Hitchhiking to the abyss

We investigated, for the first time, the hitchhiker -host fidelity of deep-diving whale sharks and Chilean devil rays. We found that two of the most ubiquitous oceanic hitchhikers, the common remora and the pilot fish, are able to follow their hosts to bathypelagic depths, where they are exposed to extreme gradients of light, dissolved oxygen, temperature, and pressure. We documented a deep dive of a large whale shark hosting remoras and pilot fish. Common remora was observed at the deepest section of the dive, at 1460 m, where the water temperature was 3.6 degrees C. A pilot fish was recorded at 900 m, during the ascent phase, with the water temperature of 7.5 degrees C. Although the adaptations that allow these hitchhikers to mitigate the impacts of such extreme environmental conditions remain unknown, we discuss these findings in the framework of the ecophysiology of deep diving and the hitchhiker -host fidelity.

Automated summary

For the first time, we investigated the hitchhiker-host fidelity of deep-diving whale sharks and Chilean devil rays. We found that the common remora and pilot fish, two ubiquitous oceanic hitchhikers, can follow their hosts to bathypelagic depths with extreme environmental conditions. We documented a deep dive of a whale shark hosting remoras and pilot fish, with the common remora observed at the deepest section of the dive at 1460 m and the pilot fish recorded at 900 m during the ascent phase.