Please remind me -- can I stock these in a mature BG/LMB pond with any hope of recruitment?
Yes, I recommend some emergent/submergent vegetation present in order for GS to escape predation. However, even in some of my ponds without vegetation the GS persisted - they moved very shallow and foraged and hid in FA in very shallow water [6" depth].
Many men go fishing all of their lives without knowing that it is not fish they are after. ~ Henry David Thoreau