EVALUATION OF IMMERSION IN EMULSIFIED ISOFLURANE OR PROPOFOL AS PART OF A TWO-STEP EUTHANASIA PROTOCOL IN MARBLED CRAYFISH (PROCAMBARUS VIRGINALIS)

The marbled crayfish (Procambarus virginalis) is a parthenogenetic invasive species across much of the world, and when found, euthanasia is often recommended to reduce spread to naïve ecosystems. Euthanasia recommendations in crustaceans includes a two-step method: first to produce nonresponsiveness and then to destroy central nervous tissue. Minimal data exist on adequate anesthetic or immobilization methods for crayfish. A population of 90 marbled crayfish was scheduled for euthanasia due to invasive species concerns. The population was divided into six treatment groups to evaluate whether immersion in emulsified isoflurane or propofol solutions could produce nonresponsiveness. Each group was exposed to one of six treatments for 1 h: isoflurane emulsified at 0.1%, 0.5%, 2%, 5%, and 15% or propofol at 10 mg/L and then increased to 100 mg/L. Crayfish from all treatment groups were moved to nonmedicated water after completion of 1 h and observed for an additional 4 h. All crayfish treated with isoflurane showed lack of a righting reflex at 5 min and loss of movement after 30 min. By 240 min (4 h), none of the crayfish from the isoflurane treatment groups regained movement. None of the crayfish in the propofol treatment achieved loss of reflexes or responsiveness, and all remained normal upon return to nonmedicated water. Isoflurane emulsified in water produces nonresponsiveness that is appropriate for the first step of euthanasia, while propofol was insufficient at these treatment doses.

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.

Bupivacaine as a euthanasia agent for African Clawed Frogs (Xenopus laevis)

Immersion in tricaine methanesulfonate (i.e. TMS) has been used for euthanasia of Xenopus laevis (African Clawed frogs). However, the time for preparation and potential human health hazards may pose as a barrier for large group culls. Here, we aimed to investigate whether immersion in bupivacaine is an effective means to euthanize this species. In experiment one, frogs (n = 10/group) were randomly assigned to 1-h immersion in 1 of 3 treatment groups: 1) TMS-5 (MS-222, 5g/L); 2) TMS-10 (MS-222, 10 g/L); or 3) Bupi-1.5 (0.5% Bupivacaine, 1.5 g/L). Frogs were then removed from solutions, rinsed with system water, and placed into a recovery cage. Heart rate was evaluated audibly via doppler ultrasound flow over 1 min at immediate removal (T1h), at 2 (T2h), and 3 (T3h) h in the recovery cage. In experiment two, frogs (n = 7/group) underwent 5-h & 19-h immersion in either TMS-5 or Bupi-1.5, with heart rate assessment at 5 and 19 hrs. Righting reflex and withdrawal reflex of the hindlimb were tested during the experiments. Experiment one-after the 1-h immersion, Bupi-1.5 treated animals had decreased heart rates compared to TMS-5 and TMS-10 treated animals by T2h. Neither TMS-5, TMS-10, nor Bupi-1.5 ceased heart rate after the 1-h immersion. Experiment two-after the 5-h immersion, Bupi-1.5 and TMS-5 treated animals were comparable in heart rates. 43% of TMS-5 animals and 14% of the Bupi-1.5 animals had completely ceased heart rates at T5h. At 19 h all remaining animals exhibited rigor mortis and had ceased heart rate. We recommend 19-h of immersion using either TMS-5 or Bupi-1.5 for cessation of heart rate in African Clawed frogs. These data are strong support for the use of secondary physical methods for euthanasia in African Clawed frogs when euthanasia by immersion is performed.

Euthanasia Complications in Non-Domestic Species

There are very few studies describing euthanasia complications in non-domestic species. The goal of this study was to survey veterinarians to determine what complications may commonly occur during the euthanasia of non-domestic species. An online survey was sent to seven professional organization listservs containing veterinarians most likely to practice on non-domestic species. Forty-one cases of euthanasia complications were reported. The most common taxa reported were mammals, (23/41, 56%), followed by avian (8/41, 20%), reptile (7/41, 17%), and fish (3/41, 7%). Most animals were reported to have been anesthetized prior to euthanasia (28/41, 68%). The most common method of euthanasia was pentobarbital (27/41, 66%). The reported euthanasia complications included “took an excessive amount of euthanasia solution” (12/41, 29%), “heart would not stop” (9/41, 22%), “animal awoke at a later time” (4/41, 10%), “a secondary method of euthanasia was required” (4/41, 10%), and “other” (12/41, 29%). This study reports complications that can occur during the euthanasia of non-domestic species. The concept of dysthanasia, a euthanasia with an undesirable outcome, has not been previously discussed in the context of zoo, wildlife, aquarium, and exotic pet practice. Strategies to reduce dysthanasia from both animal and human perspectives are explored, including alternative euthanasia techniques, principal-based euthanasia, and mental health implications.

