DD,
Just as Bob Waldrop stated most threadfin loss in small ponds is due to winter predation not temps. I don't think my water temps have ever been below 45 degrees the last several years and rarely even below 50 degrees.
My failures are due to LMB and HSB predation. In winter, every threadfin heads to the deepest water...if that water isn't extensive, the LMB and HSB can literally surround them and eat every single one of the threadfins...which is what happened to me twice. I was a slow learner.
