Also, some species of trout are better than others in ponds where O2 and water temp may be marginal - that should be considered. Dr. Mark Cornwell has written several articles on trout ponds in PBMag (in his "On Northern Pond" column) which would be valuable info for you.
In your situation when the Secchi disk is 8ft to 10ft your trout will survive year round. You need the water clarity for dissolved oxygen (DO) production below the thermocline in the cold water basin.
We (I) always think about water temps when we're discussing trout in ponds. This is the first I can remember the importance of clear water for plant life below the thermocline being pointed out. Thanks, Bill! (Of course, it may have come up many times that I forgot.)