Sunfish belong to the same group of fish as the pufferfish (Molidae
). Members of this group have small mouths with beak-like teeth. The body is short and tall and flattened from side to side. The most striking characteristic of this species is the apparent absence of a tail as this is reduced to a stiff, frill-like membrane. In most fish the tail fin is the main means of propulsion, however in the sunfish the dorsal and anal fins are modified to form long 'paddles' which move from side to side. The upper half and fins are dark blue or grey-brown and the underside is silvery-white. This is one of the largest open water fish growing to a maximum length of approximately 3m. This species resembles the slender sunfish (Ranzania laevis
) however this species is very rare in the seas around Britain and Ireland.