Turns out, Frogfish are even cooler than you thought!
Frogfish are one of those fish nearly all divers are drawn to (provided you can find them). They are weird animals: they look more like a sponge or lump of algae than a fish, they don’t bother swimming but walk across the bottom instead, they can gulp down prey larger than themselves, and they have what is basically a fishing rod stuck to their foreheads. New research has now found that they are even weirder than you already thought, something is up with the lures at the end of their “fishing rod”.
Frogfish come in all kinds of sizes and shapes and one species that stands out as special, even for a frogfish, is the Hairy Frogfish (Antennarius striatus). Ever popular with divers, the Hairy Frogfish usually has hair-like filaments growing over its body to better camouflage itself an environments with high algal growth. They are active predators, with a worm-like lure they will wave around to attract prey. As anyone who has ever been lucky enough to see them hunt will be able to tell you, this technique is pretty efficient. But there is more to it than meets the (naked) eye.
Things change when you go for a fluorescent night dive. Biofluorescence is a recently newly discovered phenomenon in fish, though it is well known in corals. Unlike bioluminescence (where light is produced by the fish), biofluorescence is passive and happens when light that hits an animal (as when using a blue dive torch) is reflected in a different colour. Doing fluo night dives on coral reefs feels like you’re in a 90’s rave and popped the wrong (or right?) kind of pills, with neon greens and reds flashing all over your retinas. Some fish, like lizardfish fluoresce, potentially to communicate with each other.
The body of the Hairy Frogfish does not join in these exuberant colour displays (it’s an ambush predator after all), but here is the interesting thing: its lure does! When looking at a Hairy Frogfish with fluo-diving equipment, you’ll notice only one thing, a brightly fluorescent worm-like creature moving up and down. This creature is nothing other than the lure of our frogfish, mimicking the fluorescence that is also seen in the free-swimming worms it pretends to be, attracting fish that can see the fluorescent worms/lure.
This is the first time it has been shown that biofluorescence might be used to attract prey. It remains to be tested if fluorescent lures indeed help Hairy Frogfish catch more prey, but it is a very exciting glimpse into unexplored hunting strategies in the ocean. It also makes you wonder about how much else is happening in the ocean we cannot see (yet)…
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