Only one species was mentioned to guage this debate over. How would a 300gal not be enough to grow a monster larger than in the wild. An oscar in a 300, with ideal filtration/water changes/diet would have a helluva chance of outgrowing a wild one. It wouldn't have days of starvation if food items weren't available. It wouldn't suffer from runoff contaminants in its' water. I realize it's impractical to consider every species into this ideology. Especially if animals like pimas, giant silurid cats, gator gars, etc. enter into the debate. But, open a Monster Fish Keepers book sometime and see if you don't find fish larger than others you've seen before from expedition photos.