Hath

The Hath were a race of piscine humanoids. (DW: The Doctor's Daughter)

Appearance
Hath were a humanoid race with purple and orange fish-like skin and a small headcrest running along the top of their heads. They were slightly taller than most Near-Humans. (DW: The Doctor's Daughter)

Technology
The Hath shared a lot of technology with the Humans they were allied with, such as guns and generation chambers. The only technology that was only used by the Hath, however, was a structure attached to each Hath's mouth. This structure was metallic with a glass casing for a bubbling green liquid. It purpose was not explained in the episode, but actions suggest it adds the Hath in breathing and communication. (DW: The Doctor's Daughter)

History
The Hath were a race which allied themselves with Humans, and took part in the colonisation of Messaline in the July 6012 of the New Byzantine Calendar. However, with the death of the mission commander, there was a power vacuum and both species fought to take the planet for their own.

After a seven-day battle, the two races found the "Source", an artefact that mythologisation had led them to believe was the breath of the creator. Due to the efforts of the Doctor, Jenny, Donna Noble and Martha Jones (the latter who had allied herself with the Hath) the Source was broken and terraforming gases within escaped, and the two races were to peace. (DW: The Doctor's Daughter)

Behind the Scenes
It was rumoured Hath were red bubbles that communicate through expanding and letting out smaller bubbles. It was also rumoured one of them would kill Jenny at the end of the episode. While bubbles did appear to be the Hath's only form of communication, Doctor Who Confidential showed that lines were actually scripted for the Hath (even if they only groaned throughout the episode).