Frogfish: The odd one out

Frogfish, a.k.a. anglerfish, are part of the weird and wide group of ambush predators (They got the look). Somehow frogfishes stand out turning them into the all-time favourites of divers and underwater photographers. Some call them ugly, we find them fascinating for many reasons. Frogfish: The odd one out, having brought the art of „blending in“ to a whole new level.

Frogfish can form out more pores (oscula) to serve their camouflage (like on the left) or have relatively smooth skin (like on the right).

In style: Anything goes

There are around 46 different species of frogfish around the world. As their colouration varies, some are hard to distinguish. Generally, frogfish are stocky with a big mouth and oddly shaped fins. Sizes vary from fingernail to football. Their chubby, high-backed, unstreamlined bodies are scaleless.

There isn’t one particular style or colour that unites them. Basically, anything goes as long as it serves their camouflage, usually a sponge or encrusted rock, but also soft corals or even seaweed (sargassum frogfish). They are masters of disguise, slowly changing their skin colour and texture to match their surroundings perfectly, even mimicking the oscula/pores of the sponges they often sit on or next to. Additionally, they cover themselves with other organisms such as algae or hydrozoa.

Painted and clown: Juvenile frogfishes photographed in Lembeh Indonesia.

Looking bad: Movement and camouflage

Frogfish lack a swim bladder. Found in most swimming fishes a swim bladder maintains buoyancy in a similar manner to a diver’s BCD. If they have to they can use jet propulsion (drinking themselves forward) as well as strokes of the caudal fin. For short distances, they use their pectoral and pelvic fins to walk over the ocean floor. All of these look either odd or clumsy.

As they don’t want to give away their camouflage, frogfishes typically just lay and wait for prey. However, they make small adjustments to their position with their fins. When they spot potential prey, they follow it with their eyes.

Different species of the frogfish have different lures (escae), which they wave in front of their mouth to attract prey. Some have lures that resemble shrimps, others fishes, worms or tiny squids. Recent research has shown the striated frogfish’s lure to be biofluorescent.
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As soon as it approaches roughly seven body lengths, the frogfish starts to use its rod (illicium) and lure (esca) to get the prey closer. The esca doesn’t only look like the preferred food of the prey it is also moved in the same fashion.

Painted frogfish with its lure (esca) on the rod (illicium) moving to attract prey – photographed at Lipah Beach (Bunutan, Bali, Indonesia)

Anglerfish ambush

This behaviour got them their name: anglerfish (Antennariidae). Frogfish live the definition of “aggressive mimicry”: “Self-concealment to fool prey organisms or the use of special appendages such as lures to bait prey.”

Then it strikes extremely fast, in as little as 6 milliseconds their mouth opens u to 12 times the size creating a strong sucking motion. Afterwards, they can close off the mouth without reducing the volume within. This is the most rapid engulfment of all vertebrates.

On the contrary, changing colour does take some time, over weeks they can adapt to new surroundings.

Where to meet them and how they reproduce

Frogfishes are found in almost all tropical and subtropical oceans and seas around the world, with the main exception of the Mediterranean Sea.

One group of frogfish has a relatively small number of large eggs that stay attached to the body during their development. The other group spawns a mass of small eggs that immediately floats away in ocean currents all by themselves.