The world's first autonomous robotic fish are the latest attraction at the London Aquarium.
The fish move in a very realistic way
Biologically inspired by the common carp, the new designs can avoid objects and swim around a specially designed tank entirely of their own accord.
This new kind of cyber-fish took three years to develop, by a team of scientists from Essex University.
Future generations may be used for seabed explorations, detection of leaks in oil pipelines, or even as spies.
Although robotic fish have been investigated for the last 10 years or so, the creators of the new models claim theirs are the smartest yet.
"We have embedded sensors on board - so, unlike the previous fishes that have remote controls, these are fully autonomous and artificial-intelligence based," lead researcher Professor Huosheng Hu, told the BBC News website.
Their undulating movements are also said to be more realistic.
"This one is more life-like - it mimics normal swimming and sharp turning," he explained. "People get confused and think it's a real fish."
The fish are about 50cm long, 15cm high and 12cm wide (20in by 6in by 5in), and covered with bright scales that reflect light.
The maximum swim speed is about 50cm (20in) per second but the fish have been slowed down to less than half that, to help prolong battery life - up to five hours.
In the future, the Essex team would like to increase the robots' intelligence - so that an individual machine could recharge itself as required.
"We want the fish to have the ability to look for its own charging station, just like a real fish looking for food," said Professor Hu.
It is hoped that bringing the public into direct contact with robots will increase their understanding of science and technology.
"It should be entertaining and fun for the visitors. Our main thing is obviously live fish, but the robotic side is really fascinating," said Michael Michaels, general manager of the London Aquarium.
The three robots will live alongside real fish in a tank in the aquarium, and will be named by children in a competition.