Ocean STEMulation: Robotic Fish Get Lateral Line Sensing

Focusing on science, technology, engineering, and math (STEM), as they pertain to the ocean.

How do fish sense water flow?
Many fish have the ability to sense patterns of water flow around them using the lateral line system. This is a network of sensory organs that can detect water flow. Hair-like cells called neuromasts, which are located either in pores on the skin or directly on the surface, respond to vibration and movement in the water. This lets the fish determine the velocity and acceleration of the flow

This ability is called lateral line sensing because, usually, the network of sensors runs in a line pattern along the length of the fish’s body. That line is often nearly invisible, but in some cases it can be seen as a narrow stripe. They also can have additional pores around the head. Some amphibians have lateral line sensing abilities as well.

Different organisms create different wake patterns when they move, so being able to detect that movement in the surrounding water is very useful and helps to identify prey and predators. It also helps the fish move in a more energy efficient way by locating places where the currents will be helpful for swimming, and it helps schools of fish move together without bumping into each other.

In some species of fish, such as the rainbow trout, top, the lateral line is visible as a stripe. In other species, such as the common roach, bottom, detecting the grooved scales of the lateral line it requires a much closer look.    
Photos via Wikimedia Commons by: U.S. Forest Service, Sawtooth National Recreation Area, Fredlyfish4, Public Domain (top).
Piet Spaans, Viridiflavus, Creative Commons (bottom). 

Technology mimics nature.
So far, underwater robots have been able to navigate using just cameras and sonar, but scientists have now found a way to equip them with flow-sensing capabilities similar to the lateral line sensors of fish.

Scientists with the FILOSE project first built a robotic fish. Its structure and movement were created to be similar to that of a rainbow trout. A motor powers the tail, which propels the model fish forward while the head stays mostly still.

They then created an artificial lateral line using microscopic filaments that bend along with water flow. The tiny cantilevers imitate the neuromasts of a real fish. They can be placed on chips, which are then attached to the robotic fish.

The robotic fish and its artificial lateral line together make up the first flow-sensing underwater robot, which the scientists tested out in a flow tank.

The robot can detect the direction and velocity of water flow, and change its swimming speed to move upstream or hold its position. It can also find places of low flow to hover – for example, by lurking behind another object to save energy. Essentially they are detecting and responding to the “flowscape,” (flow landscape) something other underwater robots right now cannot do. This has many applications, including helping underwater robots run more efficiently, mitigating the common problem of limited battery life, and helping them adapt to changes in water conditions. Before this research, the lateral line found in nature had no technological equivalent.

All of this work is part of a field of research called biomimetics or biomimicry, in which scientists create things that are inspired by nature. By imitating nature, they hope to find answers to human problems. We’ve written about such work before: click here to learn about how studying squid skin could lead to smart clothing for people. There are also other studies featuring robotic fish - click here to read about how one known as robofish was used to study schooling behavior. 

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