Robotic fish designed to protect real ones from pollution

A prototype robotic trout that can help farmers monitor ocean pollution levels has been developed by an engineer from Imperial College London.

Farmers normally locate their fish farms close to shore or they are cultivated in large salt-water tanks, ensuring easy access and delivery of fish to markets.  However, a major problem of fish farming in these environments is pollution.  Currently, pollution levels are monitored using unmanned, underwater robots or sensors.  However, they are notoriously unwieldy, often inefficient and noisy, which scares the fish.

Dr Jindong Liu and his colleagues have developed a fully autonomous prototype robotic trout.  The robo-fish, called Ichthus V5.5, is currently in South Korea, where it is undergoing field tests in the Han River.  The team says their robotic trout is 50 per cent more energy efficient, and has increased manoeuvrability compared to conventional underwater robots.  Bristling with sensors, the self-navigating robot mimics how real fish swim, monitoring for signs of environmental degradation.

Ultimately, the team envisages a school of robotic trout swimming around farm enclosures, working together to test for toxic chemicals and other harmful substances in multiple locations, as well as monitoring for changes in water temperature.

Dr Liu, from the Department of Computing at Imperial, says: “Food producers are under increasing pressure to provide larger quantities of high quality protein, in order to meet the demands and tastes of an increasing world population.  As seafood is rich in protein, fish farming is a great way to harvest marine produce sustainably.  We’ve developed a prototype robotic trout that mimics the swimming capabilities of real fish, seamlessly blending into their environment to monitor pollution levels.  We hope that they could be like the robotic guard dogs of the sea, on constant patrol, protecting the fish from pollution outbreaks.”

Inspired by nature

Measuring half a metre in length and weighing in at around 4.7kg, Ichthus has been specifically designed to mimic the movement of real fish, with its body split into three distinct sections.  By using detailed observations of carp swimming patterns, the team devised an algorithm that enables each body part to move in sync with each other to manoeuvre through the water.  It also uses GPS technology to navigate.

Unlike conventional underwater robots, which use propellers to drive them, Ichthus propels itself by oscillating its tail, just like a real fish.  The team replicated the smooth, undulating swimming motion used by fish such as tuna, carp and trout.  To do this they devised a mathematical function, enabling the tail to move independently of the body as in nature, and power the fish through the water. 

Increased efficiency and manoeuvrability

The reason for taking inspiration from the natural world is all down to maximising efficiency, says Dr Liu, who built the original robo-trout prototype while doing his PhD at the University of Essex.  Migrating animals, for example, must travel hundreds of miles around the globe, and it is essential they conserve as much energy as possible, adds the Imperial researcher.  Birds flying in formation or dolphins swimming between locations actually harness the energy of the environment that surrounds them.  “Each thrust of a dolphins tail creates a vortex behind it, allowing it to take energy from the water, and push it forwards, and we’ve mimicked this in our robotic trout”, explains Dr Liu. 

The oscillating tail and smoother swimming motion of Ichthus mean the fishy robot can swim up to 50 per cent more efficiently than traditional, propeller driven submersibles.  A gyro and an accelerometer on board work to keep the fish upright and moving, and when the battery is running low, Ichthus simply returns to a floating docking buoy to recharge.

As well as being more efficient than its predecessors, Ichthus’ turning radius is just one tenth of its body length, making it far more manoeuvrable in shallow waters.  Sensors that are located on the fish’s body detect to rising acidity levels, which could harm the fish. There also ultrasound and water pressure sensors that allow it to self-navigate around any obstacles in its path.

Securing the seas

Not only is the robotic fish a reliable guardian of its living counterparts, but it is hoped that submersible robots such as Ichthus will be used for other security jobs in the future, such as scanning the hulls of ships in port for damage and imperfections.  An inbuilt camera stores images to an internal memory card, while other essential data such as location, depth and temperature can be remotely beamed to the nearby docking buoy.  

Looking to the future for Ichthus, the team hopes to develop underwater communication between the fish, perhaps through mimicking the sonar system of dolphins, or even utilising the electrical impulses of eels. 

The device is currently undergoing tests at the Korea Institute of Industrial Technology. A study about the robo-trout was published in the January 2015 issue of the ‘Journal of Bionic Engineering’.