2 years ago #1
CuatiCoon
Guest

25 gallon tank, I HAD 2 neon tetras, 5 baby red
playtys, pleco, and a rainbow shark.
my husband bought me 4 zebra danios, and 4 of the glo danios. it was all calm, beautiful to watch, and they all got along. for about 2 weeks.
then, one zebra danio started attacking the other fish. in 2 days, the shark and both tetras were dead, eyes and fins already eaten. I watched the other zebras join the hunt and kill 3 of my playtys.
then they killed 2 of their own kind.
I bought 5 new tetras. they were dead in 3 days.

I can't add any other fish without them being killed.

please, please, help.

Posted on Tropical Fish
Answer
2 years ago #2
ziggy_h
Gold Member
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See if you can take the fish back sounds like you got a bad batch of blood craving danios are buy just a couple of bigger fish that can handel themselfs agenst the little devils

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2 years ago #3
gloman
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Hi!

Danios typically are not aggressive towards other fish unless their school is too small. They do seem aggressive towards one another, though, as the school develops a hierarchy of dominance through fin nipping and other "aggressive play."

Eight specimens in a school should be enough to keep the other fish safe from their aggressiveness. Since the glofish are genetically altered zebra danios, however, they may not school together as they would with a pure school. Fish in too small of schools may try to satisfy their own social needs by "aggressively playing" with the other fish, which will in turn stress those fish, sicken them, and potentially kill them. And yes, once a fish has passed, it does become food for the other fish.

Here are 3 possibilities:
1. Although fish species share general characteristics, just like people, individuals have different personalities. Bullies exist in the animal world just like with people. With bullies, sometimes it helps to remove them from the tank (like with a breeder net) for about a week, rearrange the decor, and then reintroduce the bullies back in. This breaks the dominance chain and allows for a different leader.

2. As counter-intuitive as it sounds, you could try increasing the school size (space depending) of both the regular zebras and the glo danios to 6 or more. Here is a stocking calculator to help not to overstock.
www.aqadvisor.com

3. Check your water parameters. Something in the water may be agitating the fish and making them more aggressive. Check for ammonia, nitrites, and nitrates. Was the tank cycled before adding fish? How often do you complete partial water changes? How big are they?

I hope this helps. Good luck!

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2 years ago #4
CuatiCoon
Guest

am I supposed to cycle the tank every time I add new fish? I only cycled when i started the tank three months ago. i cycled it for 2 weeks.

i thought of something that might be relevant. about a week after adding my fish, the water always had a green tint. After checking everything, i asked the clerk at a fish store what might be wrong. she told me i was feeding them too much. i fed only as much as they could eat in 1minute. once a day. she said the rule of thumb was if i saw a piece of fish food float from the surface, it was too much. she literally said 2 or 3 flakes 2 times a week was more than enough. i did it every other day. that was the week the danios started chasing and nipping the tetras. could they have been hungry?

after my first neon tetras died, i added 5 rainbow tetras, of course they all got killed, except one. last week i went to the store and got more zebra danios, thinking they just needed more in their school. i bought 5 large black neon tetras at the same time.

i pulled all the fish out and made them sit in bags floating in the water for an hour, releasing the new fish first. a different danio than the old bully immediately took off after the tetras. there are two left.

there are 13 danios in the school right now, with the pleco, 2playtys, and the 2 remaining tetras.

i change 20-25% of the water once a week, and feed them once a day again. the danios are about as long as the first two joints of your pinky. some of the new ones are smaller still. the black neon tetras were the size of the first joint on the pinky.

this is sad. breaks my heart every time i find another gone.
thanks for your help

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2 years ago #5
johnarthur
Blogs: 107
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This should answer your questions about the nitrogen cycle:
http://www.myaquariumclub.com/the-nitrogen-cycle- 1877.html

From your posting, the aquarium may be overcrowded or at least near its biological load limit. This may be one reason for both the aggression and fish losses. A crowded aquarium has little room for errors like overfeeding or a missed partial water change, and too many fish can overwhelm the nitrogen cycle.

You may also want to consider compatibility issues. For example, zebra danios are fast swimmers that stay mostly in the mid level of the aquariums. The tetras want to be in the same place, so conflicts are likely.

Probably, your aquarium would work better with fewer fish and fewer species. Before buying any more fish, make sure any water quality issues and aggression problems are solved. It may be necessary to rehouse the fish with the overly aggressive personality.

