Aquan
The Aquans were the water-breathing natives of the planet . Living deep in Argo's oceans, they were an highly developed race, capable of fantastic architecture and medical triumphs unheard of in the galaxy. They were also capable of eradicating memories.

The Aquans had flat noses, long hair-like features on their heads, webbed hands, and loose fins on their ankles.

History 
According to Aquan legend, corroborated by Starfleet observations, Argo was once a land planet, and the Aquans were air-breathers. However, seismic disturbances started to sink the land.

Many air-breathers were mutated through Surgo-op. Although this was not evolution, the mutations became hereditary as the centuries passed. Despite being a highly developed race, the Aquans were theorized to have become savage and violent due to the frightening nature of these events. They hunted and killed air breathers. The water breathing Aquans feared contamination with this violence. Water breathers remained fearful of them long after they passed into legend.

Government and culture 
The Aquans were governed by a Ruling Tribunal of the Aquans, which was made up of a High Tribune and Junior Tribunes. They were guided by the Aquan ordainments.

By the mid-23rd century, Aquan history consisted of legends about violent air breathers. In fact, with their ancient records stating that air breathers never came in peace, they were always on the lookout for air breather spies.

Aquans were adverse to killing, even when it came to their hated enemies, air breathers. However this aversion was not absolute. The Aquan's main weapons were nets. Their edibles were gathered.

Ancient Aquans were demonstrated to have a written language, which was recorded on scrolls which could last for long periods under water. ()

Encounter with the Federation 
In 2269, the crew of the  visited Argo and discovered the underwater society, which at this time was experiencing ideological divisions between generations, and relations between the younger and older members of Aquan society were strained. 

Upon making contact with the Aquans following an accident, the Enterprise crew managed to re-aquaint Aquans with the context of their history, as well as redirect a major seaquake to an unpopulated area and in the process raise one of the sunken cities. This encounter with benevolent air breathers had an impact on Aquan culture. The younger Aquans planned to rebuild the above-water shelters, while the older ones felt they could not adjust to the thought of becoming air-breathers and planned to remain in their Aqua-City. The two factions planned to remain in contact. ()

Individuals 
Named
 Cadmar
 Cheeron
 Domar
 Lemus
 Nephro
 Rila

Unnamed
 Unnamed Aquans
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Species