Frogfish are some of the most bizarre and interesting fish that can be found in the ocean. That is a bold claim to fame with some of the weird looking fish out there!
In this article we will introduce you to the weird and wonderful fish that is the frogfish!
IN THIS ARTICLE
Classification and Appearance
The term “frogfish” is used to describe any species in the family Antennariidae. There are 49 species, distributed across two subfamilies and 14 genera.
The Antennariidae family is part of the Lophiiformes order, which contains all anglerfish species.
Individual Frogfish species can look very different in appearance, due to their camouflage. However, all frogfish species do have the same basic characteristics.
They are small and stocky; quite atypical for a fish as it is not streamlined in any way. This stocky body type suits the frogfish well however, as they don’t rely on swimming to catch prey or escape predators.
Instead, they use their fins to walk along the seafloor and rocky substrate. The pectoral and pelvic fins have become modified, almost resembling legs and being strong and able to carry them. The modified fins are also very useful in holding the frogfish inn position.
Frogfish can walk in one of two ways; the first is to alternate moving each pectoral fin forward and walking on the seafloor, not using the pelvic fins. The second is similar to a gallop, moving the pectoral fins forward simultaneously whilst pushing forward on the substrate with the pelvic fins, then drawing the pectoral fins back and pelvic fins forward for the next “leap”.
Frogfish can also move openly in the water column by propelling themselves with their caudal fin. Younger and smaller frogfish often use jet propulsion as well, drawing big gulps water in through their mouths and forcing it quickly out of the gills.
Frogfish have a large prognathous jaw, which can be extended beyond the body. This upturned mouth is quite distinctive and allows frogfish to swallow prey as large as itself.
Frogfish are often very brightly colored in order to hide in their coral reef home; many species are bright red, orange, and yellow. While they don’t have scales, frogfish have modified scales called dermal spinules covering their bodies to further aid in camouflage. These spinules can be very large, and along with skin flaps and fin filaments can give the fish a hairy appearance. The coloration of different individuals in the same species can be wildly different, and some species have the ability to change coloration.
Habitat and Distribution
Frogfish are widely distributed in tropical and subtropical regions. They are found in the Atlantic, Pacific, and Indian Oceans. As with most types of fish, their highest biodiversity is found in the Indo-Pacific region, specifically around Indonesia.
They are almost exclusively marine fish, although there is one exception, Antennarius biocellatus, the brackish frogfish, which ventures into river mouths in brackish to purely freshwater habitats.
Generally benthic fish, they use their strong fins as arms to hold themselves in place and wait for prey to come to them. They are found on coral and rock reefs up to around 330 feet (100 metres) deep. The sargassum frogfish, Histrio histrio, uses modified fins to cling to and climb in sargassum seaweed. As the seaweed drifts, the frogfish can sometimes be found as far north as Norway!
Frogfish Camouflage and Mimicry
Perhaps the most iconic thing about frogfish is their camouflage and the mimicry that they display.
Frogfish have a specialized lure on their dorsal fin, called an illicium. The first three spines of the dorsal fin make up the illicium, which is then topped by the lure, called an esca, which is different to each species. As coloration can be so varied even amongst the same species the illicium and esca are perhaps the best way of identifying frogfish species. The striated frogfish, for example, has an esca in the form of a white worm. A tasty treat for an unsuspecting fish!
Using a lure such as this to entice prey to them is called aggressive mimicry. This is absolutely fascinating, as they have evolved to mimic a possible food item of fish, which the frogfish will then eat.
When a fish moves close to a waiting frogfish, it will move the illicium and esca in a way to perfectly mimic what prey item it resembles. As the fish comes ever closer the frogfish won’t take its eyes off it, before slowly starting to stalk closer on its fins.
The coloration and camouflage that frogfish display allows them to hide perfectly amongst a coral reef backdrop. Bright colorations let the fish merge with sponges and coral to lie in wait for prey. Frogfish can also change coloration, which allows them to remain perfectly camouflaged in different environments, such as during coral bleaching events, when they will turn white.
Having strong, fleshy, arm-like fins allows them to hold themselves in place easily
Frogfish aren’t fussy eaters. It was thought that each species of frogfish will have a preferred prey, as illicium and esca are unique in each species. However there is no correlation between what the esca looks like and what frogfish consume.
Frogfish have a large prognathous mouth, which means that the lower jaw of the extends further forward than the upper jaw. This allows frogfish to swallow prey as large as themselves. Sometimes frogfish can even eat larger fish! They strike extremely quickly, catching prey in as little as 6 milliseconds.
In the wild frogfish will happily eat any fish or crustacean that comes near. This includes other frogfish! It is the same in the aquarium. They will not only eat any fish the same size or smaller, they will also eat any invertebrates as well.
Initially frogfish may need to be enticed to eat when first placed into a new aquarium. This can be done by feeding them live feeder shrimp. Once they have fed initially they can then be fed both frozen and fresh meaty seafood, along with a healthy amount of live food.
Frogfish shouldn’t be fed every day. In the natural environment they eat only sporadically, so feed your frogfish once every three days.
Aquarium Compatibility and Tank Mates
Frogfish will view anything they can fit into their mouths as a potential meal, so they shouldn’t be kept with anything that is the same size as themselves or smaller.
This includes any invertebrates that are also in the tank, so unfortunately frogfish aren’t reef compatible.
While you might think that as frogfish eat anything that moves they will be very aggressive. In fact, the opposite is true, and if you house aggressive fish with frogfish they can be bullied and become very stressed. If they are stressed they can stop eating.
So ideal tank mates are large peaceful fish that won’t be aggressive towards the frogfish.
The minimum aquarium size that frogfish need varies depending on the species of frogfish and the size that they can reach. For instance the Striated Angler grows to 8.5 inches long and needs a minimum tank size of 30 gallons, while the Wartskin Angler grows to 4 inches and needs a minimum of 20 gallons.
Frogfish need a temperature range between 72-78°F, a carbonate hardness of 8-12 dKH, a specific gravity of 1.020-1.025, and a pH range of 8.1-8.4. They don’t do well with temperature fluctuations, so a good aquarium heater and thermometer are needed to regulate temperature.
They also need very clean water, so a high quality protein skimmer is essential to remove dissolved organic pollutants. Frogfish are quite waste heavy, so a high capacity skimmer should be used. A good filter, such as a canister filter or HOB filter is needed to provide mechanical, chemical, and biological filtration and keep ammonia, nitrite, and nitrate concentrations at undetectable levels.
Keep an eye on water chemistry using a testing kit, and take immediate steps to rectify any imbalances. Large water changes of 25% should be undertaken every two weeks will help keeping water chemistry in check.
As frogfish camouflage themselves amongst the coral, sponges, and rocks of the coral reef, they need the same in the home aquarium. A healthy number of sponges, SPS coral, and LPS coral will help in making your frogfish feel comfortable. Try to avoid strong stinging corals, as they can harm the fish.
Hopefully this article has brought you round to the wonders of the weird and wonderful fish that are the frogfish!
Reproduction in frogfish is quite fascinating, and we have written an article on specifically that: Frogfish Reproduction.
They are fantastic fish which make a great addition to reef tank setups. They prefer having plenty of coral and sponges in the tank, but make sure not to house them with any fish or invertebrates that are the same size or smaller! Frogfish are gluttons that will happily eat anything they can fit into their large mouths.