Lovely concept. A monstrous fish emerging from the ocean at night to clearly stalk you, yet the story and colors compliment the fear/shock with a touch of playfulness. Composition reminds me of a classic movie poster, such as from the 1960's.
The textures in this piece are really nice- they add a lot to the overall mood.
If I had to give any critique, it would be that the piece feels a tiny little bit too heavy. The white / magenta section is really empty, and weights the piece towards the upper half. It definitely does a marvelous job in drawing attention to the viperfish, but it's a little bit too simplified compared to everything else. Maybe you could add some subtle texturing?