Unknown Fish Aggression

claylacey · Feb 10, 2026

I have an unknown bully in my tank as I haven’t caught who the culprit is that’s attacking my fish. I had a beat up red firefish that died last week. My newest addition, a yellow/purple wrasse, and my purple firefish have both had their tails messed up and keep getting attacked by an unknown fish. Here is my population in my 180 gallon. Any ideas who my suspects could be? Thank you!

Blue hippo tang (biggest in the tank)
Convict tang
Bristletooth tang
Tomini tang
2 blue chromis
Yellow/purple wrasse
Pair of gladiator clownfish
Purple firefish
Pajama cardinal
Bicolor blenny
Cleaner shrimp
Various hermit crabs

Jay Hemdal · Feb 11, 2026

claylacey said:
I have an unknown bully in my tank as I haven’t caught who the culprit is that’s attacking my fish. I had a beat up red firefish that died last week. My newest addition, a yellow/purple wrasse, and my purple firefish have both had their tails messed up and keep getting attacked by an unknown fish. Here is my population in my 180 gallon. Any ideas who my suspects could be? Thank you!

Blue hippo tang (biggest in the tank)
Convict tang
Bristletooth tang
Tomini tang
2 blue chromis
Yellow/purple wrasse
Pair of gladiator clownfish
Purple firefish
Pajama cardinal
Bicolor blenny
Cleaner shrimp
Various hermit crabs

Nothing in your species list would be a *confirmed* aggressor IMO. However, fish don't always behave like we think they should. You can obviously rule out the fish with damage....

Finding the culprit can be a bit difficult - you may never see an actual "hit", when you are in the room watching them, the fish may "play nice". Look for fish shying away from another one, or if one fish makes a "false run" at any other fish. Another trick is to set up your phone to video the tank and then leave the room. Sometimes, when you review the video, you can figure out who the culprit is.