zebra danio ate my longfin danio's tail

[Tostada]

I've got 3 danios (1 longfin female, 1 zebra female, 1 zebra male). The only other thing in the tank is a betta that ignores everybody and 3 ghost shrimp.

The longfin is the largest. The male is the smallest. When I first put the longfin in there, the zebra female kept chasing it around and nipping at it. It didn't seem to do any damage, but this morning when I got up the longfin was missing most of the bottom half of its tail. But now things have turned around, and the longfin has been chasing the zebra female around all day.

Are they just going to keep trying to eat each other? I noticed on fishprofiles.com it says danios will nip at longer fins, but none of them have ever bothered the betta.

 

[lmw80]

I am not sure if this behavior will continue, however, danios should be kept in schools of at least 5. Maybe that's why they are acting so aggressive.