Pain and analgesia are poorly understood in reptiles, which are commonly maintained in zoological institutions and as laboratory and companion animals. Thus, we developed a behavioral ethogram to evaluate pre-operative and post-operative responses to a thermal stimulus, feeding, movement, and breathing in red-eared slider turtles (Trachemys scripta elegans). We hypothesized that opioid drug administration would allow for a more rapid return to pre-operative behavior following a unilateral orchidectomy. The antinociceptive efficacy of morphine (2 mg/kg SC; mu-opioid receptor agonist) and butorphanol (20 mg/kg SC; mixed kappa-opioid receptor agonist and mu-opioid receptor antagonist) were evaluated because of their extensive use as analgesics in veterinary medicine. Compared to sham-saline turtles, surgery-saline turtles exhibited severely depressed feeding and increased movement at 2–8 h postoperation. Butorphanol did not alter feeding, movement, or breathing compared to saline in both sham- and surgery-treated turtles. Morphine depressed feeding and breathing for 1–2 days postoperation, but did not alter movement compared to saline except during the 2–8 h post-operation period. Our results show that pain in red-eared slider turtles is manifested as decreased feeding and increased spontaneous movement. Although turtles returned to normal behavior by 2 days following unilateral orchidectomy, a mu-opioid analgesic drug should be administered for at least 48 h following a surgical procedure.