A 57-year-old man was attacked and killed by the crocodile in front of his wife while they were fishing at the Adelaide River, about 60km east of Darwin, on Monday afternoon.

The man was taken when he got into the water to unsnag his fishing line.

Police and rangers scouring the crocodile-infested river by boat on Monday night shot and killed a 4.5m crocodile and the man's body was recovered later that night.

His wife was treated by paramedics at the scene for shock.

The Adelaide River is well known for its Jumping Croc tours, where boats travel the river and crocodiles jump for meat attached to hooks.

"Michael Jackson was one in a million, and unfortunately being an albino would have been picked on by all the others, its a big pecking order," said Rob Marchand, owner of Wallaroo Tours, which runs Jumping Croc cruises across the river from where the man was taken.

He told the ABC on Tuesday that the crocodile had been in that part of the river for several years, and that the crocodiles had been fighting a lot recently, jockeying for position and preparing to breed.

He said only the strongest and most aggressive crocodiles reached four metres or longer.

"The croc has only been doing what nature intends it to do, and that's survive," Mr Marchand said.

"They know how to do three major things: eat, reproduce and aggression ... if you're not going to look after yourself, you'll find yourself being eaten."

Crocodiles shouldn't be blamed for their natural behaviour, he said, and rejected the suggestion that the Jumping Croc tours were encouraging predatory behaviour on the Adelaide River.

"I'm sure crocs knew how to eat people a long time before we come along," he said.

The attack is the third this year, after a boy was taken at a billabong at Jabiru in January, and another fisherman was snatched off his boat as he emptied a bucket in a Kakadu River two months ago.

A crocodile was also shot on the Tiwi Islands two weeks ago, suspected to have killed a local man who disappeared and has yet to be found.

But tests on the organic matter found in its stomach haven't yet produced a conclusive result.