This huge sunfish was spotted off the coast of Mumbles, Swansea

A family were stunned when they spotted the world's largest bony fish off the coast of Mumbles during a fishing trip.

Sililo Martens recorded the encounter on his mobile phone and the occupants of the boat can be heard discussing whether it's a shark or a dolphin before someone says "no it's not look how big that is, that's a huge fish!".

Although it took them a while to work out what they were looking at, it turned out to be an Ocean Sunfish (or Mola Mola).

These giants of the sea can weigh as much as a car and are usually found in tropical waters.

Last week, one of the huge sea creatures which can grow up to 10ft long, was seen off the coast of Dorset.

The fish's name refers to its habit of basking in the sun close to the water's surface, which might explain what brought it to Welsh waters on one of the hottest days of the year on Wednesday, June 24.

Sililo was on his speed boat near to Mumbles Pier when he saw something in the water as he was on his way back from a fishing trip with his two sons and his friend, Ollie, and his son.

They thought they had spotted a shark (Sililo Martens)

But when the creature turned on its side it was clear that it was something else (Sililo Martens)

He stopped one of his sons from jumping into the water because he thought the creature was a shark at first. 

There was no need to worry though - Sunfish are harmless to humans but can be very curious and often approach divers.

The unusual-looking fish is often as tall as it is long, and when it swims near the surface its dorsal fin can see them mistaken for sharks.

"My son was just about to jump in the water when I spotted the black fin from about 20 metres away.

"Straight away it looked like a shark fin and when we got closer it looked more like a Dolphin and then, only until we got right up next to it, we could see it was this beautiful enormous fish," he said.

Sililo lives in Swansea but used to live in Tonga, a tropical island in the Pacific Ocean.

"In the 20 years I've been in the UK it's the first time I've seen anything like this over this way," he added.

The boat the fish was spotted from is 18ft long and Sililo said that the Sunfish was "at least a third" of the length of the vessel.