Dolphins are dumber than goldfish.

In fact, the brains of the adorable mammals of the deep are so poorly organised, they don't have the intelligence to jump out of enclosures - unlike goldfish.

Research by Wits University Professor Paul Manger shows that the dolphin is dumb. Its brain may be large, but only so that it can generate heat to keep warm.

Manger, a neuro-ethologist at the university's school of anatomical sciences, published his controversial seven-year research in the Cambridge Philosophical Society journal in March. He will present his findings at Wits' Health Sciences Research Day on Wednesday.

On Wednesday, Manger said the misunderstanding about the dolphin's intelligence was because people equated the size of its brain with high intelligence.

He said it had been proved that a dolphin's brain was a poor processor of information.

"The problem is people assumed all brains are organised the same way, and they are not. The dolphin's brain is poorly organised."

Manger said that in aquariums, dolphins were usually kept in uncovered pools because they were not smart enough to think of jumping into a neighbouring enclosure.

"The dividers between their pools are only about 20cm above the water. But they don't try to get out and escape - a goldfish will do it."

"Even rats, if you put them in a shoe box, will try and climb over the wall."

Manager said it took up to five years to train a dolphin, and that was done through a stimulus response system - where the mammal was rewarded for what it did.

"Compare a dolphin to a sheep dog: the dog can be trained to control a flock of 30 sheep. But dolphins don't have that level of intelligence," Manger said.