To determine how initial length affects survival of captively-reared juvenile suckers, we introduced Passive Integrated Transponder (PIT) tagged juvenile suckers into three net pens in Upper Klamath Lake. The suckers originated from the U.S. Fish and Wildlife Service's Sucker Assisted Rearing Program in Klamath Falls, Oregon, which rears suckers collected as larvae in Upper Klamath Lake including Lost River sucker (Deltistes luxatus), shortnose sucker (Chasmistes brevirostris), and Klamath largescale sucker (Catostomus synderi). Suckers were monitored continuously by PIT antennas. These data contain all remote detections from the PIT antennas, all physical captures, water quality data associated with each net pen, and dates when damage to two of the net pens was first detected. The results from a diagnostic work-up following standard fish health methods of four moribund suckers that were exhibiting fin hemorrhage and tail erosion during the study are also contained in these data.