Ok, I'm going to end this once and for all.
Today I called the Aquarium in The Indianapolis Zoo
Now the guy I talked to asked what Variety of Pacu I had.
He said that there are 2 main types of Pacu.
Colossoma Brachypomum - Red Belly Pacu also known as Silver Pacu.
and
Colossoma Macropomum - Black Pacu
I have Colossoma Brachypomum.
Colossoma Bracypomum size Max out at 18" to 20"
He said that RED BELLY PACU do most of their growing in the first 2 years of life.
After that they grow about 1/3 of their size every two years.
A Red Belly Pacu's life span is right around 10 years.
He told me that my Pacu's have more than enough space right now and they will continue to have more than enough space for the next couple of years.
He said that when they grow out of the 250g. The 810g tank that I'm going to put them in will be "more than ample" To hold them for the rest of their lives.
He said I have and will have the right tank sizes to keep these fish very happy and very healthy.
He gave me a couple of web sites that will "back up" the information given.
Mongabay
Aquaria Central
These are the cold hard facts, from a professional.