COMPARISON OF THREE CONCENTRATIONS OF AQUA-SEDTM FOR IMMERSION EUTHANASIA OF BUTTERFLY SPLITFIN (AMECA SPLENDENS)

The efficacies of three concentrations of 2-phenoxyethanol from Aqua-sed^TM were examined to determine the suitability for euthanasia of butterfly splitfin (Ameca splendens). Thirty fish were randomly assigned to be immersed in one of three Aqua-Sed^TM concentrations: 0.5, 2, and 6 ml/L. Opercular rates and caudal fin stroke rates were quantified, and time to the cessation of physiological measures including heartbeat, caudal fin strokes, reaction to external stimuli, righting reflex, swimming, and operculation were recorded. To test for the effects of concentration of Aqua-sed^TM on all times to cessation of physiological measures, a linear mixed model was performed followed by pairwise comparisons with a Bonferroni correction. A proportions test compared the number of fish that lost their heartbeat across Aqua-sed^TM concentrations. Varying anesthetic induction times were observed for all three Aqua-sed^TM concentrations; time to cessation of physiological measures was fastest with 6 ml/L, followed by 2 then 0.5 ml/L, but only concentrations of 2 and 6 ml/L induced anesthesia in less than the recommended 180 s. Aqua-sed^TM concentration had a significant effect on time to cessation of physiological measures (P < 0.01), but not on time to cessation of a heartbeat (P > 0.05). Pairwise comparisons indicate time to cessation of caudal fin strokes, reaction to external stimuli, righting reflex, and swimming significantly decreased as concentration increased (P < 0.01). After 60 min of immersion in Aqua-sed^TM the number of fish without a heartbeat differed significantly across concentrations (P < 0.01); 20% of fish immersed in 0.5 ml/L, 90% of fish immersed in 2 ml/L, and 90% of fish immersed in 6 ml/L had no heartbeat. A minimum dose of 2 ml/L of Aqua-sed^TM, and an immersion time of 60 min for euthanasia of butterfly splitfin is recommended, with a secondary euthanasia measure to confirm death when the heartbeat remains.

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.

Fish Sedation and Anesthesia

Veterinarians often need to sedate or anesthetize fish to perform physical examinations or other diagnostic procedures. Sedation may also be required to transport fish. Painful procedures require complete anesthesia with appropriate antinociceptive agents. Regulations and withdrawal times apply to food animal species in many countries. Specific protocols are therefore warranted in commercial fish versus ornamentals. Tonic immobility of elasmobranchs and electric anesthesia should never be used to perform painful procedures. Anesthetic monitoring in fish remains challenging. This review summarizes ornamental fish anesthesia and discusses techniques used in the commercial fish industry and in field conditions.

USE OF TRICAINE METHANESULFONATE, CLOVE OIL AND 2-PHENOXYETHANOL FOR IMMERSION EUTHANASIA OF UNGA CICHLIDS (SAROTHERODON LINELLII)

Fish may warrant euthanasia for a variety of reasons, but euthanasia may be difficult to accomplish or confirm because fish can recover from deep anesthesia even after cardiac and respiratory arrest. The efficacies of three types of anesthetics were evaluated to compare their suitability for euthanasia of Unga cichlids (Sarotherodon linellii). Thirty cichlids were randomly assigned to be immersed in one of the three anesthetic solutions: tricaine methanesulfonate (MS-222), 2-phenoxyethanol (2-PE), and clove oil (CO) at doses of 1,000 mg/L, 2 mL/L, and 500 mg/L respectively. The opercular rates and caudal fin stroke rates were quantified, and the time to cessation of physiological measures (CPM) including caudal fin strokes, the reaction to external stimuli, the righting reflex, swimming, and operculation were recorded. Varying anesthetic induction times were observed with all three euthanasia solutions; the time to CPM in the 2-PE group occurred at a significantly slower rate than in the MS-222 group (P < 0.01). No significant differences were identified for the time to CPM when comparing the standard length or weight of the cichlids in all euthanasia solutions (P > 0.05). The cost of euthanasia per cichlid was calculated, with the most economically viable option being 2-PE; at more than seven times the price of 2-PE, MS-222 was the most expensive. After a 60-min immersion in the euthanasia solution, the presence of an audible heartbeat was identified in 100% of the cichlids immersed in 2-PE, 100% immersed in CO, and 90% in MS-222, indicating that they were not reliably euthanized. Therefore, a two-step protocol is recommended in cichlids for euthanasia: heavy anesthesia via immersion followed by an intravenous or intracardiac injection of euthanasia solution, or other secondary method of euthanasia.

