dead fish

[Diesel]

I have 3 Red Serpae Tetras, 2 Tiger Barbs, 3 Gold Barbs and 1 Rainbow Shark in a 20 gal. tank.

A month ago I saw one Red Serpae Tetra lose some of the fin but I didnt see any signs of aggression.

and pretty much everyday I took some time to look at the fish and that Red Serpae Tetra was growing back his fins and looking good.

2 days ago I was pretty busy so I didnt have time to look at the fish and this afternoon when I check out the tank, in my supprise I dont see that Red Serpae Tetra anymore.

The only thing I saw is white fish bones under the tank(at first I cant even tell is a fish), it got no meat already , just white bones...

The barbs and the tetras are still trying to eat the bones...

Can someone tell me whats going on?
Its this normal?

 

[Menagerie]

[center:809df818df] Welcome to AA, Diesel! [/center:809df818df]
Fish will eat what's available including former tank mates.
As to why it died, there can be many, many reasons. One could be aggression--just because you don't see it, doesn't mean it isn't there. Barbs are semi-aggressive and are known fin nippers. This fish may have been chased around and died of stress. Tetras are generally a peaceful community fish, with the narrow-bodied ones being the most docile and the wide-bodied ones with a fin nipping rep.
~or~
It simply could have been it's time.