rapidly flowing water. This is possible because the cavefish has a pelvis bone that is remarkably similar to a four-legged land animal. These finding could help scientists to understand the transition from finned to limbed appendages that took place around 420 million years ago.
Over millions of years fish have adapted a number of different behaviours to move out of the water, but until now none of them have been described as being able to walk on land with a tetrapod-like gait. Tetrapods are all four-legged, land-living vertebrates, which range from frogs to eagles to humans.
The blind cavefish, known as Cryptotora thamicola, is from Tham Maelana and Tham Susa which are both located in northern Thailand, possesses morphological features that have previously only been attributed to tetrapods. Based on anecdotal evidence, researchers already knew that these cavefish were able to walk, but due to them being so rare to come across and their protected status, studies into their functional morphology have been limited. However, Brooke Flamming, from the New Jersey Institute of Technology, and his team were able to scan a 47 millimetre long Cryptotora thamicola using a computed micro-tomography scanner. Additionally the team conducted a kinematic analysis by observing and filming wild cavefish at Mae Lana cave, they carefully scooped two of them into a glass tank for 15 minutes of kinematic sequences recording.
From their tests, the team discovered that the cavefish actually climb fast flowing waterfalls with what the team described as a diagonal-couplets lateral sequence gait. The teams’ description of the cavefish’s movement in more detail, the semi-synchronous movement of the right fore-fin and left hind-fin is followed by the semi-synchronous movement of the left fore-fin and right hind-fin. The rotation of the chest and pelvic girdles, which are the paired bones where limbs attach, creates a standing wave of the body midline. The way the cavefish’s movement has been described makes it seems that it convergently evolved in a salamander-like way of walking.