Sunfish

Sunfish

Sunfish ┬ęPete Mills

Sunfish

Scientific name: Mola mola
The ocean sunfish is the second largest bony fish on the planet and visits UK seas during the summer months to feast on jellyfish.

Species information

Statistics

Length: up to 332.7cm Weight: up to 1,320kg

Conservation status

Listed as Vulnerable on the IUCN Red List, but on a regional scale they are data deficient (meaning we don't know enough about the population to judge their conservation status).

When to see

June to September

About

The ocean sunfish is an odd looking fish. It is huge, flat and circular - looking pretty much like a giant swimming head. Instead of a tail, it has a stiff fringe of skin (called a clavus), which it can move to act like a ship's rudder. It also has two small pectoral fins and an elongated dorsal fin and anal fin that look a bit like wings. Their scientific name of Mola means millstone in latin - and it's easy to see where it came from!

They are often spotted resting on their sides at the surface of the sea, supposedly basking in the sunshine - which is where its English name of sunfish comes from. It has been suggested that this basking behaviour is to help the sunfish raise its body temperature after diving down to cooler waters to feed. The fin at the surface can easily be mistaken for a shark, but once up close they are unmistakeable.

Sunfish feed on jellyfish and salps (as such they are known as jellivores!), as well as a wide range of other animals. Smaller sunfish have the most varied diet - when they're under one metre in length, around half of their diet is jellyfish and the other half is a mix of species that live on the seafloor, like crustaceans, molluscs, and even some fish.

Ocean sunfish have a wide range and are found across tropical and temperate waters; they have been noted across the length of the Atlantic from Iceland to Chile. In the UK, they're most commonly seen in summer months.

The ocean sunfish used to be considered the largest bony fish in the world, but recently scientists discovered that its close relative, the southern sunfish (Mola alexandrini), is actually larger! Both fish can reach a similar length, but the southern sunfish is thought to be much heavier, with one fish recorded weighing 2,300kg. Both of these fish belong to the Molidae family, which contains five species (Mola mola, Mola tecta, Mola alexandrini, Masturus lanceolatus, and Ranzania laevis).

How to identify

A giant grey fish that looks a lot like a swimming head. They are round, reasonably flat and have no noticeably tail - simply a frill of skin (the clavus). They have 2 long fins - the dorsal fin and the anal fin which they use like paddles to steer and wings to swim. These fins can sometimes be seen flapping at the surface.

Distribution

An increasingly common visitor to southern and western parts of the UK in summer months.

Did you know?

In most other languages, these docile giants are called moonfish - it is easy to see why!

How people can help

Report any sunfish sightings to your local Wildlife Trust. Although sunfish bycatch is not a huge issue in UK fisheries, much of the tuna we eat results in sunfish bycatch. You can help by choosing "Pole and Line" caught tuna - this is captured using fishing rods and has zero bycatch. It also helps create jobs for local people in developing countries. Where possible, choose skipjack tuna as it is fast growing and is classed of Least Concern on the IUCN Red list. If you spot a sunfish at sea, maintain a distance of 100m and put the engine into neutral if any closer to avoid propellor injury. The Wildlife Trusts are working with fishermen, researchers, politicians and local people towards a vision of 'Living Seas', where marine wildlife thrives. Do your bit for our Living Seas by supporting your local Wildlife Trust or checking out our Action Pages.