EVALUATION OF POTASSIUM CHLORIDE ADMINISTERED VIA THREE ROUTES FOR EUTHANASIA OF ANESTHETIZED KOI (CYPRINUS CARPIO )

EVALUATION OF PLASMA CORTISOL AND LACTATE IN KOI (CYPRINUS CARPIO) EUTHANIZED BY IMMERSION IN TRICAINE METHANESULFONATE, CLOVE OIL, OR CARBON DIOXIDE GAS DISSOLVED IN WATER

Little research has taken place on the effect of euthanasia methods on biophysical and biochemical changes at the time of euthanasia in fish. These changes are used in multiple species to determine stress levels before death. Koi (Cyprinus carpio) are an important fish species often used in laboratory research, kept in backyard ponds, and managed in zoological and aquarium collections. The current study evaluated euthanasia of koi by immersion in 0.5 g/L tricaine methanesulfonate (MS-222) (n = 10), 0.5 g/L clove oil (n = 8), 1 g/L clove oil (n = 10), and CO2 (n = 7) on time to cessation of opercular movement, plasma lactate levels, and plasma cortisol levels. CO2 had the longest mean time to cessation of opercular movement, and MS-222 had the shortest (mean CO2: 24.9 min, range 13.18-31.35 min; MS-222: 2.68 min, range 1.33-4.5 min). The difference was not significant between any of the groups for plasma cortisol or lactate levels. MS-222 demonstrated the highest cortisol levels, and CO2 had the lowest (mean CO2: 108.7 ng/ml, range 33.9-195.8 ng/ml; MS-222: 650.6 ng/ml, range 77.3-2374.9 ng/ml). Average lactate levels were highest for 1 g/L clove oil and lowest for 0.5 g/L clove oil (mean 0.5 g/L clove oil: 5.1 mmol/L, range 1.8-8.1 mmol/L; 1 g/L clove oil: 7.4 mmol/L, range 5.6-10.5 mmol/L).

POTASSIUM CHLORIDE ADMINISTERED VIA FOUR ROUTES FOR EUTHANASIA OF ANESTHETIZED GOLDFISH (CARASSIUS AURATUS)

Immersion overdose in tricaine methanesulfonate (MS-222) is ineffective for euthanasia of adult goldfish (Carassius auratus), and investigation of alternative techniques is warranted. This study evaluated potassium chloride (KCl) administered via four routes for goldfish euthanasia. Thirty clinically healthy adult goldfish (17.2-41.9 g) were anesthetized via immersion in buffered MS-222 (300 mg/L) for 5 min beyond anesthetic induction. Fish were then randomly administered one of five treatments: KCl (333 mg/mL, 4.5 mmol/mL, 4.5 mEq/mL) via intracardiac injection at 10 mEq/kg (IC), intracoelomic injection (ICe) or bilateral topical delivery over the gill filaments (T) at 100 mEq/kg, or 90-min immersion at 4,500 mEq/L (saturated solution) dissolved in induction solution (water [W]), or no treatment (control [C]). Following treatment, all fish were moved to anesthetic-free freshwater. Serial heart rates were collected via Doppler device until sound cessation or recovery. Median (range) time to perform treatments was 5.3 (1.2-8.0) min, 3 (3-3) s, and 10 (10-10) s in IC, ICe, and T, respectively. Doppler cessation occurred in 6/6, 6/6, 6/6, 6/6, and 0/6 fish in median (range) times of 3 (0-210), 18 (10-45), 118 (90-390), and 150 (60-240) min in IC, ICe, T, W, and C, respectively; this was significantly different between groups (P = 0.002). Following or during treatment, 1/6, 2/6, 6/6, and 4/6 fish in IC, ICe, T, and W, respectively, exhibited intermittent transient jerking movements. Median (range) time to recovery in C was 5.5 (3.5-6.5) min. All administration routes were effective, but time to Doppler cessation varied and transient movements were noted. Preliminary follow-up research determined that return to MS-222 induction solution following ICe KCl treatment abolished movements. ICe KCl at 100 mEq/kg was technically simple and resulted in Doppler sound cessation in a clinically relevant time frame in 6/6 anesthetized goldfish. Return to MS-222 immersion following KCl administration is recommended.

Evaluation of Targeted Injections of Ivermectin or Potassium Chloride for Euthanasia of Anesthetized Thorny Devil Stick Insects (Eurycantha calcarata)

Insects are commonly utilized in biomedical research and have become increasingly popular in museum collections and as pets. Despite this, objective evaluation of insect euthanasia is scarce. This study investigated the effectiveness of targeted injections of ivermectin or potassium chloride (KCl) for the euthanasia of anesthetized thorny devil stick insects (Eurycantha calcarata). Ten clinically healthy mature insects (six males, four females) were enrolled. Insects were weighed and anesthetized via exposure to a cotton ball soaked with 1.6 mL of liquid isoflurane in a 1 L sealed chamber until loss of righting reflex and response to stimulation (induction). Insects then received one of three treatments: ivermectin 100 mg/kg (n = 4), KCl 200 mEq/kg (n = 4), or 0.9% sodium chloride 100 mL/kg (n = 2) injected along the ventral thoracic midline between the first leg plate and the caudal adjacent plate. Following injection, insects were serially monitored for return of spontaneous movement and righting reflex. Death was defined as the absence of spontaneous movement for 48 h. Median (range) induction time and isoflurane concentration at induction was 36 (22–39) min (n = 9) and 22 (19–22)%, respectively. Euthanasia was successful in 4/4, 3/4, and 0/2 isoflurane-anesthetized insects receiving ivermectin, KCl, or 0.9% sodium chloride, respectively. Recovery was prolonged at 10.5 (sodium chloride female), 11.0 (KCl male), and 18.0 (sodium chloride male) hours. This is the first prospective investigation of euthanasia in adult E. calcarata. In this preliminary study, ivermectin 100 mg/kg via ventral midline injection was effective for euthanasia of thorny devil stick insects.

EVALUATION OF INTRACARDIAC ADMINISTRATION OF POTASSIUM CHLORIDE, IVERMECTIN, OR LIDOCAINE HYDROCHLORIDE FOR EUTHANASIA OF ANESTHETIZED BLUE CRABS (CALLINECTES SAPIDUS)

Methods to anesthetize and euthanize aquatic invertebrates have proven unreliable in decapods; thus studies to optimize euthanasia techniques for crustaceans are needed. Study objectives were to evaluate efficacy of intracardiac potassium chloride (KCl), ivermectin, or lidocaine hydrochloride (HCl) for euthanasia of anesthetized blue crabs (Callinectes sapidus). Twenty adult male crabs (n = 5/group) were immersed in 500 mg/L eugenol for 5 min beyond loss of the righting reflex and then randomly administered intracardiac 10 mEq/kg KCl (333 mg/mL), 5 mg/kg ivermectin (10 mg/ml), 100 mg/kg lidocaine hydrochloride (HCl) (20 mg/ml), or 5 ml/kg saline (0.9%). Serial heart rate assessments were made using a Doppler probe placed over the dorsum, and times to loss of righting reflex, Doppler sound cessation, and/or recovery were recorded. Median (range) time to loss of righting reflex was 32 (17-57) min. One crab in all groups, except lidocaine HCl, had no detectable Doppler sounds prior to injection. In the remaining crabs, Doppler sound cessation occurred in 4/4, 4/4, 4/5, and 0/4 crabs administered KCl, ivermectin, lidocaine HCl, and saline, respectively. Median (range) time to Doppler sound cessation was 30 (0-55), 18 (16-28), and 50 (0-90) s in KCl, ivermectin, and lidocaine HCl groups, respectively. Tonic limb movements were observed in 5/5 KCl-treated crabs. Median (range) time to recovery was 180 (115-345) and 300 m in four saline-treated crabs and one lidocaine HCl-treated crab, respectively. Intracardiac KCl at 10 mEq/kg and ivermectin at 5 mg/kg were effective, rapid methods for euthanasia of anesthetized blue crabs.

