I had one piebald walking catfish in my "care" for about 6 years and it reached 16" and was quite thick. It was an invalid though - lacking one pectoral and the caudal fin altogether. Bad genetic hiccup.
Not sure why it died. I thought they'd live longer than that but again, inferior genes most usually result in short lifespan too. I bought it in Toronto in 2009.
I can't think of any other readily available piebald catfish.
Anyone?