The water-breathing species of the planet Ockora were preyed upon by other air-breathing mammals from other planets of in the system. On some of those planets, culling Ockorans became an international sport, particularly among the Kalarians. After centuries of such treatment, the Ockoras created exoskeletal battle armour and even undergoing painful surgery. The Ockorans that wore the armour became known as the Selachians. They became one of the few water-based species to advanced beyond Level 2 technology, going as far as to develop space travel.
During a major culling festival, the Selachians attacked their predators from the depths. In response to the incident, Ockora was cordoned off by the other planets and as time went by, the Selachians began to fade from memory. However, the Selachians themselves did not forget, and eventually, without warning, they launched a war fleet against the planets immediately neighbouring Ockora. What followed was a series of long and brutal wars, from which the Selachians emerged victorious, taking control of the outlying planets such as Kalaya and Molinar. (PROSE: The Murder Game, The Final Sanction)
Even with their home system conquered, the Selachians continued to feel like victims and were paranoid that they were still in many ways inferior to air-breathers. Although they considered themselves a civilised race, who produced poetry and artwork, they developed an overriding urge to ensure that they never again experienced the abuse, terrors and resentment of the past by becoming aggressive. Seeking the resources required to build up their technology to remove their perceived inferiority to air-breathers, the Selachians expanded their influence beyond their home system. They made arms deals with companies on Earth, and killed many people as they ransacked other worlds for their resources. They were ultimately set on becoming the most powerful and feared race in the cosmos if it meant preventing repeats of the past. (PROSE: The Murder Game, The Final Sanction)
The Selachians continued to expand their power on the galactic market. Earth, still nervous of external threats after the 22nd century Dalek invasion, saw this as a threat to their own influence. Earth governments gave a powerful cartel of conglomerates permission to rebuild and fund the Terran Security Forces, which grew into an army capable of fighting an interplanetary war within five years. At the beginning of the 23rd century, the TSF went to war against the Selachian Empire and liberated all of the planets they conquered. Two planets in the Empire, Kalaya and Molinar, were lost in 2204. The Selachian retreat from Kalaya signalled the loss of the Empire's last conquered planet. Only the Selachian homeworld of Ockora remained, until it was destroyed by G-bombs. (PROSE: The Final Sanction)