LOL its probably not doubled but it can seem like it.Assuming you have a Polypterus senegalus they can have a fantastic growth rate as much as an inch to an inch and a half per month till they reach 7-9 inches then it tends to slow-Anne
ya i feed mine pices of night crawlers and he almost doubled in a month. but it has slowed down now. i think when ther very little like 3" or so they can grow fast if u power feed them but it will start to slow down