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. They breathed nutrient liquid rather then air and thus when in a Human-breathable atmosphere they used a breathing structure attached to their mouth. (DW: The Doctor's Daughter)

Technology
The Hath possessed Progenation machines and generation chambers just like the Humans they were once allied with. They used the machines for the same purpose as their enemies, to create new soldiers. The Hath carried heavy duty blaster rifles that fired a barrage of bullets usually accompanied by a long plume of flames emitted from the barrel of the gun. The Humans carried guns with the same overall effect but with a different design. The Hath wore special tubes full of nutrient liquid which they used to breathe and communicate. They also had the same holographic mapping system as the humans and when the Doctor uncovered the suppressed layer of information it showed up on the Hath map as well. (DW: The Doctor's Daughter)

History
In 2010 a Hath was seen at a bar when the Doctor came to visit Jack Harkness one last time before his regeneration. (DW: The End of Time)

The Hath were a race which allied themselves with Humans when they started to venture deeper and deeper in space. They helped mine the ores needed and create the first colonies.

They also 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 artifact that mythology 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 ended their conflict and agreed on peace, after the murder of Jenny by Cobb, the leader of the Human forces  (DW: The Doctor's Daughter)

Behind the Scenes

 * It was rumoured Hath wore 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).