Looks cool, Ominousplay!

Suggestions for rocks -- in the surface replicator, be sure that you allow for randomization of rotation among the replications.  I've used 180 degrees in all three axes with some success.  I also allow for sizable variation in scale.  One last thing, and I don't remember exactly what it's called in the surface replicator, but you can allow for a certain amount of clumpiness or "tend to stick together" of the replicated objects.  This tends to feel more random than the even distribution that the replictor creates by default.

That said, your scene is coming together really well.  You might put a fog object in the scene to give a feeling of hazy water that the fish are swimming through, or even use the "distant fog" scene atmosphere setting.  Just a thought.  The depth of field is really good in this.

 - Dex