Let's start with the problem with the fish ...
Usually,an occasional fish snack won't hurt an axolotl. Exceptions:1. if the fish has parasites/illness, some of them can infect the axolotl. 2. Some fish are physically dangerous to eat, like many catfish. They have spines in their pectoral gills that lock into place when something tries to eat them. An axolotl can die from eating them.
A more common problem with fish is that the fish eat the axolotl, or at least, parts of it. Those pretty frilly gills are a tasty treat for the fish. Plecos will suck on the mucous coat of the axie, causing harm.
So, a strong recommendation is to rehome the fish or bring them back to the fish store.
Next, cycling the tank. THIS IS VERY IMPORTANT. Right now, ammonia is building up in your tank.To save time on finding links, I'm copying someone else's post.
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The cycling process can take from 3-6 weeks. For your tank to be cycled, the beneficial bacteria needs to be present to break down the Ammonia and Nitrites into Nitrates. Ammonia and Nitrites are lethal to Axolotl and are produced from your Axolotls waste and decomposing food. Nitrates are a less toxic by product.
For more details on cycling read these articles:
Caudata Culture Articles - Water Quality
Caudata Culture Articles - Cycling
How to Cycle a Fish Tank
Cycling is one of the key factors of keeping your Axolotl healthy, as well as temperature.
Read these websites fully for more information on Axolotl care:
Axolotls: The Fascinating Mexican Axolotl and the Tiger Salamander
Caudata Culture Axolotl Articles
Take pictures of your tank if you want any opinions on your setup.
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Tell us everything about your tank. You can guess as to the size or use body-parts - how man hand-lengths long, wide, high, and do you have big hand or small ones? What brand/model filter? What else is in the tank tank (decorations, substrate, etc.)?
Are you using a water conditioner? What kind?
What other advice were you given by the store? I suggest verifying everything with us. We aren't trying to sell you something and do want to help you keep your axolotl healthy.
