Lager Oscar chasing other Oscar

[Sharanraaj]

I have had two oscars( 10-15cm) in this tank for 2months with no problem. They swim and eat together. They often lay beside each other at night. Two weeks ago I added 5 silver dollars into the tank. There was no aggression. Two day ago I noticed that the larger Oscar was chasing the smaller one. No lip locking. During feeding time they are ok . What could cause this?

 

[BIG-G]

It’s just normal oscar behavior.
They are just generally territorial and will assert dominance.
Usually once a hierarchy is established they calm down a bit.
Just keep an eye on it to make sure the dominant fish doesn’t take it to far.

 

[duanes]

It’s just normal oscar behavior.
They are just generally territorial and will assert dominance.
Usually once a hierarchy is established they calm down a bit.
Just keep an eye on it to make sure the dominant fish doesn’t take it to far.

Agree with BIG-G, because when you added the SDs, you altered the normal tank hierarchy, and reduced the most important available resource (sufficient space).
When adding other fish, the dithers are not the ones the territorial shrinkage oscar will care about, but the its cichlidic space, hence one becoming more jealous of the amount of what's there, or now isn't.

 

[FINWIN]

Nice clean tank but as your Os grow that space issue is gonna get worse. I see you have clown loaches in there too...gonna need a whopper tank if you keep 'em all!

 

[LBDave]

Agree with BIG-G, because when you added the SDs, you altered the normal tank hierarchy, and reduced the most important available resource (sufficient space).
When adding other fish, the dithers are not the ones the territorial shrinkage oscar will care about, but the its cichlidic space, hence one becoming more jealous of the amount of what's there, or now isn't.

Interesting you bring up jealousy. I had my 2 8" oscars in with 2 pbass. The oscars would sort of defend against the pbass and visa versa but no real fighting for space. The 2 oscars were fighting too much. Remove one which always flared gills (all his life, like a complex). Then the remaining started to bug the bass pretty bad.
It's interesting how adding or removing fish and change or upset the balanc.

 

[Sharanraaj]

Should I try remove the more dominant Oscar in quarantine tank for a couple of days then reintroduce them after rearranging the tank
The second someone walks close to the tank or if the lights are on, both beg for food together. There is no aggression during this time.

 

[LBDave]

Should I try remove the more dominant Oscar in quarantine tank for a couple of days then reintroduce them after rearranging the tank
The second someone walks close to the tank or if the lights are on, both beg for food together. There is no aggression during this time.

It’s common that oscars can do this. Aggressive at times and then swimming together. This is common Oscar behavior.
A larger tank will help. I have target fed to make sure the less dominant Oscar maintains a good size. That can help.
Ultimately you may find that the behavior will not end unless they are split up.
At least that’s what happened with me.
Oscars can also vary with their behavior From individual to individual. With any fish if aggression starts to happen a lot or all the time it’s unsustainable. The picked on fish can’t sustain. It’s also not enjoyable for the fish keeper.

 

[Stanzzzz7]

Tank looks very small for one Oscar. Not surprised two are fighting. You need to choose a bigger tank or a smaller more peaceful species.

 

[xraycer]

Tank looks very small for one Oscar. Not surprised two are fighting. You need to choose a bigger tank or a smaller more peaceful species.

A single Oscar could potentially get to nearly half the length of that tank in about a years time.

 

[Sharanraaj]

It’s a 3x2x2 feet tank. Will be upgrading the tank in a year time