It will take him a month or 2 to warm up to you, But after that he will be beggin your for some eats. Thats how most of my Vieja/Paratheraps have been. Shy, and then far from shy.
My Argentea was a killer as well. He was all business and would even tolerate a gravel vac in his space. He was one of the meanest fish I've dealt with.
Very nice, natural looking tank man. Snake looks excellent as well.