Preliminary Investigations into Use of Metomidate for Euthanasia of Ornamental Fishes

The goals of this study were to investigate the potential use of metomidate for one-step euthanasia of ornamental fish species representing commonly sold families in the ornamental fish trade and to determine a baseline euthanasia dose for most species tested. Metomidate hydrochloride, a rapid-acting, water-soluble, nonbarbiturate hypnotic related to etomidate, was tested at various concentrations and durations for euthanasia of species representing the following freshwater and marine aquarium fish families: Apogonidae, Ariidae, Blenniidae, Callichthyidae, Characidae, Cichlidae, Cyprinidae, Gobiidae, Gyrinocheilidae, Loricariidae, Melanotaeniidae, Osphronemidae, Pimelodidae, Poeciliidae, Pomacentridae, and Pseudochromidae. Fish in each trial were euthanized as a group (n = 1). Most groups contained 10-12 fish. Some higher doses required buffering. Euthanasia was considered successful if all fish in each group did not recover after 6 h in unmedicated water. All species immediately lost buoyancy and equilibrium, dropping to the tank bottom within 1 min and ceasing ventilation typically within minutes. However, reactivity to vibration, sound, or touch was noticeable for varying time periods afterward (8-66 min), so an additional 30 min of exposure after cessation of reactivity was included as part of the protocol. Although some species (Neon Tetras Paracheirodon innesi and Australian Rainbowfish Melanotaenia australis) were euthanized at a concentration of 40 mg/L metomidate for a total exposure time of 38 min, most species tested were successfully euthanized with metomidate at a concentration of 100 mg/L, with total exposure times ranging from 35-96 min. A few catfish species (Otocinclus sp. and Bronze Corydoras Corydoras aeneus) were refractory and recovered after 100 mg/L. However, Otocinclus sp. were successfully euthanized at 250 mg/L, and Bronze Corydoras were euthanized at 1,000 mg/L. Further studies are needed to provide additional data for these and other species and families, for different water chemistry conditions, and for various biological factors to fine-tune dosing regimens.

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

Immersion in tricaine methanesulfonate (MS-222) is insufficient for euthanasia in at least one species of fish. The current study investigated the effectiveness of potassium chloride (KCl) to euthanize anesthetized koi (Cyprinus carpio). Twenty-eight healthy koi were anesthetized via immersion in 500 mg/L of buffered MS-222 for 10-12 min, manually removed to room air, and randomly administered 10 mEq/kg KCl (333 mg/ml) via one of three routes-intracardiac injection (IC) (n = 7), intracoelomic injection (ICe) (n = 7), or topical instillment over the gill filaments bilaterally (T) (n = 7)-or received no treatment (control, C) (n = 7). A Doppler ultrasonic flow detector was placed over the heart, and sounds were assessed continuously from immediately prior to treatment until 5 min posttreatment and every 5 min thereafter until Doppler sound cessation, resumption of operculation, or 30 min. Time to Doppler sound cessation or resumption of operculation was recorded. Doppler sound cessation occurred in 7/7 fish in IC (median 0.08, range 0-2.75 min) and 1/7 fish in T (10 min). In T, ICe, and C, 6/7, 7/7, and 7/7 fish, respectively, maintained Doppler sounds to 30 min. All fish in ICe (7/7) and C (7/7) resumed operculation with median (range) times of 22 (7-30) min and 16 (9-29) min from treatment, respectively. Intracardiac KCl at 10 mEq/kg rapidly ceases Doppler sounds and is a successful technique for euthanasia of anesthetized koi. Intracoelomic and topical KCl at 10 mEq/kg were not effective for euthanasia of koi.

THE EFFECT OF ANESTHETIC TIME AND CONCENTRATION ON BLOOD GASES, ACID-BASE STATUS, AND ELECTROLYTES IN KOI (CYPRINUS CARPIO) ANESTHETIZED WITH BUFFERED TRICAINE METHANESULFONATE (MS-222)

Anesthesia is commonly employed in aquatic medicine to facilitate physical exams, diagnostics, and surgical interventions. Tricaine methanesulfonate (MS-222) is the most commonly used anesthetic for fish and is currently the only anesthetic approved by the US Food and Drug Administration Center for Veterinary Medicine for food-producing fish. Despite the frequency of anesthetic procedures in fish, anesthetic monitoring remains rudimentary in many facilities. This study evaluated the impact on blood gases, acid-base balance, and electrolytes in koi (Cyprinus carpio) anesthetized at concentrations of 100 mg/L and 150 mg/L MS-222. Blood samples from 25 fish per treatment were collected at 5 and 20 min of anesthetic immersion. Forty-nine of 50 fish recovered uneventfully from anesthesia; one fish did not recover and was euthanatized. Results showed significant increases in partial pressure of carbon dioxide (pCO₂) (P = 0.006) and hyperglycemia (P = <0.0001) with increasing anesthetic concentration and time under anesthesia and a significant decrease in partial pressure of oxygen (pO₂) with increased anesthetic time (P = 0.021). There were several electrolyte changes observed with both increasing anesthetic time and concentration. All electrolytes except potassium remained within published reference ranges for koi, while potassium showed a significant decrease in concentration associated with anesthetic time and concentration. The results of this study indicate that MS-222 at 100 mg/L and 150 mg/L represent safe anesthetic concentrations for koi undergoing minimally invasive diagnostics; however, koi anesthetized with MS-222 at a concentration of 150 mg/L experienced more significant changes in blood gases, acid-base balance, and electrolyte concentrations.