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The family of frogfish (Antennariidae = antenna bearers) comprise 12 genera (Allenichthys, Antennarius, Antennatus, Echinophryne, Histiophryne, Histrio, Kuiterichthys, Lophiocharon, Nudiantennarius, Phyllophryne, Rhycherus, Tathicarpus) with 44 known species. In the central Peruvian coast we have the Roughjaw Frogfish ( Antennarius avalonis ).
Frogfishes are relatively small fishes, the largest is about 38cm ( A. ocellatus ), but there are quite a few small species around 5 to 10 cm large. Some species can be of many different colors , from black to red, orange, yellow, browns, white, purple, green, some even have patches of blue. The colors usually help them to mimicry their environment such as sponges, corals and algae.
Frogfish Terms
Frogfishes are small stocky globose fishes (5-40cm). Loose prickly skin, limb-like pectoral fins with an elbow-like joint, small round gill openings behind the fins, very large upward directed mouth. The third dorsal fin is greatly enlarged. First dorsal spine is modified into a moveable fishing rod or luring apparatus (illicium) tipped with a lure or bait (esca). The rod or stalk comes in different lengths and is sometimes striped
Esca and illicium
The shape of the lure is one of the main distinguishing marks. The lure often but not always mimics a small animal. The lures of some species are shaped like a worm, others like a shrimp or even like a small fish with eye-spot and appendages resembling fins. While using the lure the frogfish even imitates the way which that particular animal would move. Using mimicry to catch prey is called aggressive mimicry.
Camouflage
Camouflage is a way to mislead the sense organs like eyes, nose or tongue into perceiving something different. Most animals use camouflage to hide from possible predators (= protective resemblance). In contrast the frogfish signals to other animals, that it is a place of shelter (rock, sponge) or a grazing ground (if is looks like algae). Having perceived the frogfish as nothing threatening, these animals approach and then get eaten. This is called aggressive resemblance.
The frogfish is a master of camouflage. His body is often covered with spots, stripes, warts, skin flaps and filaments. The frogfish mimics substrate and structures like algae covered rocks or rubble, plants like sargassum weed or algae, and animals like tunicates, corals and sponges. For example the striped frogfish ( Antennarius striatus ) looks with the help of skin flaps and appendages just like the algae it is hiding in. Other frogfishes look like sponges, down to the openings they immitate with spots on their skin.
Changing Colors
Because of their camouflage frogfish are difficult to find and - because they assume various colors - even more difficult to identify. For a long time scientists identified differently colored frogfish as separate species. Individuals of the same species can look to us completely different. To compound the problem most frogfishes can change their color in a matter of days or weeks. They mimic some objects in their immediate vicinity such as sponges, rocks, corals, tunicates. If they move to darker surroundings their body will adapt and change to a darker color. You often find black frogfishes on black sponges or close to black tunicates and yellow frogfishes inside yellow sponges and the patterns on frogfish skin often resemble the openings (ostia) of sponges or the apertures of sea squirts. The aggressive mimicry and the feeding behavior of frogfishes are one of nature’s most highly evolved examples of "lie-in-wait" predation.
Locomotion
Frogfish don't swim very often; most of them lack a swim bladder (except the Sargassum frogfish ( Histrio histrio ). To cross small distances the frogfish may walk or actually gallop. It can also move very quickly by sucking in large quantities of water through the mouth and forcing it out through the tiny gill openings. This results in a jet-like very fast forward propulsion a few centimeters above the ground.
It is interesting to note that frogfishes have reversed the order of their breast fins and belly fins. The powerful rear feet are in fact its breast fins!
Mating Behavior
There are no means to differ the male and female frogfish, for example by coloration or size except by examining the gonads by dissection.
About 8 to 12 hours prior to spawning, the female begins to fill up with eggs (40'000 to 180'000 eggs). This proceeds at a rapid rate so that shortly before spawning she is so distended, it is hard for her to maintain her position on the bottom. She becomes buoyant (tail up as shown) and is followed around closely by the male. The male continues to nudge the female in the abdomen, and they move quickly to the surface, where spawning occurs.
Parenting ends with mating. The thousands of eggs are released as an epipelagic egg raft (or veil), that drifts for several days and then sinks to the bottom after the embryos hatch. The planktonic stage lasts probably 1 to 2 months. Juvenile frogfish look like smaller versions of their adult forms, but some show special defensive colors
A few frogfish species (mostly living in Australia) show special parental care for their eggs. For example Lophiocharon trisignatus has fewer but larger eggs than other frogfish species. The male attaches a cluster of eggs with a threadlike structure to the surface of his body and carries them around until they hatch. The eggs of Tetrabrachium ocellatum (Four-armed frogfish or Humpback anglerfish) are wrapped around the dorsal fins which are specially hooked. Since a lot of fish like to eat eggs, these eggs might enhance considerably the overall luring effect of a frogfish. One of the mating pair of Phyllophryne scortea and Echinophryne crassipina stays close to guard their eggs. Would-be predators lured into the range by the embryos are known to be eaten by the parent frogfish!
Probably it is very difficult for frogfishes to find a partner in the deep sea. That is why the deep-sea angler (Families Ceratiidae, Caulophrynidae, Photocorynidae, Linophrynidae and Melanocetidae) shows a very strange sexual dimorphism. The male specimen is very small and attaches itself to the body of the female. The teeth and the jaw recede and the blood circulating of the two animals become one. The male frogfish spends the rest of his life attached to the female.
Baby Frogfishes
The juvenile clown frogfish ( Antennarius maculatus ) and the juvenile giant frogfish ( Antennarius commerson ) are said to mimic a distasteful flatworm, complete with undulating dorsal fins to simulate the swimming worm. Frogfishes are not poisonous but sometimes inflate their body by swallowing water so they can't be swallowed due to its increased girth.
Juvenile frogfishes seem to lure more frequently than the adult frogfishes. Especially the larger frogfish species change the way they hunt while growing. Young frogfishes hide a lot (like the smaller frogfish species). Very large frogfishes ( Antennarius commerson , Antennarius multiocellatus ) stay at the same place for a long time when they are grown up, so you will find them there during several dives.
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 plentiful 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.
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 Antennarius 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 Antennarius commerson ) will lure more often above its head and might have a longish lure. A frogfish living hidden in crevices (for example Antennarius 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 ( Antennarius 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 ( Antennarius 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 ( Antennarius striatus ). This frogfish also enlarges his esca by 35% when actively luring.
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 or one that is nearly not discernable.
Because the esca acts as bait it is apparently highly susceptible to loss or damage by attacks or nibbling of potential prey as well as predators. Therefore some frogfish 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.
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).
Frogfish hunting: luring, opening mouth, engulf the prey
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.