A bizarre type of fish with bone-like appendages uses its limbs not only to scramble around, but also to “taste” the seabed to find buried prey, researchers have found.
Sea robins have six bone-like structures formed from modified fins and are known to use them to walk on the sea floor and even turn shells over in a hunt for prey.
Researchers have long suspected that their bones can also help the fish locate food in other ways, and now scientists in the US have published two studies that reveal the genes that give rise to the seals’ bones and also how such limbs are used.
Write in the journal Current Biologyreport the team how they placed individual seals in tanks containing water and sand. Buried under the sand were either clams, capsules containing clam extract, or capsules containing seawater.
The team found that a species known as Prionotus carolinus regularly turned up all the prey-related items but not the seawater capsules.
Further work revealed that nerves in the limbs of these fish fired when the bones were exposed to various food-related chemicals, such as amino acids, while the seals could detect buried capsules containing such substances.
The team found that the fish’s ability to detect clams decreased with the depth at which the molluscs were buried, as would be expected if the seals use their limbs to detect chemicals released by the prey.
In addition, the researchers found that the bones of these seals were covered with small bumps similar to those seen on a human tongue, and the bumps carried taste receptors. The researchers suggest that the buds may increase both touch and chemical sensitivity.
Dr Corey Allard, a co-author of the research from Harvard University, said: “It’s as if they reused some of the machinery used in taste, but in a very different way, and to create a quite another reason.”
The team found another species of sea robin known as Prionotus evolance didn’t burrow and couldn’t find buried prey, while the nerves in its legs didn’t respond to the same range of food-related chemicals, and its limbs weren’t covered in bumps.
By studying other species of sea robin, the team suggested that the creatures’ legs were initially used for locomotion, and that other traits – such as greater sensitivity and the ability to taste – emerged later in evolution.
Allard said seals can provide scientists with an opportunity to study how new body parts emerge during evolution and form new traits, as well as how brains develop and adapt to such changes.
He said: “These crazy little strange fish have a lot to tell us that we probably couldn’t learn from a more conventional research organism like a mouse.”
