What is the world’s largest fish by body mass?

The whale shark is the world’s largest fish by body mass.

Despite its name and enormous size, the whale shark is a fish, not a whale. It breathes with gills and belongs to the shark family. Confirmed individuals can reach around 18 metres, although many adults are smaller. Its broad mouth and patterned body make it one of the most recognizable ocean animals.

Whale sharks are filter feeders. They swim with their mouths open and strain plankton, small fishes, and other tiny organisms from seawater using specialized filtering structures near the gills. They may feed at the surface, where plankton concentrations can be high, and sometimes gather around seasonal food blooms.

The species is generally gentle and is not considered a threat to people. It occurs in tropical and warm-temperate oceans, often undertaking long migrations. Its exact lifespan and reproductive biology remain difficult to study because individuals range across vast areas.