Tret's species
Tret's species was a humanoid race whose people had suffered from an epidemic caused by a mutagenic virus originating from the Loque'eque homeworld. 

Tens of millions of people on this species' homeworld were infected with the mutagen. To prevent the virus from transforming the entire population, this species resorted to genocide, to prevent the destruction of their own race. 

This species began studying the mutagen in the 2090s, but was unsuccessful in its attempts. They felt that the only course of action against it is to neutralize the outbreak. This was accomplished by putting a quarantine on the Loque'eque homeworld, and incinerating any alien who landed on the planet and became Loque'eque. ()

People 
 List of Tret's species

Background information 
In the first draft script of "Extinction", the name of this species was "Aurigan". However, the species was unnamed in the final draft of the script and isn't named on-screen either.

A note in the script of "Extinction" (both the first draft and the final draft) specified that the members of this alien species, which is not named on screen, were to be portrayed using "light prosthetics".

In the first draft script, Phlox stated, in the episode's final scene, that the Aurigan Health Authority had devised a plan to sterilize the entire Loque'eque homeworld.

nl:Tret's ras
Unnamed species