One workable feeding schedule is a staple dry food in the morning and a frozen then well thawed treat like brine shrimp late in the day. Try to feed no more than the fish actually eat in a couple of minutes, and use a turkey baster or small syphon to remove accumulations of uneaten food.

I hope some of these suggestions help. Please keep us all posted. If you feel comfortable doing so, you are welcome to join our forum.

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2 years ago #6
CuatiCoon
Guest

i can see how they would be overcowded. i must havea strange aquarium because the tetras stay near the substrate, and the danios at the top, unless diving down to pick at the tetras.
is it true that tetras are sensitive? perhaps i need to check the water again. if the tetras are ill, would that give reason for the danios to pick on them?

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2 years ago #7
johnarthur
Blogs: 107
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Aquarium fish are the descendants of wild species that evolved to cope with a specific environment. Even after countless generations of being raised in aquariums and fish farms, they retain the environmental adaptations of their ancient ancestors.

Since all aquatic environments are not the same, different aquarium species have different, and sometimes incompatible, needs and coping behaviors. Before populating an aquarium, all these things need to be considered. Although an aquarium is an artificial habitat, it should provide a reasonable simulation of the appropriate environment to keep the fish at their best.

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2 years ago #8
CuatiCoon
Guest

an update

I moved the danios to a 10 gallon tank. The original inhabitants of the 25g tank are happy and doing fine.
The danios are enjoying their private tank, although in my opinion they are still mean.

Thank you all for your help! I have learned lots!

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2 years ago #9
zebradanioexpert!
Guest

Well I know what our problem could be. Zebra danios are known as party fish. They usually do a lot better in groups or party's of 6 and up. For a 25 gallon tanks, I recommend at least 9 or 10. If you have a smaller group they do tend to become aggressive and attack other fish. So I reccomend to get at least 10 zebra danios.

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1 year ago #10
Makarov
Silver Member
Blogs: 1
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Votes: 4

I would honestly try and return the danios, or get maybe 3 more, its your choice. If you decide to keep them. Get some black phantom tetras or harlequin rasboras. Both very quick and strong. They could easilt take on the danios.

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1 year ago #11
gloman
Ace
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Hi, Makarov.

It's kind of hard to see, but in the top right-hand corner is a grayed out date. The last reply to this thread was made 4 months ago.

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1 year ago #12
Paul Roney
Wiz
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Tis cool gloman, we are all now in the loop on post dates, was just a newby error

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1 year ago #13
Makarov
Silver Member
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Oh for gods sake. Twice in a day.

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1 year ago #14
AlanaLovesDanios
Gold Member
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actually I had the same thing happen in my tank! only, the fish was already dead, I saw it, went to go get my net, I came back and all I see is my little golden babies ripping apart my other danio!!! I like freaked out. Ya, its creepy.

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7 months ago #15
gotn54
Guest

Your rainbow shark is the bad one, i raised danios for years and never had a problem. Did you actually see this happen. I will never have any type of shark with other small fish.
Try feeding your fish LOL

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6 months ago #16
Just a dude
Guest

Danios aren't considered aggressive but they do tend to play rough and pester other fish, if they do get agitated, it might be the ammonia, nitrate, or/and temperature levels.

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6 months ago #17
Just a dude
Guest

Your shark might be a fish bully, if it does bully several individuals they may gang up on the shark, see, fish are really smart and can arrange to get together, so buy a smaller shark, agressive fish of the same size tend to get along better then fish that are different sizes.

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6 months ago #18
Hi
Guest

Any zebra danios that aren't kept in a school, will often become stressed and may begin to display aggressive behavior towards other fish in the ...

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6 months ago #19
Heatherglo
Champion
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How big is your rainbow shark currently. Do you have a tight lid, as they are known for being jumpers, he will eventually need a bigger tank, topping out at 6 in. I have no doubt the danios turned.
But as he ages/grows destructive behaviors are sure to occur, both self inflicted and beyond.
Most danios with the exception of a few more dosile ones crave a current or they get bored and turn on others. Do you have a good flow going? I didn't know this about them, but another problem, very much like yours minus the shark was on here not too long ago, and an experience d member gave a very detailed description of why they need the current. But in a nut shell that was the meat of it

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6 months ago #20
nyleve
Champion
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Ahh, this post is over two years old. I don't think the op is around still.

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6 months ago #21
cuaticoon
Guest

It was awhile back. The danios were attacking the other fish. The rainbow shark was small at the time. It also had plenty of hidey-holes. I moved the danios to their own tank. The shark is in a 75g.

Thanks for all yalls input!

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