They can grow up to be around 12" I would never keep one in less than a 75 gal thoughI'm currently searching for gulper catfish. Apparently 1 should be ok in a 55 gal (they don't seem to need much room). They might not be very colorful, but they seem pretty interesting. Check out some you-tube vids on them. I can't wait to get one and hand-feed it prawns!