How Do I Stop Fish Aggression?

Hello everyone! It certainly has been quite a while since I posted a thread on this forum...

Recently, I’ve had an issue; which brings me back in hopes of advice! Of course I will try to be more active throughout the season. I hope you’re all doing well and staying safe.

With my situation, my smallest fish (featured in older pictures) had lost his scales about two weeks ago. I wasn’t sure whether it was due to the decorations (one giant piece of wood, centrepiece, a few live plants, some artificial, dragon stone, blue solidat stone, and a sponge filter- I have a few figures I got when going on a trip to China) or the larger goldfish in the tank. After noticing he was acting lethargic and not interested in his food, I put him in a temporary ‘hospital tank’ (which was a tub because I didn’t have one) for about two weeks (with the sponge filter) until he seemed ready and active enough to return to the tank.

As soon as I put him back, one of the larger fish (Mr. Orange-cheesy name) continued to chase and nip at his scales. I assumed this was some territorial issue, so I moved the decorations around in order to reestablish ground. After one day, I see the larger fish continuing to be aggressive (he seemed okay after moving decorations around). So tonight, I made the decision to put him the the other ‘tank’ to give space, in which I plan to bring him back in the morning.

I’m just concerned he’ll continue biting the smaller fish; as when he was in the tank, he scared the smaller fish (Mr. Koi) into hiding under ornaments and corners. He wouldn’t move out for a while...

What should I do if he continues? Mr. Koi came out to join my friendlier goldfish (Thing 2- from Dr. Seuss) once I separated them...

 

Either permanently separate them, get a larger tank, and/or add many more tall plants and object to act as line of sight breakers. Some fish also improve if there are other things to pay attention to and either can’t be harmed by the goldfish or are faster than it.

Do you have a picture of your setup?

 

Here is a current photo: It’s a little messy right now (I put more decorations and hiding spots ie the fake plant and plastic stone cave) but you can see Thing 2 and Mr. Koi... It’s a 55 gallon tank...

 

If this aggretion comtinues, separate them permanently. If not, be on guard anyway. I don't mean to scare you, but you don't want any fish to die becuase of a single mistake. Better safe then sorry. Wish you luck

 

Here is a current photo: It’s a little messy right now (I put more decorations and hiding spots ie the fake plant and plastic stone cave) but you can see Thing 2 and Mr. Koi... It’s a 55 gallon tank...

I’d definitely add more decor. Right now you have minimal sight breakers...try to up it so that you have at least one more object around the same size as that large rock and at least a handful’s worth of silk plants.

Keep in mind that if this does not improve things, separation may become necessary.

 

I’d definitely add more decor. Right now you have minimal sight breakers...try to up it so that you have at least one more object around the same size as that large rock and at least a handful’s worth of silk plants.

Keep in mind that if this does not improve things, separation may become necessary.

Thank you so much! Have a great rest of the weekend.

 

Thank you so much! Have a great rest of the weekend.

You too! Keep us updated on how things go.

 

Goldfish aren't like cichlids. They're descended from gibel carp, which are a schooling species, so they aren't territorial (maybe food aggressive); and adding more decor is pointless and might even cause more harm when they swim into it in panic. Thus, large, rough decor is not really recommended for larger fish and in a 55g, breaking line of sight is hardly going to matter. Maybe if you had small 1-2" fish, which you don't. And as you've noted, goldfish scales rub off easily. What's likely happening is the "aggressive" goldfish is actually a male trying to breed, and the hard decor might in fact be exacerbating the issue.

 

Goldfish aren't like cichlids. They are bred from gibel carp, which are a schooling species, so they aren't territorial (maybe food aggressive); and adding more decor is pointless and might even cause more harm when they swim into it in panic. Large, rough decor is not really recommended for larger fish and in a 55g, breaking line of sight is hardly going to matter. Maybe if you had small 1-2" fish, which you don't. And as you've noted, goldfish scales rub off easily. What's likely happening is the "aggressive" goldfish is actually a male trying to breed.

Great to learn some new things.