Help please. I need advice with a territorial/aggressive fish

[Frostbyte]

So in my 20 gallon long aquaroum I have only glofish. It is a tank I set up to make my wife and daughters happy. In it I have 6 glofish danios (three green and three red) and 5 glofish tetras (one blue, two red, one orange, one purple and one green). The green glofish tetra happens to be the smallest of the 5 tetras by a fairly large margin but he is the terrirtorial/aggressive one. He seems to have taken over the middle of the tank and chases any tetra that dare swing through. This is not only disturbing the tetras but now the danios are no longer schooling. I have read various ideas online from removing him from the tank for a few days to a week and the introducing him back again to rearranging the decor in the tank to reestablish territories. What is the best way to handle this? It may be good to note that this was not occurring at all until after I added a new fish... but it wasn't a tetra, it was a danio I put it. So I just don't get it. But now when I look at the tank generally all I see is that green tetra right in the middle and everyone else on either side hiding. And in case you're wondering the tank is cycled and my ammonia and nitrites are zero. There is plenty of filtration and water movement. Plenty of oxygen. And enough decorations for hiding places but not too much to where it is over crowded. Any ideas?
The green guy is the problem. This is before I had added the new danio.

[morpheus]

all fish have their own personality. i dont think the addition of another danio really caused it. fish react most to others of the same species (competition for females for example). sometimes you just end up with an aggressive one in the bunch. usually 5+ individuals is sufficient for schooling, but you have space for more if you wish. the glofish tetras are a type of skirt tetra, which can get a little nippy with other fish. the larger the group the more any aggression can be spread out.

the methods you described are generally the first to try, and are what i would have suggested as well. removal for a small period and reintroduce, and rearrange the landscape a bit. can try adding more of the same species. if all else fails as a last resort, you can always return it to the store.

[ptran]

There is always a dominant one in any tanks. I'm thinking maybe don't do anything for a few days and let them sort it out. However, watch him closely. If he is too aggressive and start to kill other fish, you should remove him and re-introduce as mentioned.

[mredman]

Black skirt tetras can be aggressive within their own species or other community fish. By removing the most aggressive fish, the heir apparent may step up and become the next bully.

Tiger barbs have a similar personality.

There are no easy answers here.

Mike

[morpheus]

both above make good points. many fish have similar social structures. there will always be one dominant fish, and removal is usually the last resort for the reason both mentioned (it could set off a power struggle). as long as he is not killing other/injuring other tankmates, it is the way nature works.

i went through this quite a few times in my african cichlid tanks. when the dominant fish dies, chaos breaks out for a week or more as the rest of the colony sorts out the new pecking order. usually this involves me rescaping a bit so each fish picks its new territory. other times i added more individuals into the colony if one was being a bully.

usually with the semi-aggressive and aggressive species, numbers alleviate the tension. the skirt tetras fall into the semi-aggressive realm as far as tetras go

[ptran]

Looks like he took the biggest cave in the middle. You can try to throw in some more structure (rock, cave, PVC, deco...) to the left and right area, so they won't fight over the territory.

[Frostbyte]

Thanks for the replies everyone. I'm going to try rearranging the plants and such first. Then if all else fails I will move him to another tank. Problem is the other tank has cherry shrimp in it al I along with guppies and panda corys. I don't want him to start to terrorize the fish in that tank as well.

[mredman]

Thanks for the replies everyone. I'm going to try rearranging the plants and such first. Then if all else fails I will move him to another tank. Problem is the other tank has cherry shrimp in it al I along with guppies and panda corys. I don't want him to start to terrorize the fish in that tank as well.

Putting the aggressive fish into the cherry shrimp tank is not a good idea. The bully won't harass the shrimp - he will instead consume them.

Mike

[troy tucker]

The fish is just doing what fish do. As was said if you remove it. there will be another to step-up. IMO> the way to take care of the prob. is to add more or remove all. If you add more it will spread the aggression around. What I would do is get rid of all the glo tetras and find something else to take their place.

[morpheus]

Putting the aggressive fish into the cherry shrimp tank is not a good idea. The bully won't harass the shrimp - he will instead consume them.

Mike

i agree with mike here. cherry shrimp are ok with nano fish, but a larger tetra i would not do.

larger shrimp like ghosts or amanos could probably stand up to them, but cherry shrimp are a lot smaller. the tetra will also eat all the baby shrimp it can find

[ptran]

What I would do is get rid of all the glo tetras and find something else to take their place.

The wife and daughter might not be happy about that

[ptran]

i agree with mike here. cherry shrimp are ok with nano fish, but a larger tetra i would not do.

larger shrimp like ghosts or amanos could probably stand up to them, but cherry shrimp are a lot smaller. the tetra will also eat all the baby shrimp it can find

Yep fish love to snack on shrimps.