As was suggested, depth was added to the volume and the ravine opening was opened up further. The next step will be to add ledges and make the rock more jagged. But so far I believe we are making steps in the right direction. Also ends to the ravine are needed as it would be surrounded by the seabed in the final production.
The sphere represents our fish. As can be seen this ravine is definitely very large, which should give plenty of time for the fish to travel upwards. It was suggested that there could be a sharp turn to encourage the fish to swim up but that proved slightly difficult without tearing the lower sections of the ravine which would make moving the camera more difficult.
To add ease to contruction and animation the ravine has been into three sections that can be switched on and off depending on on what angle we need to look at. One for the left-hand side, one for the right-hand side and one for the floor. It also makes seeing the floor in wireframe view easier. In theory these can all be stitched up for the final model. So there would be a construction layer and a polygon layer with a definable transition. Currently the joins between the rock and the ground appear rather artificial when smoothed out.
The join could certainlydo with some unevenness to it anyway as it currently all joins on the same level which does appear rather unrealistic.