The blenny in this photo is absolutely astonishing and that it's pose and colors greatly contrast the algae-covered home it occupies. Not only does the lighting and depth makes you see such a small fish up close, it's behaving as though it is curious about what it going on outside.
Furthermore, markings on the blenny's dark blue eyes severely complement the pale body it has, and the background is a large one that just makes you want to jump into the water and greet the fish happily.
Finally, as to wrap this critique up, this photo, along with it's colors, pose, and lighting, deserves a 5 out of 5. Excellent job.