Wesley Wong kindly transferred his last 5 Amur catfish to me in Aug 2015. They were ~5". Easy to feed. Very agile, boisterous. Eel-like flexibility and movement forward and backward. There is a definite enforced hierarchy and a difference in growth rates. Today the biggest are ~18", smallest ~12". Indifferent to tank mates unless it's a wels. Like to swim one right under the other with the one below pushing with its head at the one above, synchronously changing direction.
Them and their tank mates in 240 gal:
Them and their tank mates in 240 gal: