what is the biggest fish in the world?

The whale shark. Whales are mammals, so they don't count. Whale sharks are fish, and they are the largest fish known to exist.

Damn many ppl here dont even know Whale isnt a fish, its a mammal.

Whale Shark is the biggest fish in da world. Whale shark is not a whale but a shark, it got the name bcoz it is biggest shark and is not a predator like other sharks.

The biggest fish is a Whale shark (this is actually a fish), a fully grown adult can weigh more than 12 tonnes. It's harmless and feeds mainly on plankton. It's mouth can measure 1 metre across but has extremely small teeth.

the whale shark is the biggest fish in the world. A blue whale is a mammal u thick idiots

The Whale Shark followed by the Basking Shark

The Whale Shark closely followed by the Basquing Shark

Is it the blue whale? Thats classed as a mammal though, but it lives in the ocean and looks like a bloody fish to me!

How about its name sake, the whale shark. Thats a hell of a big fish.

NO.. NOT the WHALE.., a whale is a mammal, the question was fish..,

I believe it may be either the Great White.., or the Beluga Whale.., Which in not a mammal.., but a fish.

I concede on this question..,the whale shark was the correct answer.., I just happen to of forgot it until I "saw" the correct one posted.

in the sea its the whale shark. in fresh water its a toss up between the sturgeon and a species of cat fish called the meekong catfish, one was caught 10 feet in length.

For saltwater, it is whale shark. It is not a whale, but almost the size of the whale. It is so call a shark but it eats planktons.

For freshwater, it is a giant catfish call meikong giant catfish in south asia, vietnam, thailand.