I have two zebras and four neon tetras in a four gal tank. I need to get rid of the zebra danio bully who's taking chunks out of the other zebra. Or I need to find a way to resolve its bullying. The pet store recommended the I freeze him as a humane way to euthanize, it doesn't sound humane to me.

What are my options?

You can use clove oil, put the fish in a small container with aquarium water and then slowly add clove oil the fish slowly become anesthetized/fall asleep, you can then either increase the concetration of clove oil and the fish will die or you can then take them out and cut off their head. The cutting the head may sound brutal to some but the fish in totally anesthetized at this point and wont know what happened.

Or if your are quick and feel comfortable some people will just take them out and cut off their head, again sounds brutal but truthfully if done right they instantaneously and is much more humane then many other methods including the freezer method.

I don't really think Capital Punishment is fair just because he is a bully, You could set-up a small tank for him to live in alone.

You could try and give him to someone who has larger fish who can handle themselves, in my time keeping fish Ive noticed that they tend to set a kind of pecking order maybe being down it a bit will chill him out.

My rec is to get a bigger tank. Honestly, a 4gal is not fit to inhabit much of anything beyond 1 Betta, let alone 6 fish. I am sure stress has much to do with his behavior.

Won't the fishstore let you give it back?
Give it away on craigslist... As the other post indicate there is no need to euphanize.
But if you feel you must or ever have to there are really great posts on the subject.
Here is one...
How To Humanely Euthanize Your Fish - Rate My Fish Tank

"Buddha in your tank"

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"Buddha in your tank"

agreed with the other posters, bigger or another tank would be the best solution without having to kill anything.

Your tank is overstocked which is adding to the stress. Fish will nip when stressed. Also, danios are a shoaling fish and should be in groups of 6 or more. They lose the aggression when they are in larger numbers. If you have a LFS or Craigslist try giving, not selling the fish. You can also check with any local aquarium clubs for takers.

He is not really a bully, he is just stronger than the other one. The stronger one will always pick on the weaker one, if you get rid of it and replace it with another one the same will happen again, it's what danios do. In a school of six or more the bickering is shared out and well balanced. If you keep only one it will either still be very shy and stressed or more likely start picking on the tetras. See if you can give both fish to some one else who can keep them in a school or get a much bigger tank.

I would not recommend 4 neon tetras in a 4 gal tank for several reasons but if you get rid of the two danios it might be just about okay. Live plants would help.

I have plenty of experience with danios and understand your problem.

These fish shouldn't be kept in groups less than 4 strong, if there are enough of them they won't pick on each other.

Just increase the number of danios so they the big one will stop picking on the little one.

I agree, but the tank you have is too small for a school of them. Are you able to get a larger tank?

it's been a while since I revisited the post. I gave the Danios to my sister that has a 30 gal tank and kept the four neon tetras. It's a four gal tank and is all it can hold. Part of the problem is that I'm new at this and the advice from the petshop attendant shared that three danios would be ok in 4 gal. tank. I now disagree. We live and learn. I'm getting a larger tank now. THanks for your wonderful advice.

We've all bin there! Glad it's working out. Do you plan to keep the 4 gallon running when you get a bigger tank? An easy plant like java moss would look nice and help to keep water quality stable.

Most of the time on posts like yours, the poster runs off and seems to stop reading as soon as the advice is unpleasant. I'm an unknown guy on the internet, but I still want to say that you showed solid judgment there, for what my opinion's worth.
We live and learn, if we're open to learning. I've been at this since the 60s, and I still learn constantly about fishkeeping - that's the fun.
I think we've all had bad advice from the 'well-meaning kid' at the petstore.
The first time a pet shop kid told I shouldn't buy a fish from the store, I was shocked. When he explained his reasons, he was right. I politely disagreed. He politely refused to sell me the fish, and I went home and thought about it. The guy was the best clerk I ever met.

danios are schooling fish they seem to do better in odd numbers.They need 6 to turn down the bulling.I agree don't kill the fish its not a criminal its probably stressed.Danios need at least 10 gallons minimual.I have 2 species of danios in my 10 and no bullying like this has happened and of course i have a semi-planted tank.They feel more safe if they have some space to call their own.

DO NOT KILL THE FISH JUST BECAUSE HE'S A BULLY.thats like saying everyone that bullys YOU should be killed.Its not right.

I think the poster resolved the problem already and is being responsible about his fish.

Yes, definately getting a larger tank, I'm thinking 20 g as I'm somewhat limited in space. I'm gettin interested in saltwater so it may be that, I don't know. Still doing researching and learning.

i've had zebras and tetras in the same tank and they didn't have to much of a problem... I have two possible solutions:
1)get more danios, i think they are nicer in groups of four or more.
2)the danio getting beat up is probably smaller, if he is, then i don't know what to do, but maybe you could set up a separate tank and put the smaller one in it. then buy more of the bigger-sized zebras for the bigger one and buy some more small ones for the small one? hope you get the problem solved!

Zebras are schooling fish, much more than Neons and need lots of other Zebras to chase. Your tank is just too small for schooling Zebras.