Japan's Fisheries Agency says its fishery research vessel has succeeded in filming bluefin tuna spawning in a natural environment. The agency says it is rare for bluefin tuna spawning in nature to be recorded. Officials hope the visual record will contribute to studies that will shed light on their ecology and protect stocks.

The video was filmed by the Kaiyo-Maru, which was conducting a survey on stocks of bluefin tuna in waters around the Nansei Islands in southwestern Japan.

Agency officials say crewmembers of the vessel found a group of large fish exhibiting spawning behavior shortly after 6 p.m. on June 4 and recorded the activity.

The officials also say multiple experts checked the footage and determined that the fish were bluefin tuna based on such factors as body color and the shape of the fins.

The video was taken from the vessel. It shows a female bluefin tuna swimming in an arc near the surface of the sea, with several males chasing her in a line.

The officials say fertilized eggs about one millimeter in diameter were collected from nearby waters. They say they plan to conduct a genetic analysis.

It is said bluefin tuna usually spawn after sunset, but officials say the video was filmed while it was still light.