I've always belived that was an issue of not having enough in the school but I was at a store the other day and noticed this serpae tetra nipping the fin of a congo tetra 10 times his size. The little dude was a real pest and there were a whole group of them in the tankWhich Tetra should be avoided? Which ones are a very aggressive fin Nippers, plants, etc.. for example red eye tetras are these good or bad? What about serpae or columbian tetra???
These fish will also mangle, injure, kill smaller weaker fish. Even if they are not trying to.Buenos Aires are plant eaters.\\
My aquarium is full of neons and they don't bother anything in the tank. The worse is that one neon would ram another neon however never touched or even look at a shrimp. The shrimp may be swimming fight in front of it or even holding on to a micro pellet which the neon eats sinking down right in front of the neon's mouth and still nothing.I have owned neon tetras that nip at everything in the tank, and totally tear up and eat shrimp. Oh, the Carnage! I was told they would not do this by many people who kept them with shrimp, etc. So I've come to learn that any fish is a possible suspect in nipping and killing. I started a thread about this a year or so ago, when my neons tore up ghost shrimp and nipped and rode the tail of my betta.
http://www.plantedtank.net/forums/88-shrimp-other-invertebrates/803354-neons-kill-shrimp.html
Definitely neons. I was surprised they could do that too. I think someone mentioned the health of the neons as a factor in aggression on my killer neon thread. The healthier, the deadlier? Just don't know, but they were nasty little buggers.Could they have been Cardinal Tetra which look identical to a neon tetra? Its technically a cousin to the Neon Tetra?
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It's so funny, because mine do exactly what yours don't. My rummies shred the tails of bettas, chase behind them, eat from the top and bottom or anywhere there is food. They are serious fin nippers and super fast and furious. They haven't nipped at my Gourami or Angelfish however. But long finned Bettas are now short finned. I am re-homing the betta in the tank because of it. Nothing but Mountain Minnows has worked with my Bettas long term.The one tetra I think I've never seen a single bad thing about is rummy nose tetras. Mine simply school and swim back and forth the front of my 55. If another fish is in the way, the school will turn around and swim the other way. They are by no means teratorial and when eating mine are the only fish, out of neons, cherry Barb's, danios, and angels, that don't swim to the top of the tank to fight for food, they wait for the food to fall and eat that.