Frogfish, family Antennariidae, belong to the order Lophiiformes which include the nightmare inducing Angler fish. Whilst much kinder to look upon, they are as strange and deadly in equal measure as their close relatives. Approximately 5-40cm in size, the frogfish is a master in the art of camouflage. Covered in spinules and papillae, their variety of shapes and builds are quite breathtaking. This aids in predator avoidance and, along with a specially adapted ‘lure’, can entice prey to their demise. Some species, on top of these adaptations, can also boast the ability to change colour and others are covered in organisms like algae, not dissimilar to some decorator crabs I talked about in my previous post.
Found in most of the tropical and subtropical environments, the largest density of frogfish can be found around Indonesia. Typically these fish spend their time on the ocean floor, amongst the rock and coral reefs around 100m deep, where their camouflage can allow them to blend into the background. There are some exceptions to this however; the brackish-water frogfish lives in the river mouth of brackish and freshwater rivers. The Sargassum frogfish is found in the floating clumps of sargassum (a type of brown seaweed) in the subtropical oceans.
Their appearance allows them to be excellent ambush predators on the reefs. One such part of this disguise is a special adapted dorsal fin ray, called an illicium, which has evolved to become a fishing rod like structure with an esca, or lure, on the end to attract their prey. This lure can take on many forms and can be used to distinguish between species with some looking like small fish, worms, or just lumps of tissue. Due to their job requirements, the esca does sometimes sustain damage but it can re-grow. When the prey has been lured within striking range, the frogfish’s mouth cavity is opened and rapidly enlarged, in some species up to 12x its original size, which creates a vacuum to suck in helpless prey, which are unable to react in time. The whole act takes 1/6000th of a second. Small organisms are not the only ones that should be wary of the frogfish. In some species the stomach can expand to swallow prey that are twice their size!
Frogfish have some other unusual adaptations. Whilst also scale-less, they do not possess a swim bladder which hinders their ability to swim. Movement comes in two forms. In most species, the pectoral and pelvic fins have been adapted to allow them to ‘walk’. In the sargassum species these fins have evolved to allow them to clasp the seaweed and crawl amongst it. The second form of movement comes in short jet propelled trips through the water. Water is sucked in through the mouth a forced out of small tube-like gill openings that exit behind the pectoral fins, pushing the fish through the water.
The last adaptation from these amazing animals is one that is more familiar. Some species can intake water to inflate themselves like pufferfish. Check out an astonishing video of a Frogfish having a meal, and some great clips of them moving about in their habitat.