I was recently asked question about whether they can keep guppies with axolotls
That’s a controversial issue. Some are of the opinion that you shouldn’t keep predators and prey in the same enclosure. Much like you wouldn’t expect to see a zoo where prey animals are kept with lions. However, in public aquariums, predatory sharks are kept with prey species.
It’s really a matter of size of the tank – whether the predators are sufficient fed, and the prey have enough space to live without being in constant fear.
Axoltols do not chase down prey – but they wait in ambush. So fish will not be living in constant fear if kept with axolotls. In fact, it’s the axolotls who may find themselves in danger – these fish could potentially attack the delicate gills of axolotls.
So, for a mixed species tank with axolotls, it’s a matter of the size of the tank – to allow sufficient safe distance between predator and prey, in particular there needs to be sufficient depth to allow fish distance from the tank floor where axolotls frequent, and there should be ample hides for your axolotls to get away from fish.
On another note, guppies are a tropical species, so they won’t be suitable to keep with axolotls that live in cold water.
I’m interested to hear what are other’s thoughts on this subject.