Rummy Nose Deaths In Community Tank - Why?

[Elly]

Two days ago I introduced seven rummy nose tetra to my 120L tank. I currently have in there: three rainbowfish, five rosy barbs, two Indian gouramis, and two dwarf golden eye cichlids (nannacara anomala).

They seemed absolutely fine, shoaling as normal, feeding normally, interacting with the other fish. This morning I've woken up to find the half-eaten body of one of them and the intact body of another sucked against the filter intake (external filter).

Any idea what has happened? None of the other fish were chasing them or being aggressive, and I don't think they are small enough to have been eaten by the rainbowfish (especially as the body of one is still whole). But they didn't seem sick either, and I only did a water change a couple of days ago so the water levels should be fine.

My only thought is that the nannacara are breeding and the male got a bit aggressive, but they've bred before and he's never shown much aggression besides chasing other fish.

Any help would be much appreciated.

 

[ultimatebob]

look at the fins of the diseased, and better yet look at the fins of the ones still alive. my suspicion is that the nanacara are not to blame, but the rosy barbs. though a peaceful fish in most books or whatever, rosies can act like a wolfpack, kinda like the tiger barbs. and rainbows can also be a bully even to other rainbows. smaller fish like the rummies can be an easy target. the nannacara should typically shun them away, but the rosies and the rainbows are fish that will chase.