Unity Source code for project
Seascape scene: Tile based approach
Seascape2 scene: Terrain based approach
To change the number of fish generated, click on the empty GameObject (either TerrainGen or OceanFloor) and modify the fish number under the "GenerateFish" script.
Note: The rocks I used in the project were of a very high quality and thus increased the project to a size of approximately 200 MB, therefore in the submission they have been replaced with spheres.
The package containing the the original rocks used is available at: https://www.dropbox.com/s/r6gc34mt9jocecu/Seascape.unitypackage