Researchers have reported new cases of “upside down” swimming in deep-sea ray-finned fish of the genus Gigantactis.

Scientists believe that these fish, known for their fearsome appearance and long, bioluminescent bait dangling in front of their mouths, probably spend their entire lives in an “upside down” position.

Researchers observed this unusual behavior while examining deep-sea images taken by various remotely operated underwater vehicles in the Atlantic, Pacific and Indian oceans. Long-stemmed sticks live at depths of 1,000 to 2,500 m and have not been adequately studied.

In 1999, a remote-controlled vehicle captured the first photograph of a stickleback swimming upside down between Hawaii and California. However, until recently it was believed to be a single incident. Years later, researchers observed similar behavior in different places and in different fish.

Scientists noted that such behavior is not limited to certain types of activities, but rather is “standard.” Scientists believe that the inverted position probably relates to a fishing rod-like appendage.

It is probably more convenient for the fish to manipulate a long bait in a belly-up position. In this position, it hangs from its upper lip to the bottom of the sea. This helps the fish find prey hidden among the bottom plants. Source