Dragon Adores the floor water bottle tunnel,not just to swim through,but it's a great place to sleep on too.
Just look at this close up below,it seems water immersed levitation is an extremely comfortable way to sleep,anchored barely by a couple of toes on one back foot.
This picture shows how capable Axolotls mouths are of swallowing a sideways turned goldfish whole.

Dragon was actually yawning at the time,long photography sessions can be so boring to an Axolotl.