- You may be looking for the mutated Atlanteans.
The Fishmen were short humanoids, less than four feet tall. As their name suggested, they were fish-like in appearance, with green scales, webbed feet, gills around the neck and waist and bulging eyes. Though amphibious, they needed to spend much of their time in water to survive. The Fishmen had small tendrils around their body, which they used to telepathically communicate. The Fishmen also bred quickly, a trait that was useful to the Voord. (PROSE: The Fishmen of Kandalinga)
When the Voord came to Kandalinga, they enslaved the native Fishmen as workers. The Fishmen were kept docile telepathically and were kept in concrete pits filled with water when not used. The Voord used them to try to create land, eating them when they had no more use for them. They planned to wipe them out after they were done. Though they attempted several uprisings, thousands of Fishmen were wiped out to put them in their place.
Many thousands of years later, the First Doctor came to Kandalinga. When he saw the Fishmen, he was curious about why they were there and waited to see what they were working on, which allowed him to be captured by the Voord. Later, when he was taking the Voord leader to see his ship, he was able to stop the Voord's leader's telepathic control. The Fishmen were able to overpower the leader, then rose up against the Voord to take back the planet. (PROSE: The Fishmen of Kandalinga)