Frogfish Behavior - Print Version

Compiled from several pages about frogfish behavior (without illustrations and photos)
Characteristics - Colors and Shapes - Feeding Behavior - Reproduction / see also identification - range

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The frogfish

The family of frogfish (Antennariidae =antenna bearers) comprise 12 genera (Allenichthys, Antennarius, Antennatus, Echinophryne, Histiophryne, Histrio, Kuiterichthys, Lophiocharon, Nudiantennarius, Phyllophryne, Rhycherus, Tathicarpus) with 48 (53?) known species.

Frogfishes are relatively small fishes, the largest ist about 38cm (F. ocellatus), but there are quite a few small species around 5 to 10 cm large. Some species can be of many different colours, from black to red, orange, yellow, browns, white, purple, green, some even have patches of blue. The colours usually help them to mimicry their environment such as sponges, corals and algae.


Frogfish Terms

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 (not covered by plates), very large upward directed mouth. The pectoral fins are modified and look like feet, including small toes.

First dorsal spine is modified into a moveable fishing rod or luring apparatus (illicium) tipped with a fleshy lure or bait (esca). The rod or stalk comes in different lengths and is sometimes striped. The third dorsal fin is greatly enlarged.


Esca and illicium

The shape of the lure is one of the main distinguishing marks that will even help a layman to identify a frogfish. The lure often but not always mimics a small animal. The lures of some species (A. striatus or A. hispidus) are shaped like a worm, others (A. commerson or Ph. scortea) like a shrimp or even like a small fish with eye-spot and appendages resembling fins (A. maculatus). 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.


Tips: how to identify frogfishes

Frogfish are determined by looking at the length of the rod and the form of their lure, the dermal spinules, the number of their spines, the number of fin-rays and the position of the gill opening. It is also important if there are eye spots (ocellus) present or they are missing. The colors are so variable, that they don't help much in identifying frogfishes. Some of the more uncommon colors can be used though to prove or disprove a certain identification.

If you want to find out which species of frogfish you have found, you should look closely and memorize or take a photograph of the following characteristics:

1. Luring rod longer / the same length / shorter than the second dorsal spine?
2. Characteristics of the lure and bait?
3. Does the frogfish has ocelli (eye spots) or other special characteristics like warts, stripes and what is its color?
4. Where did you find the frogfish? What kind of habitat (sand, reef, seagrass) and in which geographic area?


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 (A. 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. A newly discovered frogfish species (Histiophryne psychedelica) has stripes are all over the body that look like the patterns found on stony corals or bryozoans.


Changing Colors

For a long time scientists identified differently colored frogfish as separate species. Modern ichthyologists now recognize 13, perhaps 14 genera and 48 (53?) living species worldwide. Colors are - with some exceptions - not much help in identifying frogfishes.

Because of their camouflage frogfish are difficult to find and - because they assume various colors - even more difficult to identify. 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 is one of natures most highly evolved example of "lie-in-wait" predation.

In an aquarium you might be able to observe, that a frogfish changes its color to blend in with its surroundings, taking the color of a sponge or a coral. S. Michael has described a black frogfish with orange spots which turned over a one-month period first brown and then yellow with black spots.

Some frogfish species like all the Antennatus sp.ecies don't change colors at all, only some individuals are slightly darker or lighter colored.


Locomotion

Frogfish don't swim very often, most of them lack a swim bladder (except the Sargassum frogfish Histrio histrio , Allenichthys glauerti, Kuiterichthys furcipilis and Phyllophryne scortea). But it can 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. In the newly discovered Histiophryne psychedelica those are more like a series of short hops, pushing off from the ground with its pelvic fins.

To cross small distances the frogfish may walk or actually gallop. 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! Most frogfishes sit motionless on sponges, but the hairy frogfish (Antennarius striatus) likes to walk around. In order to attract prey it is moving the lure around in front of its head while walking.


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 eaten.

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.

The frogfish sometimes also actively stalks prey, I have seen a frogfish (Antennarius striatus) 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.


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 Antennatus 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. A study in luring behavior by S. Michael also showed, that a frogfish can vary its angling technique. A coinbearing frogfish (Antennatus nummifer) he observed used three different luring patterns - lifting the lure and vibrating the esca, holding the lure still in front of the mouth and throwing the angel rapidly back and forward.

