SCIENTISTS on the Indian Ocean island of Reunion have discovered hundreds of fish of unknown species, floating belly-up in the sea, following a spectacular volcanic eruption over the past week.

"It's crazy. We've never seen this with previous eruptions," said Alain Barrere, a scientific adviser to the island's Volcano Observatory.

Along with two scientists working for Reunion's aquarium, he collected specimens of the dead fish, which have bulging eyes, heads sometimes protracted by a beak and appear to have surfaced from depths of about 500 metres.

Mr Barrere said he hoped the specimens would help them determine "where they came from and how they died".