In recent tests goldfish have been proven to have a memory of up to 9 months, and Oscar's are more intelligent then them, give it a few months of owning yours and studying it and you will be shocked at its intelligence
I actually believe that there is a study that shows that while cranial capacity has a affect on intelligence it's not everything. Look at the parrots small brain, but it's capability to mimic words.Yeah, I see the Oscar fish has a big head.. They seems to be smart compare to gold fish.
I was thinking about adding another large Oscar.If you are in a hurry for an outgoing oscar, maybe add some dither fish such as giants danios.
I just added a convict today. Oscar is back to normal. I was having same issue
Ya my first Oscar. I bought him and some others around 2.5". He was fine until I put in 55g alone. Back to normal now. GL