Frogfishes even lure in the dark. Although the lure and esca can not be seen during night, the potential prey can feel the vibrations which are transmitted through the water and attack what seems to be an incautious animal.

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 Antennatus 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. It seems to take about 4 to 6 months to fully regenerate a lure.

Sometimes a predator also catches a frogfish. As the photos below show, the frogfish is inflating its body by swallowing water, so it is quite difficult for the predator (here a lizardfish) to swallow it. The photographer Stephane Bailliez wrote: I stayed around for more than 30mins while the lizardfish was stuck with this annoying prey. It tried a couple of times to do a quick release / catch in order to rotate it and thus tried different angles.

There is a group of frogfish species, which have no or a much reduced lure. The newly (2008) discovered frogfish species Histiophryne psychedelica (Ambon Frogfish) seems to block off the entrance to holes or crevices and thus entraps its prey inside. It would be interesting to investigate if other nearly rodless frogfishes like Histiophryne bougainvilli or Histiophryne cryptacanthus also employ a similar behavior of predation.

Frogfishes also have a small small white skin flap just above the mouth. I have observed this flap on several frogfish species, it is not always very prominent, but mostly of a white color. I haven't found any references to it in literature. I think, this is probably an additional enticement for small animals to go near the mouth!

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. The lower jaw is lowered and the upper jaw is expanded. 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 itself. 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 other fishes noticing!


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.

The following photos show the courtship and spawning behavior of several species of frogfishes. About 8 to 12 hours prior to spawning, the female begins to fill up with eggs (40'000 to 180'000 eggs). The eggs measure around half a millimeter. 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. The frogfish may spawn several times over a few weeks.

Parenting ends with mating. The thousands of eggs are released encapsulated in a ribbon-like buoyant mass of mucus known as an epipelagic egg raft (gelatinous raft or mucous veil), that drifts for several days crossing large geographical distances and then sinks to the bottom after the embryos hatch. The planktonic stage lasts probably 1 to 2 months. Even small larvae of 5 to 10mm have a lure. Larvae are typically deep bodied and have a large head.

Juvenile frogfish look like smaller versions of their adult forms, but some show special defensive colors (see Baby Frogfishes).


Brood care

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 female attaches a cluster of eggs with a threadlike structure to the surface of his body and carries them around until they hatch. One of the mating pair of Phyllophryne scortea 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! Histiophryne cryptacanthus and H. bougainvilli hide the cluster of eggs in a pocket formed by the pectoral fin and the tail which is bent around.

Several courting males of Rhycherus filamentosus gather around the gravid female. Females lay about 5000 eggs in a large mass. The egg mass consists of numerous single-egg strings attached to a gel disc of about 30mm in diameter. The disc is laid first, the long strings of eggs, each on a long sticky double filament. As the male releases sperm, the female fans the eggs with the caudal fin and posterior sides, trying to spread them out into the back of the cave. During this process the male is expelled. Sticky threads entangle themselves with the surrounding growth on rocks. The female then covers the eggs completely with her side and guards them. The young hatch after about 30 days and settle in crevices at the bottom (personal observation of Rudie H. Kuiter).

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.

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, like a parasite.


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. I think there are also examples of distasteful nudibranchs that look similar. Other frogfish species (Antennarius hispidus, Antennarius striatus) are just specially well camouflaged and look like algae covered rocks or like a slug. Frogfishes are not poisonous but sometimes inflate their body by swallowing water so they can't be swallowed due to its increased girth.

I have observed, that the juvenile clown frogfish is luring by moving its second dorsal spine instead of its rod and lure. Other juvenile frogfishes seem to lure more frequently than the adult frogfishes. I think this is because they are too small to be mistaken by their prey for a sponge or a algae covered stone, so they have to be more active in luring. Their lure is also larger in comparison with their body size and if you have a magnifying glass or a macro camera you can see it quite well.

Especially the larger frogfish species change the way they hunt while growing. Young frogfishes hide a lot (like the smaller frogfish species). When they are grown up large frogfishes (Antennarius commerson, Antennarius multiocellatus) stay at the same place for a long time on exposed areas in the coral reef , so you will find them there during several dives.



. Copyright Teresa Zubi