The Tesnians were a humanoid species native to Tesnia in the Alpha Quadrant. The Tesnians were spacefaring since at least the 22nd century. Tesnians required boron gas to survive. (ENT episode: "Shuttlepod One")
On November 9th, 2151, first contact was made with Humans when a Tesnian starship encountered United Earth starship Enterprise (NX-01). During the docking maneuver, the Tesnian ship crashed. Enterprise returned its crew to Tesnia. (ENT episode: "Shuttlepod One")
On March 13th, 2163, Tesnians were among the non-aligned attendants of the Deneva Conference convened in response to the Mute crisis. The Tesnians reported the loss of one of their colonies, including its 93 settlers, their belongings and buildings. Along with the other attendees, the Tesnians resided in an encampment at the edge of Deneva's compact capital city. The Malurian Dular Garos had secretly influenced the Tesnians to participate, on behalf of his Orion allies. In April 2163, a Tesnian listening post detected a large number of Vertian ships heading in the direction of USS Endeavour, and warned the Federation ship about them. (ENT - Rise of the Federation novel: A Choice of Futures)
Rise of the Federation: A Choice of Futures author Christopher L. Bennett tentatively identifies the unseen Tesnians with two unnamed dignitaries participating in the Coalition of Planets talks on his A Choice of Futures annotations page.