How long does it usually take for a O to reach full/adult size?

What you have got to realize is with many fish, they don't get to a certain size and stop growing just like mammals, they will carry on growing throughout their life. An Oscar reaches adulthood at approximately 12 months, but it could carry on growing for quite a few years after.

adulthood would usually be how many inches?

between 9-15 inch. 10" likely 15 less likely

I suppose an average size for an adult oscar would be between 10 and 12 inches.

just speaking from my one experience -they grow really fast in the first months. I brought mine home two months ago at 2 or 2.5" and they've more than doubled since then. i think I read somewhere on the site they grow 1" per month.

Mine grew fast upto 10" witin a year.
Now he's slowed down his lenghtly growth, and is getting fatter and more mature in appearance.
When he blows up when angry, he looks like a baseball.lol

The two that I have taken in are both growing really fast, I have had them around five months and the have atleast double in size since i got them

Noddy wrote:


Are you sure you haven't got a pufferfish that you have mistaken for an Oscar

Uhm, well i may be exegerating a bit, he looks a bit like a basebal, then.

smdsatx wrote:

depends on tank size and feeding regiment. with proper tank size, good water
condition and right feedings, 12 to 14 months old at 10 to 12 inches long.

an oscar can be considered an adult at 6 inches long upon reaching 14 months.
this usually happen with small tank and the fish survive the harsh living
condition.