Two-headed sharks are becoming more common and no one knows why

A large reduction of the gene pool caused by overfishing is blamed for the deformity

A two-headed catfish shark embryo discovered in a Spanish laboratory

An increasing number of two-headed sharks are being reported in the wild, leaving scientists unable to explain why.

Over the last few years, a growing number of these genetic aberrations have been discovered and examined by scientists.

Professor Valentín Sans Coma, from the University of Malaga, studied the embryo of a two-headed catfish shark in a laboratory condition alongside 800 other shark embryos.

He has claimed a genetic disorder is the most reasonable explanation for the mutation as the unborn fish were not exposed to any infection, chemicals or radiation, reports the National Geographic.

Regarding wild sharks, scientists have blamed the mutation on a cocktail of factors including viral infections, metabolic disorders and pollution.

After studying a two headed smalleye smooth-hound shark and a two-headed blue shark, marine scientist Nicolas Ehemann claimed overfishing was probably to blame.

She explained overfishing had massively reduced the fish gene pool, making genetic disorders such as having two heads more common.

The issue facing scientists looking to study this phenomenon is that two-headed sharks generally do not live long.

Professor Ehemann said: "I would like to study these things, but it's not like you throw out a net and you catch two-headed sharks every so often. It's random."