A robotic fish uses electronic blood to power itself. The design is very energy efficient and the creators say it can swim non-stop for 36 hours
Source:
https://www.newscientist.com/article/2207175-robotic-fish-powered-by-electronic-blood-can-swim-for-36-hours/?utm_campaign=RSS%7CNSNS&utm_source=NSNS&utm_medium=RSS&utm_content=home