Horatio the goldfish has being amusing its owner and guests for five years now with his unusual habit of swimming around with his belly upwards.

The fish first displayed its crazy behaviour one year after Richard Gordon, from Gosport in England, was presented the pet by his grandson.

The 63-year-old said he thought at first the fish was dead and was going to flush him away. But Horatio turned out to be quite alive and happy with his directional preferences.

“Strangely, when I put food in he'll always swim up to it the right way round,” Gordon said to the Telegraph newspaper.

Fish experts believe Horatio may have problems with his swim bladder – an air-filled organ that allows fish change its buoyancy and thus move up and down. If the bladder gets deflated or misshapen, the fish will have trouble keeping its position much like a human with an inner ear dysfunction.

But Gordon disagreed, saying: “He seems to be able to easily rise to the top and swim to the bottom.”

The goldfish got his name after Lord Nelson because Richard Gordon married his wife Diane, 62, on Trafalgar Day.