Usually, tetras are very peaceful, and people buy them because they are calm and hardy. Still, under some unmatched conditions, they become slightly to highly aggressive depending upon the tankmates around, a quantity of fish in the school, size of the tank, etc.

What is the most aggressive tetra?

The bucktooth tetra may not look like a piranha, but in the author's experience, it is more aggressive than one! Learn how to care for these beautiful but vicious animals for a truly fascinating tank in your own home.

Why are my tetras being aggressive?

When your Neon Tetra are stressed, they are highly likely to show aggression. There are multiple reasons that your fish can be stressed. ... Neon Tetra can also become stressed if their tank is too small and they are crowded. They can also become stressed if there aren't enough decorations in the tank for them to hide in.