GloFish and Zebra Danios not getting along. - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 2 Old 05-05-2012, 03:26 AM Thread Starter
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GloFish and Zebra Danios not getting along.

Last week I got 5 glofish, and 4 of them died. I let my last fish be alone for about 4 days, but felt like it was stressing him out so i got him 2 regular zebra danio tank mates. One of them is rather large, and the other is about the same size as my glofish. I'm assuming the large one is a female and my other two are males. The moment i got that larger fish into the tank my glofish started acting aggressive towards her.
First he was rubbing all over her, which i thought maybe he's just "making his intentions known" (wanting to spawn with her) But then he started chasing the other Danio around- and I can't tell if he's nipping at its tail or just chasing him around. I know that danios are playful fish, but they are not responding in kind. If they chased him back i'd feel more like they were playing, but they are trying to hide/get away from him a lot. Often all three of them get into this frenzied wrestling match and flip over each other- which really concerns me.
When i had the 5 glofish before, none of them acted like this (and i even got two of them to spawn and am now taking care of their orphan babies )
I tried all manner of separation, but the glofish is just being mean! When i tried removing the glofish, the other small Danio decided it was his turn to bother the poor lady. I took her out and put her in a breeding net, just so she could relax and get some time to herself. But she jumped out of it twice and is a real pain to catch, so i didn't want to try again.
I turned the tank lights off, and covered it partially with a towel so it was dark while i still worked in my office and it seems to have calmed my glofish down a bit. I check every now and then to see how they're getting along and he still chases that little Danio, but doesn't seem so rough and tumble with the bigger one. But when i turn the lights back on he goes right back to it.

They are in a 10 gallon tank that is still in the early stages of its cycling. The nitrite levels are -just- starting to go up after the ammonia spike. The tank has been set up for just over a week. Is he acting odd because of this? I know that ideally they need a lot of swimming space, a 20g would be more what they need- but i don't have a place to put a 20gallon tank. Also i know they are good in a school of 6+ but i don't want to go spend more money on fish that are going to die during the cycling. I own a 30gallon tank that is in storage under my stairs, but as i said before i don't have space for it; and it's a lot of work to set up such a large tank on a hope that my fish is going to behave.

Am i correcting in thinking he wants to spawn with her, or is he just being rude and aggressive to the new people in his territory? I read that leaving them alone can make them territorial, and that's part of the reason i decided to get him some friends so that didn't happen. Should i have not gotten them? Should i take them back? Should i wait it out until he asserts his dominance? Should i do a water change and hope they spawn and do their thing? Will his aggressiveness pass? He is just so rough with them I'm afraid he's going to seriously injure, or kill, them.
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post #2 of 2 Old 05-05-2012, 09:25 AM
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First thing. welcome to Tropical Fish Keeping forum.

Now to your question. There are a couple of problems here. First is that this species [the Glofish is a modified form of the Zebra Danio so the same "species"] is a shoaling fish, meaning that it lives in large groups naturally and therefore must be kept in groups in an aquarium of sufficient size. Most will consider 6 the minimum for the "peaceful" shoaling fish, but the more the better.

That brings us to size. A 10g is not sufficient space for a group of this species. They are very active swimming fish, and they need space, at least a 24-inch tank at minimum. A group of say 7-8 in a planted 24-inch tank would be fine (or should be, one can not assume fish behaviour but only assume what is "normal" for the species).

And here a quick word on behaviour. When shoaling fish are not maintained in sufficient-sized groups, trouble frequently occurs. This is also an issue if the tank space is too small (to the fish). Both these environmental factors affect fish considerably. You can read more in an article on stress:

In a 10g i would stay with the "dwarf" species of which there are several in the cyprinids and some in the characins. Many of these are in our profiles, under the second tab from the left in the blue bar across the top of the page. When the name is used the same in a post as in the profile it will shade, as it did above, and you can click on that for the profile.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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aggresive fish , breeding , glofish , zebra danio

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