Watching footage from 6,000 meters below the ocean’s surface can be almost disorienting. A human body would be crushed in a matter of seconds by the cold, lightless water. On screen, however, a fish appears to move effortlessly past the camera. The image, which was taken by remotely operated vehicles diving off the coast of Puerto Rico, is the focal point of a recent study that is changing the way marine scientists understand where and why fish can live.
The study, which was published in the ICES Journal of Marine Science in 2026, gathered 1,137 observations of deep-sea fish in the tropical Atlantic and Caribbean Sea over a depth range of six kilometers. Video from thirty different exploration dives was examined by scientists from SUNY Geneseo, NOAA Ocean Exploration, Woods Hole Oceanographic Institution, the Smithsonian, and several other organizations. NOAA’s ROV Deep Discoverer, ROV Global Explorer, and the well-known submersible Alvin were among the vehicles utilized. Some long-held suspicions were confirmed by what they documented, while others were complicated.
On the surface, the pattern was fairly obvious: the deeper you go, the fewer fish you find. Both abundance and biodiversity gradually decreased with depth. It was not surprising. The specifics surrounding that overarching pattern were what made the study truly fascinating. Cusk eels, which belong to the family Ophidiidae and have been understudied for years, dominated observations at abyssal and hadal depths, close to and inside the Puerto Rico Trench itself. The fact that they are so common at such low depths begs serious questions about why this specific family is so adapted to environments that exclude almost everything else.
Researchers keep coming back to the question of body shape. In contrast to the more rounded species found higher up, fish seen at deeper depths tended to be elongated and eel-like. According to the working theory, this shape facilitates effective movement and may aid in vibration detection, which is a helpful ability when there is virtually no light. It is conceivable. Additionally, it makes some intuitive sense when you consider animals that have developed over millions of years to survive in an environment that is completely intolerable to most other creatures.
Fish that are typically thought of as pelagic—that is, swimming through open water rather than close to the ocean floor—are one of the study’s more bizarre findings. On camera, some of these species were seen doing the exact opposite: hovering close to the seafloor, interacting with the bottom, and, in a few instances, barely escaping predatory anemones that were hiding there. This type of behavioral observation is just not possible with a trawl net. To see something like that, you need real-time footage taken in the real world.
The video also showed trash, which is more difficult to discuss as a scientific discovery. Throughout the dive recordings, human debris was seen frequently, even at considerable depth. The fact that it is visible in the video serves as a reminder that the deep sea is not as remote from human activity as it once appeared, even though it was not the study’s main focus. Even in the middle of a paper about fish ecology, that detail has a sobering quality.
It’s also important to note who performed the majority of the analytical work in this case. Because the study was designed as a course-based undergraduate research experience, SUNY Geneseo students acted as researchers, formulating hypotheses, organizing data, and summarizing findings. It’s not a footnote. Students who encountered these species for the first time in their careers contributed to the expanded depth ranges and regional records reported in this paper. It will be interesting to see if that research model spreads. It appears to be effective.
