Danio bullied

[Derekshatch]

I recently added bloodfin tetras to my community tank. I have some danios and the smallest male i think is getting picked on because it has never happened before. His fins are beat up and some scales are missing. What should i do? Should i wait and see if he recovers or move him?
He looks healthy and is eating and swimming around.

 

[Derekshatch]

Could it be fin rot?

 

[yeti79]

I've noticed new tankmates sometimes bring on aggression in danios. I would separate and medicate him for now until he heals. Might be a territory squabble, rearranging some of the decor could help.

 

[Byron]

The bloodfins are notorious for fin nipping so this could be the issue. How many are there in the group of bloodfins? And how many danios do you have? Kept in too small groups, any shoaling fish can become aggressive.

Normally, active fish like both of these if kept in sizeable groups will refrain from fin nipping because they are swimming and have enough of them. But there are no guarantees. And too few of either species will cause trouble of one sort or another.

 

[Derekshatch]

6 bloodfins and 5 danios

 

[Byron]

I should also have asked the tank size and the other fish species. If this issue only appeared after the bloodfins arrived, they are probably the source. Adding a few more bloodfins might help, but once this behaviour starts it never ends without removing the fish. They also will tend to bully (fin nip is one aspect) sedate fish (gourami, cichlids, slow-swimming tetras, etc) so if any of those are present the bloodfins need to come out. I've had this happen twice with other species in the same genus, it is in their DNA.

 

[Derekshatch]

I have 1 gourami, 4 platys, 3 corydorras, 1 pleco, 6 bloodfin tetras and 5 danios in 30 gallon.

 

[Byron]

I have 1 gourami, 4 platys, 3 corydorras, 1 pleco, 6 bloodfin tetras and 5 danios in 30 gallon.

Remove the bloodfins, return them if you can, this is not going to end well. You should increase the cories, at least five or six, preferably more, they are very social and less stressed the more there are.

 

[Derekshatch]

Why?

 

[Derekshatch]

What is not going to end well?

 

[Derekshatch]

I havent seen any fish being picked on i just guessed that it was the new fish, bloodfin tetras, that nipped at my one danio i havent seen amy other problems though.

 

[Byron]

What is not going to end well?

The nipping by the bloodfins. There is more to this than what we see, so I will try to explain.

Some fish species are naturally aggressive. "Aggressive" can mean many things, beyond attacking another fish. The bloodfins, species Aphyocharax anisitsi, are well know as fin nippers, a trait that applies to all the species in this genus. Keeping them in larger groups can sometimes contain the fin nipping to within the species. But any sedate fish like your gourami will be a target eventually, this is just how it goes.

But beyond the fin nipping which is physical aggression, there is the chemical signals fish use to communicate. Pheromones are read by others in the same species, and allomones by other species. Aggressive fish send out aggressive signals, and these will intimidate other fish like the gourami, and can be as damaging to the fish as can the physical aspects of the aggression. I have seen this play out, and in fairly large tanks too, like my 115g and my 90g with fish from this genus.