"Max size of a pacu is 12'' and they can be kept in a 75gallon for life", by petco, petsmart and walmart. Funnily enough, there is a public aquarium in my metroplex with some of the biggest pacu in the world. The biggest one is about 4ft long.
"ID shark only grow to 8'' and will be fine in a 55 gallon for live", many time by petsmart and petco employees. And I've had 3 of them in a 600 gallon tank before and they grew from 4-5'' to 2 ft in over 2 years.
the "silver arowana can be kept for live in a 100 gallon" was from that biggest misinformation show that just finally got cancel, Tanked.