The ocean covers 71% of Earth's surface, yet more than 80% of it remains unmapped and unexplored. Traditional underwater vehicles — propeller-driven ROVs and AUVs — are effective but noisy, energy-intensive, and disruptive to marine ecosystems. Bio-inspired underwater robots offer an alternative: machines that move like fish, jellyfish, and rays, blending into the aquatic environment while consuming a fraction of the energy.
Fish Robots and Undulatory Locomotion
Fish swim by propagating a wave of bending along their body, generating thrust through interaction between their flexible body and the surrounding water. This undulatory locomotion is remarkably efficient — tuna can swim thousands of kilometers with minimal energy expenditure by exploiting the mechanics of their crescent-shaped tail and stiff body.
MIT's robotic tuna, first developed in the 1990s and continuously refined, demonstrated that a multi-segment mechanical fish could achieve propulsive efficiency approaching that of biological fish. More recent designs from laboratories in China, Japan, and Germany have produced fish robots capable of autonomous navigation, obstacle avoidance, and coordinated schooling behavior. The SoFi robot from MIT's CSAIL can swim alongside real fish at depths of 18 meters, capturing close-up footage without disturbing the animals.
Jellyfish and Manta Ray Designs
Jellyfish-inspired robots exploit a different propulsion mechanism: jet propulsion through body contraction. Researchers at Virginia Tech have developed Cyro, a large jellyfish robot powered by shape-memory alloy actuators, and Robojelly, which uses hydrogen and oxygen reactions on its surface to power continuous swimming without batteries — a concept that could enable indefinite ocean monitoring.
Manta ray-inspired robots, such as the Aqua-Ray from Festo and the MantaDroid from the National University of Singapore, use flapping pectoral fins for propulsion. This design offers excellent maneuverability and low-speed efficiency, making it ideal for coral reef monitoring and port inspection where precise station-keeping matters more than speed.
Practical Applications
Bio-inspired underwater robots are finding applications where conventional AUVs are impractical or undesirable. Environmental monitoring benefits from robots that don't produce noise pollution or turbulence that disrupts marine life. Pipeline and infrastructure inspection requires robots that can navigate confined spaces and maintain position in currents. Military applications include covert surveillance and mine countermeasures, where stealth is paramount.
Aquaculture — fish farming — is an emerging market. Robotic fish can monitor water quality, inspect net integrity, and herd live fish without causing the stress that diver interventions produce. Norwegian and Scottish salmon farms have begun testing robotic inspection platforms that reduce the need for human divers in cold, dangerous waters.
Technical Challenges
Underwater robotics faces unique engineering challenges. Radio waves do not penetrate seawater, so communication relies on acoustic modems with limited bandwidth and significant latency. Navigation is equally constrained: GPS does not work underwater, forcing reliance on inertial navigation, acoustic positioning, and dead reckoning. Pressure at depth requires robust sealing and materials rated for hundreds of atmospheres.
For bio-inspired designs specifically, the challenge is achieving the right balance between biomimetic fidelity and engineering practicality. A robot that perfectly mimics a fish may not carry enough payload or battery capacity to perform useful work. The most successful designs extract key hydrodynamic principles from biology while using conventional engineering wherever biomimicry does not add value.
