Banggai cardinal aggression

leeloo82 · May 15, 2026

Hi all, so I was forewarned about banggai cardinalfish aggression once there was a mated pair. Got a group of 4 as babies from same tank at LFS (Freddy, Bonnie, Chica, Foxy - iykyk). The biggest definitely a menace. They're all at least 7 months old now but not seeing clear pair bonding behavior so possibly they're all same sex or still haven't sexually matured. Last night, Freddy the menace bit off half the tail of Bonnie the runt. Bonnie is now hiding together with the Red firefish in his cave (so kind firefish is not kicking him out of his cave). Will his tail heal? At this point, should I pull out Freddy and put him in timeout in the sump? Or put injured Bonnie in sump/QT til he heals? Or is Bonnie doomed to be picked on again later and I need to rehome him? Or rehome the aggressor? I was hoping there would be a clear mating pair and rehome the others. Or just wait this out? Thanks! Hard to see but maybe you can make out the injured tail in the dark cave. Other pic of happier times.

Tahoe61 · May 16, 2026

Once you have a mature Cardinal it might pair but the others are going to pay the price. A time out for the aggressor is pointless, it's what the fish does.
You are correct that the bullied Cardinal will likely continue to be bullied.
I would put the injured fish in the sump and hope for the best amoung the 3 left.

Good Luck.

RabidDragon · May 16, 2026

I bought two of these at the same time, at about 1 year old, one killed the other. The surviver has been in the tank the past ~4 years, doesn't bother the other fish.

Also something I've noticed about banggai cardinalfish that I haven't seen other mention, they appear to be entirely nocturnal in my experience.