Renton surrounded by Skyfish in Episode 2.
Skyfish are creatures of the Scub Coral that have adapted to float upon trapar waves that fill the atmosphere. They have been shown to vary greatly in size. They are harvested to create a substance that is known as reflection film, which is what permits ships and LFOs to fly without the use of fuel-based propulsion using trapar. It is said that skyfish gather where positive emotions are emitted by humans in the presence of a Compac Drive. In one of the study guides Eureka gave to the kids, there is a page depicting what looks like different species of Skyfish.
Outside Eureka Seven[]
In reality, skyfish also refer to rods, a subject of cryptozoology.