This morning I added a small school of Zebra Danio to my tank (about 7 of the little buggers) and since adding them at around noon (it's now almost 10pm) they've been shoaling at the very top of my tank right under the light.

I have a 45 gallon corner column tank, and the light is just a standard fluorescent that came with it.

When I turn the light off they all freak out and dart in different directions, as if someone dropped a rock right in the middle of them, and SEEM to end up in smaller groups wherever there's some light shining on the tank.

They've not gone deeper than 1 inch from the top of the water.

Should I be concerned or is this normal behaviour for Danios? I'm worried that when I turn the lights off to sleep the Danio are going to kill themselves by the time I wake up.

I'm more concerned about them staying at the top, what are the tank parameters?

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"Being ignorant is not so much a Shame, as being unwilling to learn".-- Benjamin Franklin

It's a 45 gallon corner column tank...

I have a school of 6 zebra danios in a 45 gal corner tank as well. They seem to like the top of the tank more and spend most of their time there. As long as yours are not gasping for air at the surface I would not worry too much. If you have only just put them in there then they are most likely a little stressed. Keep your lights off for a while and they should settle in a day or two. What are your water parameters by the way?

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45g pentagonal
4 Swordtails, 2 dwarf Gouramis, 5 Mollies, 1 Rainbow Shark, 6 Molly fry 6 zebra danios

88 gal Malawi tank
4 Yellow labs, 1 Baenshi, 2 Borleyis, 3 Trewavas, 2 Livingstonis, 1 Venustus, 2 Green Terrors

It's about 76-78 degrees Fahrenheit. Don't know about the pH level/nitrates/nitrites and all that but my Gouramis and Pleco are doing splendidly. They love it.

Did you add the 7 danios at once?I added my 6 danios over the course of 3 weeks.Not all at once. if you put the fish in all at once your ammonia while spike like crazy due to biooverload.

Your danios shouldn't be near the top of the tank.They like to swim all over the place.my danios swim everywhere and don't freak when the light goes out.In fact they get slower and its time for bed.Sleep while they swim sorta kind weird but they do.

Check your params immediatelly,the sudden adding of fish so quickly can be the cause of the problem.Also how did you accumulate them?or did you just put them in?it could be stress related.

My zebra danios spend a grand majority of their time swimming all around, but at the top of the tank. I do remember when I first added 3 they chased eachother around in circles for a couple days.

They stopped during the night, and now they're swimming at all levels all around the tank. They do seem to prefer to stay under the light, though, regardless of what depth they're at. I guess it was just new tank stress.

I bag acclimated them. Where you put the bag in the aquarium for 20-30 minutes so the temperatures match and put them in.

By parameters people are usually referring to the ammonia, nitrite and nitrate levels of your tank. If fish are showing any signs of illness or stress these are the first things to check. I think the freaking out is normal, they are just new to the tank and still jumpy, they will settle in soon. Hanging around the top of the tank can be a water quality problem so keep an eye on that.

It is good to add fish slowly but in a well established 45 gallon tank that is already stocked adding 7 danios all at once might not be a big problem.

What kind of pleco do you have? Check that you are not overstocked for your tank.

When I added my Danios they did the same thing. All parameters for the established tank were perfect. It's the nature of the beast, me thinks that in my experience, is perfectly normal behavior, especially for a column tank. If they're going from a rectangle to a column, they will need (and sounds like they have) time to adjust to the surroundings and different shape of the tank. Hope all is well.