Titan-sharks or T-sharks were predators native to Titan. They looked like the sharks of Earth, but swam through the liquid methane lakes and breathed hydrogen or methane instead of oxygen.
After Titan was colonised to harvest methane, the Titan-sharks were discovered, even though it was believed that Titan would be incapable of supporting complex life. When a group of teenagers escaped from the Mnemosyne Cincture, they chose to hide out on Titan. While Dai and Sanjay were surfing on the lakes, Dai was attacked by a Titan-shark. Jamie McCrimmon was able to save him from being eaten. (PROSE: The Wheel of Ice)