YP certainly are bottom oriented fish. It seems my perch are always low in the water column. Some dart to the surface to grab pellets, but immediately whirl and dive.
The sunfish in my pond spend time throughout the water column, hovering or suspending at any depth.
Why your newly release fish stayed on the bottom so long could be attributed to stress from being transported. Alternately, your pond's water quality could be radically different from the water they'd been living in.
I've seen newly released YP rest on the bottom for an hour or so, then flick their tails and scoot away when touched with a stick. Can you describe how long the fish were in transportation, what the water temps were, if they were in well oxygenated water, etc.? My hunch is that they will be fine, but I'm no expert.
I did transport a dozen tiger trout last week in not nearly enough water. The trip took an hour. I stopped twice along the way, the first time adding snow to the limited bucket and cooler volume; the second time to borrow several totes from a friend and filling them with river water. All the trout made it and are swimming in our pond today. Several were belly up at my first stop. They'd all recovered by the time I reached my friend's home.
