My Oscar fins are hurt

[Dcheung06]

I’ve had my Oscar for around 2 month and he’s grown to be over 4 inch now. I share my tank with my brother and he added a firemouth cichlid, redtail shark, crayfish and a angelfish.

Right now I’m trying to figure out which one of these fish is the fin nipper can you guys help me?

PS also have a pleco

 

[Rocksor]

post a pic of the tank

 

[duanes]

I Hope the tank is over 6 ft long as all those fish will all get fairly large and out grow anything smaller.
The oscar (maxes out between 12-15") will at some point eat the crayfish, I've had 10" oscars eat 6 " crayfish.
Just another FYI, the oscar, the angel, are South American soft water fish, red tail prefers soft to neutral water. (pH in the 6 -7 range)
The fire mouth (from Mexico) averages about 10" max length (a friend had an old male @12") and they come from and prefer hard, alkaline water, pH around 8.
If your tap water is neutral, they should all be fine, but a couple degrees pH one way or the other can determine who stays healthy long term or not.
You can find out by calling your water provider, or sometimes it on the info in your water bill, or better yet.....use a test kit yourself.
One like the one below.