Frogfish are unusual, short, stocky, well camouflaged fish, with no scales, ranging from 2.5 - 38 cm in length. They are always present, but rarely during Koh Lanta diving trips.
Their mouths point upward, and many species can change colour and are sometimes covered in short spines and other appendages to aid camouflage. A frogfish may also be covered with other organisms such as algae or hydrozoa.
Frogfish have three dorsal fins, however the front fin has evolved into a 'fishing rod' (illicium) tipped with a lure or bait (esca) which helps to lure prey. The esca ('lure') takes a different form in each species, which the illicium ('rod') often has striped markings. If lost, the esca can be regrown. In many species, the illicium and esca can be withdrawn into a depression between the second and third dorsal fins for protection when they are not needed.
Frogfish typically move slowly, prefering to clamber over the bottom on their arm-like pelvic and pectoral fins rather than swimming. Once the prey is spotted, they can walk slowly to approach, and once in range, they strike extremely fast, in as little as 6 milliseconds.