Not sure I understand the question. You haven't pressed C on the SDS or it would be editable and isn't in your screenshots. That would be what you wanted to do next when your low poly base mesh doesn't permit any more refinement of the shape, and you didn't want to manually insert extra loops but merely wanted to apply the existing subdivision. Still not sure what you are asking though...
Perhaps you are confused about isoline editing ? If that is turned on in view settings, and display mode is also set to isoparms then you should be able to directly edit points on the subdivided mesh result, and the outer low poly cage should be hidden. Is that what you want to happen ?
Here is a similar fish under isoline editing in poly mode - is that what you want yours to look like ?
CBR