Physically, the Nezu were humanoids with ridges running down the center of their faces and small horns above their eyes. Their bodies contained cardiopulmonary tissues. Compared to a Vulcan, they were less resistant to carbon dioxide poisoning and could become delirious if their blood was deprived of oxygen, and their their physical strength was many times less.
Their technology included metallurgical knowledge and combined high tech displays and controls with more basic-looking mechanical control elements. Their colonies used orbital tethers for transporting goods to an orbital space station.
The Nezu government included ambassadors.
They were encountered by the USS Voyager in 2373 when one of their colonies suffered from a series of massive asteroid strikes. It transpired that the meteors had been created by the Etanians as a method of driving out the Nezu. Fortunately, Dr. Vatm, a prominent Nezu astrophysicist, had realized that the meteors were not natural and had collected a large amount of information on the Etanian ship. He was killed before he could deliver the information but it was eventually given to Voyager, who used it to drive off the Etanians. (VOY: "Rise")