No good reason for a single species (BG) die-off vs LMB. Similar cold tolerance and DO profile.
ewest, I also doubt that all of the BG died. But if the pond was stocked with CNBG and the LMB were all Northern strain, a large population of the BG could have perished.
I'd suggest either running a seine through the pond to assess the fish population, only stock adult BG, or Rotenone it and start fresh.
