You probably already want to avoid stonefish due to their highly venomous nature, but now researchers have found another reason to keep clear of these dangerous fish – they pack switchblades on their face.
In a new paper published in the journal Copeia, marine biologists describe this hardcore defensive strategy that has gone unnoticed until now. Called a “lachrymal saber”, the discovery of facial spines that flick out at will also has implications for the relationship of different stonefish species, meaning scientists may have to rewrite the evolutionary tree.
The discovery actually originated back in 2003, when one of the researchers was dissecting a stonefish he had kept as a pet. While doing this, he noticed that underneath the eye, there was a modified bone that could flick out, with the underside of it interlocking with another piece of bone on the fish's face. The two work in effect like a ratchet, allowing the blade bone to lock into position at different angles. On further analysis, it became clear that it wasn’t just the bones that had been modified, but that the blades also had a whole host of muscles and ligaments attached to them too.
“There can’t be any other reason for those muscles and ligaments except to control this mechanism,” explains William Leo Smith, who made the discovery and is associate curator at the KU Biodiversity Institute and Natural History Museum, in a statement. “This whole group of fishes is called the ‘mail cheek fishes’ or Scorpaeniformes, where the bones under the eye attach to the gill skeleton. Because all these muscles are attached to the gill skeleton, it allows for all this force which causes the lachrymal saber to deploy.”
After uncovering what his pet stonefish was capable of, Smith then turned to other related species. As it turned out, the fish wasn’t alone, as they all had these hidden blades. “I don't know why this hasn't been discovered before,” says Smith. “It's probably because there are just one or two people that ever worked on this group.”
Rather than being a mechanism to fight with, the lachrymal saber is most probably a defensive system. If another, larger predator tries to gobble a stonefish, it will flip the spines out to make swallowing it tricky. However, it could also serve another function – one of display not unlike a peacock.