# Ocean Sunfish — Facts, Threats & Conservation

*Mola mola (Linnaeus, 1758) — family Molidae*

> The ocean sunfish (Mola mola) is the heaviest bony fish alive at over two tonnes, has no true tail fin, feeds largely on gelatinous plankton, and grows to around 60 million times its larval weight.

**IUCN status:** Vulnerable — the heaviest bony fish alive  ·  **WARN range:** Temperate and tropical oceans worldwide, Open ocean, often near the surface

## Quick facts
| Fact | Value |
| --- | --- |
| Maximum weight | ~2,300 kg |
| Relatives | Pufferfish and triggerfish (Tetraodontiformes) |
| Tail | None — steers with a clavus |
| Buoyancy | No swim bladder; cartilage and gelatinous tissue instead |
| Dive depth | Several hundred metres |
| Main threat | Bycatch in drift and gill nets |

## Scientific classification
- **Kingdom:** Animalia
- **Phylum:** Chordata
- **Class:** Actinopterygii
- **Order:** Tetraodontiformes
- **Family:** Molidae
- **Genus:** Mola
- **Species:** Mola mola

## Conservation status
- **Status:** Vulnerable
- **Population:** Unknown
- **Trend:** Decreasing
- **Assessed:** 2015
- **CITES:** Not listed
- Sunfish are rarely targeted but form a very large share of the catch in some drift-net fisheries. Plastic ingestion is a documented cause of death.

## Key facts: Ocean Sunfish
- Ocean sunfish are the heaviest bony fish alive, exceeding two tonnes.
- They have no true tail fin — a rudder-like clavus takes its place.
- Larvae are a few millimetres long and covered in spines.
- They dive to several hundred metres and bask at the surface to rewarm.
- Bycatch in drift and gill nets is the principal threat.

## A body built by subtraction
Sunfish lose the tail fin during development. What remains is the clavus, a stiff rudder formed from modified fin rays, which the fish uses for steering while the tall dorsal and anal fins provide propulsion, sculled from side to side.

The skeleton is largely cartilage rather than heavy bone, and the body carries a thick layer of gelatinous tissue under the skin. That combination keeps a two-tonne animal buoyant without the swim bladder that most bony fish rely on.

## Basking, and why
Sunfish are often seen lying on their side at the surface, which produced the common name. This is thermoregulation: after diving into cold water at several hundred metres to feed, the fish returns to the surface to rewarm in sunlight.

The posture may serve a second purpose. Surface-basking sunfish are visited by seabirds that pick parasites off the skin, and the fish also visit cleaner-fish stations on reefs — a large animal with a heavy parasite load using two different cleaning services.

## Diet and the jellyfish problem
Sunfish were long described as feeding almost entirely on jellyfish. Better dietary studies show a broader diet including small fish, crustaceans, squid and salps, though gelatinous prey remains important.

That gelatinous preference creates a specific hazard: floating plastic bags closely resemble jellyfish, and sunfish ingest them. Plastic ingestion is a documented cause of death in the species.

## Why they are Vulnerable
Sunfish are rarely targeted commercially, but they are caught in enormous numbers as bycatch. In some drift-net and gill-net fisheries sunfish have made up a very large share of the total catch, and they are also taken in longlines.

They are listed as Vulnerable. Plastic ingestion, vessel strikes at the surface and the sheer scale of incidental capture are the pressures; targeted fishing is not.

## What WARN does
WARN publishes free, sourced species education for animals that decline through incidental capture and marine litter rather than deliberate hunting. Sunfish illustrate both at once — a species almost nobody fishes for, dying in nets set for something else and eating plastic mistaken for jellyfish.

If this guide helps you understand wildlife and the pressures it faces, a gift to WARN supports habitat protection and free public education in our partner countries.

## Frequently asked questions: Ocean Sunfish
### What is the heaviest bony fish?
The ocean sunfish, at over two tonnes. Larger fish exist — whale sharks and basking sharks — but those are cartilaginous, so the sunfish holds the record among bony fish.

### Why do sunfish lie on their side at the surface?
To rewarm. Sunfish dive to several hundred metres into cold water to feed, then return to the surface and bask in sunlight to raise their body temperature. Seabirds also pick parasites from basking sunfish, so the behaviour serves twice.

### Do sunfish only eat jellyfish?
No — that was the traditional description, but better dietary studies show a broader diet including small fish, crustaceans, squid and salps. Gelatinous prey is still important, which is why floating plastic bags are dangerous to them.

### Why don't sunfish have a tail?
They lose the tail fin during development. A stiff rudder called the clavus, formed from modified fin rays, takes its place, while the tall dorsal and anal fins provide propulsion by sculling side to side.

### What do ocean sunfish / molas eat?
Ocean Sunfish / Molas eat 2,300 kg — Heaviest recorded — the heaviest bony fish. The ocean sunfish (Mola mola) is the heaviest bony fish alive at over two tonnes, has no true tail fin, feeds largely on gelatinous plankton, and grows to around 60 million times its larval weight.

### Where do ocean sunfish / molas live?
Ocean Sunfish / Molas live in Temperate and tropical oceans worldwide, Open ocean, often near the surface. The ocean sunfish (Mola mola) is the heaviest bony fish alive at over two tonnes, has no true tail fin, feeds largely on gelatinous plankton, and grows to around 60 million times its larval weight.

### Are ocean sunfish / molas dangerous?
Ocean Sunfish / Molas are not generally dangerous to people. The ocean sunfish (Mola mola) is the heaviest bony fish alive at over two tonnes, has no true tail fin, feeds largely on gelatinous plankton, and grows to around 60 million times its larval weight. Give wild individuals space and do not corner or handle them.

### How long do ocean sunfish / molas live?
A precise wild lifespan for ocean sunfish / molas is not firmly established in the sources cited on this guide. The ocean sunfish (Mola mola) is the heaviest bony fish alive at over two tonnes, has no true tail fin, feeds largely on gelatinous plankton, and grows to around 60 million times its larval weight. Where longevity figures appear in the literature they vary by region, sex and whether animals are wild or captive.

### How big is an ocean sunfish / mola?
An Ocean Sunfish / Mola is about ~2,300 kg. The ocean sunfish (Mola mola) is the heaviest bony fish alive at over two tonnes, has no true tail fin, feeds largely on gelatinous plankton, and grows to around 60 million times its larval weight. Conservation status: Bycatch in drift and gill nets.

## Sources
- [IUCN Red List — Mola mola](https://www.iucnredlist.org/species/190422/97667070)
- [Smithsonian Ocean — Fish](https://ocean.si.edu/ocean-life/fish)

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Full guide: https://worldanimalrescuenetwork.org/wildlife-guides/ocean-sunfish