The Aquarium Tank Wagons are closed wagons with clear sides and are filled with water. They are rolling stock used for transporting live sea animals such as sharks, octopuses, fish (like Dory, Marlin and Nemo), ect. They were only seen in the books Down at the Docks and Thomas and the Shark.
Thomas first saw these wagons while he was looking for a way to help with preparations for the ocean show at Tidmouth. He admired the octopus in the first one, but was frightened by the shark in the second. Salty who was coupled up to the tank wagons told Thomas the two sea creatures were meant for the aquarium. Percy puffed pass Thomas and Thomas tried to tell him about the special cargo Salty has, but Percy was in a hurry and puffed off quickly. Percy puffed up to the tank wagons, and was also frightened by the shark. He was so frightened that he caused a huge accident. After Thomas helped clean up the mess, he went with Salty to look at the wagons when the shark winked at him.
The tank wagons are conflats with added water tanks.
- Wooden Railway (discontinued)
- Take Along (discontinued)
- Take-n-Play (discontinued)
- Adventures (discontinued)
- Motor Road and Rail
- The aquarium tank wagons are seen in the twenty-second series episode Forever and Ever as part of Gordon's dream pulled by Rosie.
- One of the aquarium tank wagons is seen in the twenty-third series episode The Sodor Fish being pulled by Thomas as he takes Dory, Marlin and Nemo on a tour around Sodor.
- One of the aquarium tank wagons is seen again in the movie, The Secret of the Cave Treasure being pulled by Nia as she takes Dory, Marlin and Nemo on a hunt for Thomas and Ashima.