Have you ever been lucky enough to see a frogfish? They don’t quite look like a lot of other fish we are used to seeing under the water. They have fins that are like legs and a face that always looks like it’s in shock and they even have jet propulsion! A firm favourite of a lot of divers and photographers, let’s look a bit closer at the fascinating frogfish.
Frogfish are any member of the family Antennariidae of which there are around 50 species. These fish are masters of disguise by using camouflage to hide from predators and prey. Found in shallow tropical and subtropical waters they tend to be small with the largest species growing up to 15”/38cm.
In appearance the frogfish are a little different to a typical fish shape. They have short round stocky bodies with small tails and big heads. Many have appendages on their bodies along with spots, blotches, warts and hairy growths that all help with their camouflage. They have different colours and textures, often appearing sponge-like and some species’ wavy appendages make them look like algae, one species even resembles an urchin. Some also have algae or other hydrozoa covering their bodies’ surface. Their skin pattern often develops to look exactly like the environment they are living in. They can even replicate the pores of sponges that they live on by displaying ocelli or eye spots, hence why it can be very hard to spot them as they just blend in so well. It is thought that all species have the ability to change colour like a chameleon but that for frogfish the change takes a much longer time, maybe up to a few weeks.
Frogfish tend to not move much and hide on the ocean floor waiting for prey to pass. They have pectoral fins that are modified so that they can use these ‘leg-like’ fins to walk around on the ocean floor.
They can also swim by using jet propulsion! They have tube-like gill openings that are found just behind the pectoral fins, these tubes face backwards and when the fish gulps water it is then forced out through these openings pushing the fish forward.
The lures are what make frogfish very special. Also known as anglerfish, they basically come equipped with their very own fishing rod!
Frogfish are a very efficient example of a species using aggressive mimicry. Aggressive mimicry is where a species uses something that resembles something else, or a harmless third party, to gain advantage over its prey. In this case it is where the aggressor, the frogfish, is mimicking the prey of its own intended prey in the form of its shrimp/worm/fish shaped lure.
The frogfish lure or esca is on the end of a rod called the illicium which is the modified first spine of the dorsal fin, and is situated above the mouth of the fish. Frogfish are carnivorous and the lures can be different shapes such as worms, shrimp or squid etc, depending on the species and what they eat. When prey comes near, the frogfish can move its illicium or fishing rod so that the esca or bait resembles movement of the animal it looks like. When the prey is close enough the frogfish will expand its mouth (mouth volume enlarges up to 12 times normal size!) causing pressure which instantly sucks the prey, along with water, into the mouth.
This is known to be the fastest prey engulfment on record as it can happen as fast as 6 milliseconds!
The water swallowed flows out through the gill openings and the esophagus closes using a special muscle to prevent the prey from escaping and digestive processing takes place. After a meal it is possible to see the prey that was swallowed moving around in the stomach of the frogfish.
Fun Fact: Frogfish can also expand their stomachs and so are able to swallow something that is nearly twice their own size! They are also known to eat members of their own species.