Not plenty of fish in the sea!

Contrary to popular belief, there are not a lot of fish in the sea, say researchers.

A marine apocalypse may have been followed by a re-emergence of life in watery environments on land

Despite covering 70 per cent of the earth’s surface, marine environments contain only 20 per cent of all its species.

In the new study, scientists made the surprising discovery that freshwater rivers and lakes contain more fish species than salty oceans.

Yet freshwater environments occupy only two per cent of the earth’s surface.

It could be evidence of life reinventing itself after mass extinctions long ago, experts believe.

The findings suggest that most marine fish alive today are descended from fresh-water ancestors, even though life is thought to have first evolved in the oceans.

A marine apocalypse may have been followed by a re-emergence of life in watery environments on land.

The findings are published online in the journal Proceedings of the Royal Society B.

A team led by John Wiens, from Stony Brook University in New York, studied the biodiversity of ray-finned fish, which make up 96 per cent of all fish species.

The scientists created evolutionary trees based on molecular data and fossils, and a large database of fish habitats.

“There are more fish species in freshwater than in saltwater habitats, despite the much greater area and volume of the oceans,” said Dr Wiens.

“More remarkably, our re-sults suggest that most marine fish alive today are descended from fresh-water ancestors.

“Our results suggest that ancient extinctions in the marine environment may have wiped out the earliest ray-finned fishes living in the oceans, that the oceans were then re-colonised from freshwater habitats, and that most marine fish species living today are descended from that re-colonisation.

“This pattern of ancient extinction and more recent re-colonisation may help explain why the oceans are now so species-poor, even for fish.”