Mexican Dwarf Crayfish vs Pleco

[Guybeaux]

I've had a nice Mexican Dwarf Crayfish in my 26 gal tank sharing the bottom tank with a couple of small Cory Panda.
I started to have issues in my 46 gal Discus tank.  My 3" Pleco started to bug the Discus, it developed a taste for their mucus. I've switched the Pleco with the Cory Panda. For a couple of days the Pleco didn't seems to care much for the Crayfish but now it's nowhere to be seen.  Is the 3" Pleco compatible with small Mexican crayfish?

[Nyx]

I kept CPOs (Mexican dwarf crayfish) for years. They are usually quite hardy and do not tend to bother fish or plants. Mine always lived with a 3" clown pleco and the pleco never bothered the CPOs. My pleco wasn't in the least agressive, though.

Your CPO may have moulted which could be why you aren't finding him. After they moult, they are quite vulnerable until their shells harden so they will hide to keep safe. If you haven't seen any trace of him, I would think that he's moulted and hiding. However, if he doesn't have a "hide" of some kind, he'd be quite susceptible to being eaten by other fish without a hardened shell. Aslo, if CPOs get stressed out or water parameters aren't correct for them, they can have an incomplete moult which usually results in their dying. Hopefully, he was just hiding after a moult and he's shown up by now.

[Guybeaux]

Good news I found him back. You're right it most have been moulting and very well hidden spot.
I keep mini glass 3" decorative bottle in my tank and I've seen my crayfish moulting in it.
I've seen him almost walking over my Pleco and they've ignored each other.

Would anybody have any idea why my vivid dwarf Mexican orange crayfish turn almost grey with darker spot within a couple of months.
He looks more like a St-Laurent river crayfish.
I feed him crayfish food and once in while his tank gets frozen brine shrimp.
Water is at 28c