On fish where most of the color is metallic spangling the black will make the fish darken up,making the spangling stand out,making them look alot better.
Many(not all) fish with lighter colors(not spangling) like yellows and orange will darken up to brown on a black substrate,making them look worse.
Many(not all) fish with lighter colors(not spangling) like yellows and orange will darken up to brown on a black substrate,making them look worse.