Bryan McAllister’s personal reference notebook
July 30, 2026Short & citedBlog
Civic Viewpoint.
A quiet encyclopedia with a personal desk
Kept by Bryan McAllister — short guides, clear facts, and the Canadian angle when it matters.
Field Notes • Fish

Sunfish

Sunfish are a group of fish best known for the ocean sunfish, or mola, which is the heaviest bony fish.

Updated July 30, 20261 min readCited sources

Sunfish commonly refers to the ocean sunfish, the heaviest bony fish, but also includes freshwater sunfishes in North America. This page covers the ocean sunfish as the best-known type.

What it is

The ocean sunfish (Mola mola) is a ray-finned fish known for its unusual flattened shape and massive size, reaching up to 4 metres long and 2.5 tonnes. Freshwater sunfishes belong to the family Centrarchidae and are much smaller, often under 30 centimetres.

Key details

Ocean sunfish feed mainly on jellyfish and other gelatinous prey, but also eat small fish, squid, and crustaceans. They live in tropical and temperate oceans worldwide. Freshwater sunfishes inhabit lakes, rivers, and ponds across Canada and the United States.

Why it matters

Sunfish are generally harmless to humans and not aggressive toward swimmers. However, ocean sunfish are vulnerable to bycatch in fishing gear and collisions with boats, making them a concern for marine conservation.

In short

  • Ocean sunfish are the heaviest bony fish, reaching up to 2.5 tonnes.
  • They feed mainly on jellyfish and other gelatinous prey.
  • Freshwater sunfishes are widespread in Canadian lakes and rivers.
  • Sunfish are not dangerous to humans.
Canadian angle

Freshwater sunfishes are common in Canada’s lakes, rivers, and ponds, and the ocean sunfish is occasionally relevant to Canadian waters through Atlantic and Pacific marine ecosystems.

Quick questions

What is a sunfish?
A sunfish is either an ocean fish from the family Molidae or a freshwater fish from the family Centrarchidae. The best-known sunfish is the ocean sunfish, Mola mola, a very large, flattened marine fish.
How big do sunfish get?
Ocean sunfish can grow to about 4 metres long and weigh up to about 2.5 tonnes. Freshwater sunfishes are much smaller, often under 30 centimetres depending on species.
Are sunfish dangerous?
No, sunfish are generally not dangerous to humans. Large ocean sunfish can be injured by human activity, and people should avoid handling them closely, but they are not aggressive toward swimmers.

Sources

  1. U.S. National Park Service — https://www.nps.gov/amis/learn/nature/sunfish.htm
    Supports: Freshwater sunfishes are widespread across the continental United States and Canada; they occur in rivers, lakes, and ponds.
  2. National Geographic Kids — https://kids.nationalgeographic.com/animals/fish/facts/mola
    Supports: Ocean sunfish size, global tropical and temperate ocean range, and harmlessness to humans.
  3. Smithsonian Ocean — https://www.smithsonianmag.com/science-nature/mola-mola-oceans-gentle-giant-180952971/
    Supports: Ocean sunfish diet, open-ocean habitat, and lack of danger to humans.
  4. Animal Diversity Web — https://www.animaldiversity.org/accounts/Mola_mola/
    Supports: Ocean sunfish distribution in tropical and temperate oceans and diet including jellyfish and gelatinous zooplankton.
  5. Hebridean Whale & Dolphin Trust — https://www.hwdt.org/sunfish
    Supports: Ocean sunfish range, diet, and notes on bycatch and boat collisions.