What happened?

[avilamillar]

Do you have a Lionfish and a Mantis Shrimp in that tank???

I do have a lionfish, not sure about the mantis.

i doubt it's a mantis, a mantis's attack is designed to kill, and is usually very effective. if you've seen it alive with damage, it is not a mantis. i'd suspect the other fish, but as mike said, it isn't the lion, because lions don't really attack as much as consume. i'd say the other anthias are to blame, sometimes fish refuse to play nice. if you can i'd separate the injured fish and see if things get better. it is also possible you were sold a pair of males and a female, which could prove problematic as anthias are haremic.

Well I tink that was the case. I was going to separate the fish but I just found it dead 5 minutes ago :( the cleaning crew were doing their job already.