An international team of scientists has identified at least 11 species of fish suspected to have land-walking abilities.

The findings are based on CT scans and a new evolutionary map of the hillstream loach family, which includes the only living fish species caught in the act of walking: a rare, blind cavefish known as Cryptotora thamicola, or the cave angel fish. Pinpointing which species of hillstream loaches have walking capabilities can help scientists piece together how the first land-walking vertebrates might have come to be.

In a new study, researchers from the Florida Museum of Natural History, the New Jersey Institute of Technology, Louisiana State University and Maejo University in Thailand analyzed the bone structure of nearly 30 hillstream loach species, describing for the first time three categories of pelvic shapes. Based on the shape of the bone that connects some loaches’ spines to their pelvic fins, the team found that 10 other species of loach shared the cave angel fish’s unusually hefty pelvic girdle.

«Fishes don’t usually have any connection between their spine and pelvic fin,» said biologist Zachary Randall, manager of the Florida Museum’s imaging lab and one of the study’s co-authors. «But before, the idea was that the cave angel fish 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.»

But not all loaches are so gifted: Though more than 100 species of hillstream loach are found throughout Southeast Asia, the cave angel fish is the only one whose walking capabilities have been observed and studied. Its salamander-like wiggle, powered by enlarged ribs bolstered with stabilizing muscle attachments, was first described in Scientific Reports in 2016 by Brooke Flammang, an assistant professor of biology at NJIT and the study’s lead principal investigator.

Randall said the cave angel fish’s walk is a key adaptation for surviving fast-flowing cave streams. It can grip rocky streambeds and move between habitats — even up waterfalls — as water levels fluctuate in the dry season. The cave angel fish’s increased mobility could help it access well-oxygenated stream regions with few or no occupants. Still, little is known about the species, including what it eats.

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Materials provided by Florida Museum of Natural History. Original written by Halle Marchese. Note: Content may be edited for style and length.