i sort of already told you all of this on irc buuuuut
fish are cool but axolotls are cooler, because they're like having fish and having lizards at the same time. plus, they're hella easy to care for and severely cuter than fish (because they don't have the cold dead stare that fish do, instead they have cute little dot eyes and smiley faces). also they live pretty well together, so you can get more than one. also unlike some aquarium setups where you have to have a pretty huge aquarium, two adult axolotls can be kept in a 20 gallon tank which isn't too big really. and since your requirements are that it has to be something that can be left on holiday, it would be very easy to just have someone come 'round and throw a bit of food in there for it every few days or something. the only downside is that they aren't always easy to find, but i'm pretty sure there's several breeders in the UK so if nothing else you could have them shipped (this is what i did, because there were none for sale near me so i just paid to have one shipped from elsewhere in the US)
just please learn from my mistakes and be very careful to sort through the gravel (or use something other than gravel) because even if the gravel is in general very large, there's still the possibility that a single piece would be big enough to swallow and trust me, they will
