Minami Hatanpo is one of the most abundant small nocturnal fish in the coral reef area, and is about 15 cm in length.During the day, in the darkness of underwater caves in coral reef areas, groups of dozens to thousands of individuals are formed.However, at night, it disappeared from the hideout in the daytime, and its destination and actions were completely unknown.

　Nocturnal fish are sensitive to light and cannot be observed with light.Therefore, this time, we attached a small glowing tag to the collected fish and released it.Observers followed it by swimming in the sea at night.In addition to careful investigation and preparation, the pursuit was carried out in the jet-black night sea with sufficient support.

　As a result, Minami Hatanpo went offshore outside the coral reefs at night and migrated extremely long distances.After sunset, they started migrating from the underwater cave all at once, reaching 1m in the longest case and about 700m in the shortest one after about 400 hour of observation.It was estimated that the fish would continue to move, moving up to 7 km overnight.

　The inside of the coral reef is oligotrophic, but the zooplankton hidden in the seabed during the day rises into the water at night and becomes nutritious, and the movement to the outside is advantageous for spawning and feeding.In fact, this fish grows fast and breeds frequently, making it an important food resource for predators.At night, it returned to the coral reef to excrete feces, and it was found that it plays an important role in the energy circulation of the ecosystem inside and outside the coral reef.

　The research group hopes that this new method will be utilized in future research on nocturnal fish and will lead to an accurate understanding of fish ecology.

Paper information:[Peer J] Night time migrations and behavioral patterns of Pempheris schwenkii