Nothing could be worse. There are almost no fish at all that are compatible with axolotls for very long, usually because the fish will attack the axolotls and/or the axolotl will eat the fish. Plecos are the best example of a fish that is completely wrong with axolotls. Their nature of sucking on the sides of things, especially at the bottom of aquaria, means they often severely wound axolotls if kept together. There also aren't that many species of Pleco that have the same water temperature requirements as axies. So the answer is a big no.
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