It's their defense mechanism in the wild. I used to think it was near impossible too, but I saw many stories that said the same thing from separate people and occurrences. Keep in mind, that is if they are fed enough and are housed in a tank large enough to allow them to grow to that size. Most people that ignorantly buy a red tail catfish (which is pretty much everyone who doesn't have a massive aquarium in the thousands of gallons) don't keep them in tanks large enough and/or feed them enough to achieve this. However, as I have read many separate times now, this is a typical growth rate for these fish if housed properly.
