Catfish food should be easy to find. Gamefish Chow 32% is another alternative.
Here is some more info on CC from SRAC. Blues have slightly higher protein requirements as per Bill's cite.
Commercial feeds for food fish generally contain 28% or 32% protein. A 26% protein feed is also available from some feed mills. Research has shown that protein levels as low as 24% can support maximum growth if fish are fed as much as they will eat. Low-protein feeds cost less, but usually result in more body fat and lower processed yield. Research has shown that there is a marginal difference in the processed yields of fish fed a 28% or 32% protein feed (about 0.3 to 0.4 percentage unit reduction in fish fed the 28% protein diet), but the difference may be significant to catfish processors. The type of feed to choose depends on whether fish prices are based on live weight or on processed yield. Although fish fed higher protein feeds (35% to 40%) have better processed yield and lower body fat content, these feeds usually are not economical.