I picked up two Mastacembelus morii eels just under a year ago. They are one of the African spiny eels that are indigenous to the Congo area. I have not been able to find a great deal of information on them, but from I have found they max out at about 44cm. That is a little longer than you 12" limit you were looking for. So far, mine do not appear like they will be real heavy bodied fish at all. They are about 4" long when I got mine, and are about 8" long now. They like to burrow in the substrate a fair bit, but they come up and eat from my hand come feeding time. If I am in the tank arranging plants or something, they tend to pop up and get in my way nipping at my fingers. Fun and handsome things! The are almost big enough to get transferred into my main Congo Biotope tank. Let us know what you decide to go with. Good Luck!