Schooling Fish Getting Picked On

[pirategrl]

I added 8 long finned zebra danios into my 55 gallon the other day.  This afternoon while watching the fish I noticed that one of them had his tail almost completely ripped off and one of his side fins as well.  He could barely swim.  I moved him into my 10 gallon quarantine tank and am treating with water changes and melafix.  But what happened?  I'm pretty sure that it was another danio that attacked him because they have been picking on each other a lot since I added them.  It's tank mates as of yesterday...
 
10 Neon tetras
6 corydoras
1 red fire gourami
1 golden bristlenose 
8 zebra danios
and then some snails and red cherry shrimp
 
After he heals up do you think it will be ok to add him back into the tank?  Is he OK by himself while he heals?
 

 

[PrairieSunflower]

It there plenty of plant cover? Something needs to chime in as I only have neons (as shoaling fish), but could it be they are insecure in their numbers?

 

[TallTree01]

It could well be the gourami. Is a red fire gourami a dwarf variant ?

 

[pirategrl]

Yes he is a dwarf.  That was my first suspicion but he (or she) is really mellow even my cories don't swim away when it swims near.  None of my neons or other Danios have any fin damage.  Just this one.  It's weird.  


actually none of the fish swim away from it.  

 

[eaglesaquarium]

Cover is actually a good suggestion as it will give the "omega" fish a place to go when being picked on too much.

 

[Wills]

It could be the Gourami as the Danios will swim in his part of the tank where as most of the other fish would generally be lower down.
 
The other thing I have found with Danios is sometimes in anything less than larger schools can cause serious infighting between these fiesty little fish. I would pop in some melafix and see how things go. Keep an eye for any particular dominant Danio and also an eye on the Gourami.
 
Wills

 

[pirategrl]

We lost a Danio yesterday.  The one in quarantine doesn't look too good either. I'm pretty sure it's not the gourami... he's just really laid back.  There is one danio that I see chasing the other ones and acting out.  I think that he may be the culprit.  The ones that are left have split into 2 different groups of 3.  One group swims up in the top and the other 3 stay hidden in the plants.  

 

[snazy]

Ammonia can eat the fins overnight. Test your water.

 

[Lunar Jetman]

Ammonia can eat the fins overnight. Test your water.

 
This is probably worth doing. You don't really have any fin nipping fish in there that I am aware of.

 

[pirategrl]

All water stats are good.  Ammonia 0 nitrite 0 nitrate not quite 0 but not 5 either.  API test kit.  The one in quarantine didn't make it and we lost another one this morning. So I packed them all up and brought them back to the store.  Their fins were ripped.. it looked like something was taking bites out of them.  All the other fish are perfect.  I have no idea what was going on....  My gourami is much happier now that they are gone and is now coming out of his little corner.  I'm beginning to think they may have been coming into his territory at night and that was when he was getting them?

 

[snazy]

I'm beginning to think they may have been coming into his territory at night and that was when he was getting them?

 
That's when predators attack normally. When the other's are asleep/vulnerable and don't swim away and hide.

 

[pirategrl]

If it was the gourami he better leave the rest of my fish alone!