Scientists will put some robot fish into the sea near Spain. These robot fish will help people find out the pollution in the water. If the robot fish are able to finish their work successfully, the scientists hope that the fish will be used in rivers, lakes and the. sea around the world. The robot fish are about 1.5 meters long. There will be a detector in their bodies. It can find the pollution in the water, and then the robot fish will eat part of it. Unlike other robots, they don' t need to be operated (操作) by people far away. The robots al} have an eight-hour battery (电池). They can "swim" in the sea freely and send back information to people on the beach. After their batteries run down, they will go back to the beach by themselves. There are five robot fish altogether, Each costs (花费) about 29,000 dollars. They are part of a three-year project (项目) between engineering company BMT Group and the University of Essex in England.