German underwater photographers Kirsten and Joachim Jakobsen were about to finish their excursion in a small submarine off the coast of the Portuguese island of Sao Jorge in the Atlantic Ocean when they encountered an unusual sight.
In the dark sea at a depth of 800 meters, they saw light from a deep-sea catfish and for the next 25 minutes they followed it through a video camera. Biologists have since confirmed that it was the species Caulophryne jordani.
He and she together
Until now, knowledge of these fish has been limited to dead fish that have been caught in fishing gear, and the capture therefore causes great joy, not least because it was not just one fish but two, a spawner and a hook.
It is difficult to find a mate at this great depth, and when it finally happens, the hook bites into the spawn and releases various enzymes, which partially dissolve the skin on both fish.
The skin then heals again, and then the spawn and the hook have healed together and almost become one organism. For the rest of its life, the hen acts as a sperm bank for the spawn and in return receives from it the nutrition it needs.
The sperm bank with its own will
Biologists have never before been able to observe this peculiar symbiosis while the fish are still alive, and they were quite surprised that, despite the symbiont, the hookworm continues to have mobility that is independent of spawning movements.
The spawn on the recording is about 16 cm long, but the largest ones can reach a length of 20 cm. The pendant is much smaller, only 1.6 cm long.
