A bizarre type of fish with leg-like appendages uses its limbs not only to scurry around but also for “tasting” the sea floor to find buried prey, researchers have found.
Sea robins have six leg-like structures that are formed from modified fins and are known to use them to walk across the sea floor and even flip over shells in a hunt for prey.
Researchers have long suspected their legs could also help the fish to detect food in others ways, and now scientists in the US have released two studies revealing the genes that give rise to the sea robins’ legs and also how such limbs are used.
Writing in the journal Current Biology, the team report how they placed individual sea robins into tanks containing water and sand. Buried beneath the sand were either mussels, capsules containing mussel extract, or capsules containing seawater.
The team found that a species known as Prionotus carolinus regularly turned up all of the prey-related items but not the seawater capsules.
Further work revealed that nerves in the limbs of these fish fired when the legs were exposed to various food-related chemicals, such as amino acids, while the sea robins could locate buried capsules containing such substances.
The team found that the ability of the fish to locate mussels decreased with the depth at which the molluscs were buried, as would be expected if the sea robins were using their limbs to detect chemicals released by the prey.
In addition, the researchers found that the legs of these sea robins were covered in small bumps similar to those seen on a human tongue, and the bumps bore taste receptors. The researchers suggest that the bumps could boost both touch and chemical sensitivity.
Dr Corey Allard, a co-author of the research from Harvard University, said: “It’s like they’ve repurposed some of the machinery used in taste, but in a very different way, and for a very different reason.”
The team found another species of sea robin known as Prionotus evolans did not dig and failed to find buried prey, while the nerves in its legs did not respond to the same suite of food-related chemicals, and the limbs were not covered in bumps.
By studying other species of sea robin, the team suggested that the creatures’ legs were initially used for motion, and that other properties – such as greater sensitivity and ability to taste – cropped up later in evolution.
Allard said sea robins could offer scientists an opportunity to study how new body parts emerge during evolution and novel traits form, as well as how brains evolve and adapt to such changes.
He said: “These crazy little weird fish have a lot of things to tell us that we probably couldn’t learn from a more conventional research organism like a mouse.”
