Mmmm, love the blue-spotted stingrays. I've always wanted to try one of those in my tank. They tend to be pretty picky eaters though, so I've always shyed away. Haven't seen any come through the trade lately though. Most of what I see are common pacific rays.
The penguin shot shows their natural camoflauge really well, but in order for it to be a more standout photo, I'd shoot it with a much longer lens to try and get the DOF shorter (blur the background more and make the little penguin stick out).