Like all of the mutant sub-species on Fasia, the Aquasi were subject to rapid evolution after settling on the planet, due to Fasia's unique properties. Those who settled near the coastline on the equitorial region evolved into the Aquasi after a few generations, growing gills, and various other adaptations, such as webbed feet and fingers which allowed them to swim more efficently. However, this does not seem to to have affected their ability to breath oxygen outside of water, allowing them to have landside settlements in addition to their underwater settlements.
The Aquasi were often attacked by the other Fasian species that set up coastline cities, in particular by the Sürunen, who wanted to stop them from 'stealing' the fish from their territory. This resulted in many Aquasi cities being built in the depths of the ocean, though over the centuries, many were build closer to the coastline. There are also some which braved the possibility of being attacked, and set up settlements in lakes within the Fasian mainland.
Perhaps due to their ability to breathe in both air and water, the Aquasi are defined in no small part by their natural curiosity of the universe around them. They appear to have a desire to explore the universe around them, which is why they were quick to come around to the idea of joining The Commune Federation when it arrived on Fasia.
The Aquasi have since been invaluable in settling various water worlds, and the exploration of those worlds. This unique role in the Federation has lead them to develop close ties to the Casorians in particular.