A group of fish called stonefish have weaponised a bone in their faces so they can wield it like a switchblade.
In these fish, the lachrymal bone, under the eye, is spiny and can rotate 90 degrees so that it sticks out from the face. This unusual feature, named the lachrymal sabre, has been found in males and females in all 63 stonefish species looked at so far, suggesting it is probably present in all 134 species in the group.
William Leo Smith at the University of Kansas discovered the facial weapon when he dissected a pet waspfish that had died in his aquarium. 鈥淚 literally got an adrenaline rush through my body and got super excited,鈥� he says.
Advertisement
Smith thinks the lachrymal sabre is primarily a defence against predators, making it harder to get the stonefish in their mouths and damaging to bite down on. But there鈥檚 鈥渁 very strong possibility鈥� that they are also used in fights between rivals of the same species, he says.
Light sabre
The sabre actually fluoresces a different colour to the rest of the head in these species. 鈥淚t is a bit counterintuitive to highlight this feature when these fishes rely so much on camouflage,鈥� says Smith. Detecting fluorescence often requires visual filters in the eyes that not all predators have. 鈥淲e don鈥檛 have evidence yet, but they could be communicating somewhat secretly through this fluorescence.鈥�
Stonefish are found throughout the Pacific and Indian oceans. In addition to the switchblade, they have a huge array of defensive features, including camouflage and spines containing some of the world鈥檚 deadliest venoms. Nevertheless, they are eaten in many parts of east Asia.
Smith and his team studied hundreds of specimens, collecting fish from the pet fish trade as well as looking through fishing boat hauls on a trip to Taiwan. They also peformed a genetic analysis of the stonefish, leading to a revised tree of evolutionary relationships between the species.
[video_player id=鈥漃nIIIdgd鈥� access_level=鈥漞veryone鈥漖
Copeia
Read more:听Fish鈥檚 toothy grin is perfect for crunching up armoured prey
听
