A team of marine biologists from the University of Kansas and the Field Museum, Chicago has discovered a remarkable defensive system — ‘lachrymal saber’ — in a group of fish called stonefish. Their work is published in the journal Copeia.
“I don’t why this hasn’t been discovered before. It’s probably because there are just one or two people that ever worked on this group,” said Professor William Leo Smith, from the Biodiversity Institute and Natural History Museum at the University of Kansas.
“We took five or six families and were able to resolve the problems in their classifications. To have this really strong anatomical feature visible from the outside is really helpful.”
All specimens Professor Smith and co-authors examined feature a mechanism they dub a ‘lachrymal saber’ located on each cheek below the eye.
Moreover, genetic analysis of 113 morphological and 5,280 molecular characters for 63 species reveals stonefish possessing the lachrymal saber are closely related, producing a revised taxonomy of flatheads, scorpionfish, sea robins and stonefish.
The researchers found the switchblade-like devices in the cheeks of stonefish involve specialized modifications to several bones and muscles: the circumorbitals, maxilla and adductor mandibulae.
“To help the stonefish deploy the switchblade, an unusually large number of muscles and ligaments attach to bones comprising the lachrymal saber system compared with species outside the stonefish family,” they said.
“The switchblade only added to an already impressive array of defensive features that rank stonefish among the deadliest fishes in the ocean, including spikes, camouflages and some of the world’s most powerful venoms, which even could be fatal to an adult human being,” Professor Smith said.
“Of all the fishes I’ve studied, I haven’t yet been stung by any of these stonefish.”
“I’m just super paranoid. In some places they catch them for food — the big ones, they’re delicious — there is an aquaculture for larger ones in Indonesia. That’s mind-boggling to me. The venom breaks down in our digestive system. But people eat lots of venomous species all over the world, even in the U.S.”
According to the team, the lachrymal saber is most likely an additional defensive system in stonefish, to avoid predation.
“If you find pictures of these stonefish in the mouths of other things, the lachrymal saber is always locked out,” Professor Smith said.
“The main thing people know about these fishes is they’re venomous. Some people know them because they have these fingerlike appendages and drag themselves around like they’re playing the piano; the appendages actually taste food as they go.”
These stonefish can mimic leaves floating in the water — they’re super camouflaged.
“A lot of them have really bright pectoral fins on sides of their body, and when they’re scared they flash them — this drab fish will suddenly flash bright yellows and oranges,” the scientist said.
“I always assume all of these features are defensive, but recent studies by other fish scientists suggest these could all be displays like a peacock.”
W. Leo Smith et al. 2018. Phylogeny and Taxonomy of Flatheads, Scorpionfishes, Sea Robins, and Stonefishes (Percomorpha: Scorpaeniformes) and the Evolution of the Lachrymal Saber. Copeia 106 (1): 94-119; doi: 10.1643/CG-17-669