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Aggressive Mimicry
The most interesting aspect of the frogfish, apart from his prefect camouflage is the way he attracts his prey. Other fish lie in wait until the prey swims close to their mouth (lie-in-wait predation), but the frogfish (or anglerfish) lures the prey (fish, crustaceans) actively to where it can strike. The lure mimics food animals like worms, small shrimps or small fish. The prey approaches to catch the lure and then is engulfed by the waiting frogfish. This strategy is called aggressive mimicry.
Of course not all prey is attracted by the lure. A more passive approach is the excellent camouflage of the frogfishes. Many animals just mistake a frogfish for a sponge, come too close and are swallowed. I have actually seen on various occasions, how small gobies flittered over the body of a frogfish sitting in a sponge, without being aware of the danger of getting swallowed.
Other fishes will perceive the camouflaged frogfish as perfect shelter and approach too close. Frogfishes often look like algae covered rocks. In coral reefs there isn't really a plenty full supply of algae for herbivore fishes. These fishes will approach a frogfish because they perceive a good feeding ground and are then caught. Because no herbivore fishes can eat plants surrounding the frogfish (they all get caught) these plants will grow extensively and even more fishes are attracted to the ambush site.
The frogfish sometimes also actively stalks prey, I have seen a frogfish trying to catch a small flounder by slowly sneaking towards it. It was trying to get the flounder into striking distance. The strike zone is about one frogfish body length.
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Luring prey
Frogfishes mainly eat fishes and crustaceans (shrimps and crabs). They can swallow items of prey that are twice as large as them. Luring techniques vary depending on the surrounding the frogfish lives in. A frogfish (for example A. striatus) living mainly on sand often has a lure that reaches close to the ground, so it can move the lure at the entrances of burrows or entice benthic animals like flounders to come closer. A frogfish living exposed on sponges or corals (for example A. commerson) will lure more often above its head and might have a longish lure. A frogfish living hidden in crevices (for example A. nummifer) often is small and has a small lure, more like a white ball and will stretch it in front of its head or just above.
Each frogfish species moves the rod (illicium) with its lure (esca) in a special pattern to attract the attention of potential prey. For example the warty frogfish (A. maculatus) moves its lure in wavy lines either above the head or directly in front of the mouth close to the ground, the lure is doing a circle. The giant frogfish (A. commerson) is moving its lure up and down in jerky movements. The frogfish on the following photos all have long lures.
Frogfishes also employ a chemical attractant. This is of importance to frogfish that forage at night like the hairy frogfish (A. striatus). This frogfish also enlarges his esca by 35% when actively luring. The hairy frogfish on the following 9 photos (a juvenile, about 9cm large) was walking about and luring during about 10 minutes, checking out several goby burrows but with no success. During some time it stretched the lure out in front while walking, then again it was moving the lure over its head in complicated patterns. It was interesting to observe the lure, which made wavy movements, then again was rolled up and nearly hidden.
Small frogfishes often prefer shallow water and live hidden in crevices between corals and among rubble. Hiding in such a way they avoid being preyed on by larger fishes. Smaller frogfishes probably don't use their lures as much as larger frogfishes to attract prey. Several of these frogfishes have very small lures (like A. coccineus) or one that is nearly not discernable (like A. tuberosus). The following photos show frogfishes with short rods and small lures (a small white dot). The rod is stretched out in front and not moved much.
Because the esca acts as a bait it is apparently highly susceptible to loss or damage by attacks or nibbling of potential prey as well as predators. Therefore some frogfish (for example A. pauciradiatus or A. randalli) have a pocket-like aperture formed by the membrane between the second and third dorsal spine which is used to protect the esca. Frogfish can regenerate their lure but might undergo a time of fasting until completion.
The Deep-sea anglerfishes even have a glowing lure (bioluminescence produced by symbiotic bacteria) decorated with filaments or branches that also glow in the dark. These frogfish have a massive mouth and razor-sharp teeth. The lure can be four to five times longer than the fish itself and some anglerfishes of the family Linophrynidae (Leftvents) even have barbels on their chin that also generate light and look like a hanging basket.
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Gape and Suck
When feeding, the frogfish expand the oral cavity. They engulf their prey with a reflex that sucks it in by creating suction pressure inside the mouth (increase up to 12 times in volume by expansion of the oral cavity). This is the fastest "gape and suck" of any fish, it takes only a six-thousandths of a second, which is faster than a scorpionfish or a stonefish (15 msec).
They can actually catch a fish out of a school without the other fish noticing the disappearance. A frogfish will easily swallow prey that is larger than it is. It doesn't have teeth, because the prey is swallowed whole and not cut into pieces by the teeth.
The frogfish is sometimes seen, opening its mouth and yawning. But only on two occasions I have seen how a frogfish actually eats its prey. Actually everything happened so fast, that all I really saw was the shrimp in front of the frogfish and then the frogfish moved and the next thing I realized the shrimp was gone and the frogfish made swallowing movements. No wonder that the frogfish can eat fishes out of a school without the otter fishes noticing!
Credits to Copyright Teresa Zubi
