Out of the blue: Beautiful shoal of sardines captured by Nadya Kulagina
These breathtaking images show a vast school of sardines in the Philippines. The magnificent spectacle, known as a 'sardine run' sees the silver fish swimming in formation to create a shimmering wall in their annual migration.
The shoal was spotted off the coast of Pescador Island. It occurs in the region from May through to July when billions of sardines spawn in the cool waters of southern Africa and move north along the east coast and into the Indian Ocean.
Photographer Nadya Kulagina said: "We were exploring the abundance of marine life - frog fish, moray eels, octopi, sea snakes when suddenly the sky grew dark as if overcast with unexpected clouds. "I looked up and there were thousands, no millions of sardines moving as one organism. Their moving mass was blocking the sun turning day into night."