[tang daddy]

My experience is crabs will eat dead fish or injured not moving fish.

The only other inverts fast enough to catch fish is mantis.

If you haven't added any new livestock recently then it's possible that they didn't die from a disease. It is really weird that the fish would just die overnight tho... And if your other fish are Mia that's even more unexplainable.

I have had fish for a year or 2 then slowly get more and mood skinny almost anorexic then eventually die. Recently I bought a few new fish and mysteriously they stopped then 2 days later dead. Only the new fish passed while the rest are completely fine.

Sorry for your losses!