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i purchased 12 columbian tetras (H. columbianus ) at the weekend and very nice they are too. But.........they've been beating the hell out of each other ever since. chasing each other round and nipping each others fins, biting off scales. most of them have chunks missing!! i know they're related to piranha but this seems odd considering they were in fine condition at the lfs. they are all about 2" long (max size)

could they all be all large males fighting? or am i not feeding them enough? although they do it even after they've just been fed.

could they just be establishing a shoal pecking order? or could there be a more serious cause?

thanks for any help.

What size tank are they in? Tetras kept in too small a tank usually display this kind of behavior.

it's a five foot 70 us gal tank!
although having said that it is filled to the brim with bogwood and plants, so there may not be quite as swimming room as you might think.

hmmm.....interesting

They are likely just re-assessing the pecking order. All should be at peace in a week or so. Hopefully you won't loose any in the meantime.

I have 16 of the same fish (also in a 75 gallon) and they are quite nippy with each other. They ignore the Loricariids though (which is a good thing for their long term survival in my tanks!)

thanks. that's what i thought. i'll keep a close eye on them and check if any wounds get infected.

It could also be that they're breeding.

Presumably your tetras were kept in tapwater at the LFS, and presumably you have soft, acidic water in your tank - if so your tetras probably think the rainy season is here.

Tetras are often triggered to spawn when they are moved to a new aquarium, and many tetras become highly aggressive during breeding time. Even normally very peaceful tetras such as neons become territorial and fight then.

well the thought had crossed my mind. they were kept in tapwater at the shop and my tank is very soft, but not quite so acid as i'd like !!!......................... about 8.

but that's a story for another post! do expect a "WHY WON'T MY PH COME DOWN" post soon.