Fish are a great idea! As for DOF, just because a technique is possible doesn't mean you SHOULD use it... And in this case I think that DOF blurring would change the scale, and make the scene more microspic-feeling. The only thing one would have then to "set the scene scale" would be the beach ball, but diferent people perhaps have different ideas of how big beachballs should be. One person might see it as a fishing bobber floting awry...? Lovely fish!