A Russian Soyuz rocket has launched from the Central Asian spaceport of Baikonur Cosmodrome in Kazakhstan on a mission to the International Space Station (ISS).
It is carrying a three-man US-Russian crew who are on a two-day trip to the orbiting laboratory. Thirty-two fish are also coming along for the ride.
The medaka fish are being taken to the space station as part of an experiment to study how fish adapt to the absence of gravity.
They will live inside a space-age fish tank, called the Aquatic Habitat, which was delivered on an earlier flight.
American astronaut Kevin Ford and Russian cosmonauts Oleg Novitsky and Evgeny Tarelkin and their fishy companions will join three other astronauts currently aboard the ISS.
At a prelaunch news conference, veteran NASA space shuttle pilot, Kevin Ford said: