In zoological medicine, understanding pain and analgesia is limited by our ability to define and measure pain, as well as our limited knowledge of analgesic drug efficacy and mechanisms of action. While few studies are available on fish pain and analgesia,1,2,5,6 controversy exists regarding the ability of fish to experience pain.3,4 Our objectives were to: 1) develop and validate an ethogram in koi (Cyprinus carpio), specifically to quantify nociceptive and antinociceptive behavior before and after unilateral gonadectomy; and 2) evaluate the safety, efficacy, and side effects of the opioid analgesics, butorphanol and morphine for post-surgical pain in koi. Adult koi (n=90) received either physiologic saline (0.09%), butorphanol tartrate (10 mg/kg), or morphine sulfate (5 mg/kg) in three treatment categories: drug only (n=6 for each drug), drug with anesthesia and surgery (n=12 for each drug), and drug with anesthesia, but without surgery (n=12 for each drug). Physiologic and behavioral data were recorded pre- and post-treatment. In addition, a blood sample was collected (0.1 ml) before anesthesia and after surgery to assess PCO2 (mm Hg), PO2 (mm Hg), pH, and lactate (mmol/L).
Of the koi undergoing surgery, those receiving only saline showed a marked decrease in interactive behavior, food consumption, and activity, which lasted for greater than 72 hr. In contrast, for those koi receiving either morphine or butorphanol, food consumption and interactive behavior had returned baseline values within 3 hr post-surgery. Activity for both butorphanol and morphine surgery groups significantly decreased from baseline following surgery and returned to normal within approximately 48 hr post-surgery. Though statistically insignificant, post-surgical blood values increased for lactate and PO2 and decreased for pH and PCO2. In summary, koi undergoing unilateral gonadectomy without analgesics do not exhibit normal behavior, while both morphine and butorphanol appear to produce antinociception. Butorphanol administration was associated with the most significant respiratory depression compared to morphine or saline. In addition, most koi receiving butorphanol, regardless of surgery or sham, showed temporary, abnormal buoyancy characterized by the tail near the water surface and head directed toward the tank bottom. Thus, morphine appears to be the most appropriate choice for analgesia in koi.
Supported by a grant from the Morris Animal Foundation, Englewood, CO, 80112 USA.
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