Fish

I know everyone says no to fish in axolotl tank but I know that there has to be one fish that can go in the tank

lol. There ARE fish that can go in a tank with an axolotl. There are NOT fish that can co-exist peacefully with an axolotl. Either they won't be able to tolerate the cold water, they'll be big enough to hurt the axolotl, or they'll be small enough to get eaten. If it's big enough to definitely not get eaten, it will either nip at the axolotl's gills or it will produce enough waste to make it really hard to keep the tank clean and the parameters acceptable. If the fish is small enough to not be a danger to the axolotl, there is a good chance it will get eaten or at least bitten up pretty bad. You can put guppies or certain danios in an axolotl tank. If you are ok with the fact that they might get eaten, go for it. If you put them in with the intention for them to get eaten, even better. Just be cautious if you get them from the pet store and put them directly in. There's always the chance that they're carrying a fungus or bacteria that could kill your axolotl. If you really want to do it, it's best to quarantine the fish for about a month before you actually put them in with your axolotl. Or do what I would do and get them from someone you know. My sister has free-breeding guppies. I know they're clean. I might put a couple in my axolotl tank just to see what happens. lol