Evaluation of prolonged immersion in tricaine methanesulfonate for juvenile goldfish (Carassius auratus) euthanasia

OBJECTIVE

Doses of buffered tricaine methanesulfonate (MS-222) up to 1000 mg/L for 15 minutes are reported inefficient to produce euthanasia in goldfish. The goal of this study was to determine if goldfish can be euthanized by more prolonged immersion in MS-222.

ANIMALS

24 healthy goldfish (weight range: 1 to 10 g) were randomly assigned to 4 groups of 6 fish.

PROCEDURES

The first group (G1) was exposed to 500 mg/L buffered MS-222 for 15 minutes then placed in freshwater for 3 hours. The second (G2) and third groups (G3) were exposed to 1000 mg/L of buffered MS-222 for 15 minutes then placed in freshwater for 3 hours and 18 hours respectively. The fourth group (G4) was exposed to 1000 mg/L of buffered MS-222 for 60 minutes then placed in freshwater for 3 hours. Time to cessation and return of operculation were recorded. If the goldfish did not resume operculation, heart rate was evaluated by Doppler ultrasonic flow detector.

RESULTS

Median times to apnea were 35 seconds at 1000 mg/L and 65 seconds at 500 mg/L. Re-operculation occurred only in G1 in 5 out of 6 individuals. All fish from G1, 3 fish from G2, 0 fish from G3, 1 fish from G4 had remaining heartbeats at the end of the observation period.

CLINICAL RELEVANCE

Overall, a dose of 1000 mg/L of buffered MS-222 for 15 minutes was efficient to euthanize juvenile goldfish at 20 °C. Different fish body mass and water quality parameters might explain different results compared to previous studies.

Use of potassium chloride for low-residue euthanasia of anesthetized California sea lions (Zalophus californianus) and northern elephant seals (Mirounga angustirostris) with life-threatening injury or disease

OBJECTIVE

To demonstrate the efficacy of potassium chloride (KCl) for low-residue euthanasia of anesthetized pinnipeds in field settings for which carcass retrieval for disposal is not feasible.

ANIMALS

Stranded, free-ranging California sea lions (CSLs; Zalophus californianus; n = 17) and northern elephant seals (NESs; Mirounga angustirostris; 6) with life-threatening injury or disease between May and August 2020.

PROCEDURES

Each animal was anesthetized and then received a lethal dose of KCl solution administered by IV or intracardiac injection. The effective KCl dose; durations to cardiac arrest, respiratory arrest, and pupil dilation; and presence or absence of agonal breaths, muscle fasciculations, or skeletal movements were recorded.

RESULTS

Mean effective dose of KCl was 207.4 mg/kg (94.3 mg/lb) for the 17 CSLs and 209.1 mg/kg (95.0 mg/lb) for 5 of 6 NESs (1 outlier NES was excluded). The range in duration from the beginning of KCl injection to cardiac arrest was 0 to 6 minutes, to pupil dilation was 0 to 5 minutes, and to respiratory arrest was 0 to 5 minutes. Muscle fasciculations, skeletal movements, and agonal breaths were observed in both species during and after KCl administration.

CONCLUSIONS AND CLINICAL RELEVANCE

The use of KCl provides an effective, low-residue method of euthanasia in anesthetized CSLs and NESs. Our recommended dose for these species is 250 mg KCl/kg (113.6 mg KCl/lb) delivered by intracardiac injection. Compared with euthanasia by barbiturate overdose, the use of KCl reduces the potential for secondary intoxication of scavengers and is appropriate in field scenarios in which the carcass cannot be retrieved for disposal.