A deep-sea fish known as Scalicus engyceros, dubbed the fish-prawn hybrid,
was filmed walking backward for the first time, revealing unprecedented locomotion in marine life. Researchers from Sun Yat-sen University observed the armored searobin using specialized fin rays to scuttle across the seafloor in the South China Sea, with footage confirming its ability to move sideways and backward—a behavior never before documented in fish.
The discovery, detailed in a study published in Ocean-Land-Atmosphere Research, marks a paradigm shift in understanding deep-sea fish adaptations. Using human-occupied and remotely operated submersibles, scientists captured the Scalicus engyceros, an armored searobin first described in 1872, demonstrating locomotion that mimics both crabs and shrimp. This study delivers a paradigm-shifting revelation: the deep-sea fish Scalicus engyceros is among the few fish species known to walk,
said Han Tian, the study’s primary author.
Unveiling the Walking Fish’s Unique Adaptations
The armored searobin’s anatomy defies conventional fish morphology. Its pectoral fins have evolved into flat, round plates that aid balance, while its shrimp-like fin rays and tail enable explosive, jerky leaps when threatened. The fish also possesses outward-extending barbels—whisker-like appendages that resemble a farmer’s rake. These barbels, though awkward for walking, provide an advantage in probing, digging, or hunting for food buried in the sediment,
according to the research team.
Footage from the human-occupied submersible Shenhaiyongshi (translated as deep-sea warrior
) revealed the fish moving backward, a motion described as “moonwalking” by researchers. This behavior, combined with its sideways scuttling, challenges previous assumptions about fish mobility. These walking fish harbor far more novel behavioral and evolutionary adaptations than previously assumed,
Tian added.
Deep-Sea Technology Enables New Insights
Modern deep-sea exploration vehicles have transformed how scientists study marine life. The research team used the Shenhaiyongshi and Haiqin submersibles to observe the searobin at depths of 1,148 to 1,640 feet, where light is scarce. By observing deep sea animals alive in their surrounding environment, we can gain insight into the adaptation and evolution of the species,
Tian explained. This in situ observation contrasts with earlier studies relying on preserved specimens, which limited understanding of the fish’s live behavior.
The study also noted the fish’s unusually large eyes. While the creature did not react to the submersible itself, it moved its eyes in response to the vehicle’s light beam. This suggests some sensitivity to light, raising questions about its habitat history. Modern deep-sea diving vehicles allow not only discovery of new species but also add a new in situ, functional dimension to the study of species based solely on the morphology of preserved specimens,
Tian said.
Implications for Marine Biology and Conservation
The findings underscore the importance of deep-sea exploration in uncovering hidden biological diversity. Scalicus engyceros, once thought to be a passive scavenger, now appears to have complex foraging and escape strategies. Its ability to “walk” and leap suggests adaptations to the South China Sea’s dynamic seafloor environment, where food sources may be buried or elusive.
Researchers emphasize that such discoveries highlight the need for continued investment in deep-sea technology. The deep sea remains mysterious today with so many unknowns,
said Tian. Modern deep-sea diving vehicles allow not only discovery of new species but also add a new in situ, functional dimension to the study of species based solely on the morphology of preserved specimens.
What’s Next for Deep-Sea Research?
While the study focuses on Scalicus engyceros, it opens avenues for investigating other armored searobins, such as Paraheminodus murrayi and Peristedion liorhynchus, which were also observed during the dives. Scientists plan to analyze more footage to determine if backward locomotion is common across the family or unique to this species.
The research also raises questions about the evolutionary pressures driving such adaptations. By observing deep sea animals alive in their surrounding environment, we can gain insight into the adaptation and evolution of the species,
Tian explained.