Oscars grow up different depending on how much attention they get.
Many fish will be fine if you change the water frequently and feed them. They don't need friends.
An Oscar wants to see you a lot. You can spot the ones who got attention and those who didn't, and their happiness is important to their health.
This is Felix at 2 years old, and 10" long. The angle of the photo makes his head look small, but you can really see the fine scale development in the full image.
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He is over 11" now at 2.75 years and still growing.
I finally moved him from a 55 to a 75. He took it hard at first, but he's loving it now.