An international team of scientists has identified at least 11 species of fish suspected to have abilities to walk on the water. The cave angelfish was first seen walking on rocks in a Thailand cave four years ago and now scientists have identified nearly a dozen species of fish with the same abilities. The rare and blind cavefish known as Cryptotora thamicola were found on the basis on CT scans and a new evolutionary map of the hillstream loach family that includes the only living fish species caught in the act of walking. Fish That Can Walk Accidentally Discovered in Tasmania: One of the Rarest Fish in the World.
These species have more robust sacral rib connections between an area of cartilage. This supports their fins and the spinal column letting them walk out of the water with a tetrapod‐like lateral‐sequence. The discovery was made by researchers from the Florida Museum of Natural History, the New Jersey Institute of Technology, Louisiana State University and Maejo University in Thailand.
Cave angelfish (Photo Credits: Florida Museum of Natural History)
Biologist Zachary Randall, manager of the Florida Museum's imaging lab and one of the study's co-authors was quoted as saying, "Fishes don't usually have any connection between their spine and pelvic fin. But before, the idea was that the cave angelfish was totally unique. What's really cool about this paper is that it shows with high detail that robust pelvic girdles are more common than we thought in the hillstream loach family." Four New Species of Walking Sharks Discovered off Northern Australia and New Guinea Coasts (Watch Video)
The fish was seen climbing up rocks in a waterfall with a similar movement of a salamander. Other types of climbing fish, including the Hawaiian waterfall climbing gobies, use undulation or suction to move out of the water. Cryptotora thamicola, however, walks with a gait known as a 'diagonal-couplets lateral sequence,' which only tetrapods have, something that animals descended from the shared four-footed ancestor. Also, this salamander-like gait has been observed in 11 more species in the hillstream loach family.
Cryptotora thamicola (Photo Credits: Florida Museum of Natural History)
According to the research, there are more than 100 species of hillstream loach living throughout Southeast Asia and the cave angelfish has been the only one with walking abilities. The new study found out three variations of pelvic structure in this massive family. These species have a long, narrow rib that connects to the pelvic plate. The second group was found with a thicker and curved rib meeting the pelvic plate and the last had a robust crest rib connecting with the pelvic plate.
Out of the 29 species studied, 11 fell into the third category having similar qualities of that of the cave angelfish and provides creatures with walking abilities. Callie Crawford, the study’s corresponding author and PhD candidate at NJIT’s Department of Biological Sciences said, "The modified morphology of these Balitoridae, particularly the enlarged sacral rib connecting the pelvic plate to the vertebral column, is a big part of why studying this family is so exciting."
He said, "What we’ve discovered is three anatomical groupings that have major implications for the biomechanics of terrestrial locomotion of these loaches, and the relationships among these fishes suggest that the ability to adapt to fast-flowing rivers maybe what was passed on genetically, more than the specific morphology itself."