What is "deep-skinned tilapia"?
Your post got my curiosity up.
I think it is referring to the degree (depth) of skin removal rather than referring to a specific variety of talapia.
The images in the site listed below cause me to think that "thick skinned" means the fish is skinned more vigorously (cut deeper) as opposed to the image of the "shallow skinned" which has more color left from the skin. Probably not explaining well, but the photo's will make it clearer.