The bump-head sunfish is a pelagic fish that differs from other sunfish species by the rounded edge of its clavus, the posterior part of its body which lacks a traditional tail. Its prominent head gives it the name 'bump-head sunfish'.

As an adult, it can reach over 10 feet in length and weigh more than 4,400 pounds.

The bump-head sunfish is found in tropical and temperate oceans, particularly around Australia, New Zealand, Japan, Chile, South Africa and the Galápagos Islands.

In Indonesia, the bump-head sunfish can be encountered at the Gilli Mimpang dive site, also known as Batu Tiga, located southeast of Bali.

The bump-head sunfish mainly inhabits deep waters, with a maximum depth of 1,640 feet. It is often observed basking near the surface, a behavior that may help it warm up after diving in cold waters or attract seabirds to remove parasites.

The bump-head sunfish primarily feeds on jellyfish but also consumes salps, fish, crustaceans and mollusks.

The bump-head sunfish reproduces sexually with external fertilization. Eggs are released into open water and fertilized by males. Upon hatching, larvae are only a few millimeters long and develop through several stages before reaching adult size.

The bump-head sunfish is the heaviest living bony fish species, with a record weight of 6,049 pounds for the carcass of a specimen discovered near Faial Island in the Azores in 2021.

Australian waters are home to five sunfish species: the bump-head sunfish (Mola alexandrini), the hoodwinker sunfish (Mola tecta), the ocean sunfish (Mola mola), the slender sunfish (Ranzania laevis) and the point-tailed sunfish (Masturus lanceolatus).