Arriving a few days ago aboard the HTV3 cargo rocket launched by JAXA (the Japanese space agency) on July 20th and docked on the 27th, the aquarium loaded with a group (hardly enough for a school) of Medaka fish (Oryzias latipes) which will be used to study the effects of weighlessness on vertebrate fauna.

Medaka are useful as they grow and spawn quickly and are also semi-transparent, making observation of their inner organs simple during their time aboard the ISS and later back on Earth.

In addition, the fish's genome has been fully sequenced, simplifying the identification of any genetic changes brought about by exposure not only to weightlessness, but to the higher radiation levels experienced on the ISS.

"We think studies on bone degradation mechanisms and muscle atrophy mechanisms are applicable to human health problems, especially for the ageing society," said Nobuyoshi Fujimoto, associate senior engineer at JAXA.

Being rapid breeders, it is hoped that three successive generations of Medaka will be laid as eggs, hatch and grow to reproduce themselves during the 90-day voyage before hitching a ride on a returning capsule.

The fish are housed in a special "Aquatic habitat" which has been designed for a variety of purposes, including the possibility of frogs on a subsequent trip.

We may-yet have "pigs in space" in just a few more years!