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Sudden tetra aggression?

3481 Views 5 Replies 4 Participants Last post by  Triport
Hi everyone, I'm new to the forum.

I have recently had a strange occurrence in my 29 gallon planted tetra tank.

In the tank, I have 8 neons, 6 serpae, and 6 black skirt tetras (plus some otocinclus and a pleco). All fish have been in perfect health. A couple of days ago I did a 30% water change and added a small dose of flourish excel. I left for a few hours, and when I returned all the neon tetras had badly damaged tail fins, some were almost completely gone. The serpae tetras had less extreme, but new rips in their dorsal fins, and a few of the black skirts had small pieces of their anal fins missing.

I'm thinking one or more of the black skirt tetras became suddenly very aggressive for some reason? I have seen no signs of aggression from any of the fish, however. All of the fish are still eating well, and actively swimming as usual. No further fin damage has occurred since as far as I can tell.

Can anyone help me understand what happened?
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Discussion Starter · #4 ·
Serpae tetras are known for being aggressive. Mine quit nipping as much once I got their numbers up to ten- plus then they won't bother other fish as much, being concerned with themselves. Even then there will be some fin-nipping within the group until they sort out their hierarchy.

I have noticed the Serpaes chase each other fairly often, but it never seems to result in fin damage. The Serpaes never go after the neons; or at least I have never seen them do it.

The neons are all healing up nicely now. However, I'm concerned that the next water change will trigger aggression. I guess I will just have to watch more closely next time and see what happens.
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