My schooling fish are bullies?!?

[Karen B.]

I don’t know what’s wrong or if there is something in my water but my peaceful schooling fish always end up being bullies!

I started with White Cloud Minnows - apparently the most peaceful fish ever. Well, I had 16 in a 20 gallons high, sharing only with 3 orange mexican crayfish. One of the minnows was so agressive, within 3 days all my males had fins damage. I did everything I could, redecorated, put him in time out… nothing worked. I named him Jaws. I returned him to my LFS…. And another male took its place, terrorizing the whole group into a tiny corner of the aquarium. I ended up returning them all.

I bought a group of 12 green neon tetra. After few months, some got sick, some dies, etc. Ended up with only 7, and they were living in a 10 gallons. I think the space was too small, they kept chasing each other. I gave them to someone with a bigger aquarium.

I have had my Chili Rasboras for about a year. I started with 12 - all healthy and happy. Ordered 12 more - half of them were doa and I only had 3 left after quarantine.

Over the year, here and there I would lose a fish. I never saw any disease on any of them per say. 1 jumped out of the aquarium, some isolate themselves then die, etc. My group is now of 7 individuals- and now they are all scattered around the aquarium (20 gallons long, with 1 honey gourami, about 10 corydoras and 3 nerites snails), chasing each other. Each are hidind in their spot, coming out to eat, being chased away again. The honey gourami leave them alone.

My theory is that they are used to be in a bigger group and now don’t have that anymore? Or maybe there is too many males in the individuals left? I do plan on buying about 10-12 more but there is none available anywhere atm. And I can’t try breeding because I will be away for Christmas.

So until I can find more, is there anything I can do? I don’t want them to die of stress or something. I do have other aquarium (like a species only clown killifish 15 gallons aquarium with few shrimps)..  should I try moving them? Seperating them in 2 small group?

[meadeam]

Very strange indeed.  I have no idea, but I'll be interested if anyone else does.  I have black neon tetras, white clouds, and harlequin rasbora.  A school each all living in perfect harmony in a 29.  They shoal in a big bunch, and auto-sort themselves into schools when someone is around the tank.

[Guppysnail]

I’ve not kept either of these. However when aggression is a continuous issue outside of one or two individuals it has been my experience it is one of three things or all. Find the proper male female ratio and stick to it an imbalance can lead to conflict as you already hinted at. Also depending on their activity level they may need more swim space/elbow room so too many in a tank could be the issue. Do you have plants or plastic plants?  They might  need a playground with sight breaks and more plants/plastic plants (though I do recommend live) to make it a happier place for them. Hope that helps. Good luck

Edited December 2, 2021 by Guppysnail

[Karen B.]

On 12/1/2021 at 8:05 PM, Guppysnail said:

I’ve not kept either of these. However when aggression is a continuous issue outside of one or two individuals it has been my experience it is one of three things or all. Find the proper male female ratio and stick to it an imbalance can lead to conflict as you already hinted at. Also depending on their activity level they may need more swim space/elbow room so too many in a tank could be the issue. Do you have plants or plastic plants?  They might  need a playground with sight breaks and more plants/plastic plants (though I do recommend live) to make it a happier place for them. Hope that helps. Good luck

This is the tank. All real plants/rocks/wood except 1 ceramic hide. 
I have to create some protected place for my floating plants because they all get by the filter and end up brown/dying. Will do so this weekend.