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Anesthesia, Analgesia, and Surgery in Pet Fish

Greg Lewbart M.S., V.M.D., Dipl. ACZM


With the increasing interest in ornamental fish medicine, exotic animal practitioners will find it necessary to provide both anesthesia and analgesia to for their patients. While a number of compounds have been used to anesthetize fish, tricaine methanesulfonate (MS-222) and eugenol (clove oil) will be discussed here. Butorphanol will be reviewed for its analgesic potential.


This sodium channel blocker is the only anesthetic approved for use in food fish. It has a wide margin of safety in a number of species and is the anesthetic of choice at the NCSU-CVM. (1,2)

A buffered stock solution can be made by dissolving one gram of MS-222 and one gram of sodium bicarbonate in 100 milliliters (mls) of distilled water. This solution will contain 10 mg/ml of MS-222 and should be labeled appropriately. The stock solution should be protected from light and adequately labeled with the concentration, date of preparation, and name of person who mixed the solution.


A practical alternative to MS-222 is clove oil (eugenol) that is available at many pharmacies. (3,4) Concentrations of between 25 and 50 mg/L are effective in freshwater and marine species and results are comparable to MS-222, except that recovery may be prolonged. (5)

Eugenol is not completely soluble in water and should be diluted 1:10 in 95% ethanol to yield a working stock solution of 100 mg/ml, since each ml of clove oil contains approximately 1 gram (1000 mg) of drug.

Summary of MS-222 and Clove oil

"Anesthesia induced with Tricaine methanesulfonate or eugenol contributes to hypoxemia, hypercapnia, respiratory acidosis, and hyperglycemia in red pacu (Piaractus brachypomus). Similar to Tricaine methanesulfonate, eugenol appears to be an effective immobilization compound, but eugenol is characterized by more rapid induction, prolonged recovery, and a narrow margin of safety. Care must be taken when using high concentrations of eugenol (over 100 mg/L) for induction, because ventilatory failure may occur rapidly. In addition, analgesic properties of eugenol are unknown." Am J Vet Res 2001;62:337-342.


Preliminary results indicate that koi (Cyprinus carpio) given intramuscular butorphanol at a dose of 0.4 mg/kg IM or SQ prior to recovery from anesthesia return to normal swimming and begin eating sooner than those fish receiving a saline placebo.(6)

FADS (Fish Anesthesia Delivery System)

Details on the FADS and its components can be found in Exotic DVM 1(2), 1999. (7) Once the components of the FADS have been obtained, assembly can begin. A submersible aquarium pump (power head) serves as the water delivery system. Cut five to ten centimeter pieces of each diameter of transparent tubing and telescope them together to form a twenty to forty centimeter piece of anesthesia hose. The final diameter tube should be the longest and appropriate for the size of the patient's buccal cavity. The base portion of the composite tube can be clamped to the power head outflow with a plastic (desirable) or metal clamp. Most commercial power heads are equipped with a venturi tube for aquarium aeration. Because stepping down the anesthesia hose diameter increases backpressure, the venturi tube can act as an irrigator for the anesthetized fish patient. In most cases a ten-gallon aquarium or similar sized plastic container will be of adequate size to serve as the reservoir and support for the FADS. Once the aquarium has been rinsed and cleaned with hot water, and the tube connected to the pump, the pump should be secured to the inside of the aquarium near the bottom of the tank. Most power heads come with suction cup attachment fittings for this purpose. At this point the custom-made Plexiglas support is placed atop the aquarium and should fit securely on the ledge of the plastic rim. Note that there should be at least five centimeters on either side of the Plexiglas support for unobstructed water return to the aquarium. Supplemental aeration can be supplied with a freestanding air pump and air stone. Now the pre-soaked foam surgical platform can be placed atop the Plexiglas support and the anesthesia delivery tube secured to the foam. This can be accomplished with clamps or by cutting a slit in the foam and sliding the tube through it. Plug in the pump and the FADS is ready for operation. Note that with most power head pumps, flow rates are adjustable.


1  Harms CA: Anesthesia in fish. In Fowler ME and Miller RE: Zoo & Wild Animal Medicine Current Therapy 4. Philadelphia: W.B. Saunders Company, pp. 158-163, 1998.

2  Stoskopf MK. Anesthesia of pet fishes. In: Bonagura JD, Kirk RW, eds. Current veterinary therapy XII, small animal practice. Philadelphia: WB Saunders Co, 1365-1369, 1995.

3  Soto CG and Burhanuddin CG: Clove oil as a fish anesthetic for measuring length and weight or rabbitfish (Siganus lineatus). Aquaculture, 136:149-152, 1995.

4  Hikasa Y, Takase K, Ogawawara T, et al. Anesthesia and recovery with Tricaine methanesulfonate, eugenol, and thiopental sodium in the carp, Cyprinus carpio. Japanese Journal of Veterinary Science, 48:341-351, 1986.

5  Sladky KK, Swanson C, Stoskopf MK, Loomis M, and GA Lewbart. Comparative efficacy of tricaine methanesulfonate and clove oil for use as anesthetics in red pacu (Piaractus brachypomus). American Journal of Veterinary Research, 62(3):337-342.

6  Harms CA and GA Lewbart personal observation.

7  Lewbart GA and CA Harms. Building a fish anesthesia delivery system. Exotic DVM Magazine, 1(2):25-28, 1999.

Surgical techniques in the fish patient


Ornamental fish can make excellent subjects for surgery. A large percentage of these patients are nishikigoi (Cyprinus carpio), which are taxonomically an ornamental carp. In the United States and in other parts of the world, nishikigoi are simply referred to as koi. Koi have been selectively bred in Asia for hundreds of years with qualities such as color, pattern, size, and confirmation of utmost importance in terms of desirability and value. It is not uncommon for a koi owner to have between $1,000.00 and $25,000.00 worth of fish in a pond, and this does not include the value of the pond and filtration equipment.

A number of references review the details of fish surgery. (1,2,3,4,5,6,7,8,9,10,11)

Most small and exotic animal hospitals will already possess the necessary surgical instruments and other supplies necessary to perform surgery on fish. A delicate or ophthalmologic pack is helpful when working with small patients. Table 1 contains a list of pertinent materials and supplies.

The skin should be kept moist throughout the surgical. During prolonged procedures, a red rubber catheter and large syringe can be used to carefully moisten the koi patient without splashing water into the incision site. Patient monitoring can be performed with a pulse Doppler or ECG leads (one at the base of each pectoral fin and a third at the base of the anal fin).

A clear plastic avian-style drape has many advantages for fish surgery. The plastic helps retain moisture around the fish, does not allow moisture to leak through and compromise the surgical field, and provides a working surface which stray suture can contact without contamination. A rim of petroleum jelly can be used to adhere the drape to the fish if desired.

Surgical preparation should minimize disruption of the skin and mucus, as these are major barriers to infection. A simple swipe along the intended incision site with a cotton swab soaked in sterile saline, or at most dilute betadine or chlorhexidine solution, to reduce gross contamination suffices in place of a traditional surgical scrub. Removing scales along the incision line facilitates a smooth entry.

Retractors are a valuable tool for visualizing and accessing various internal organs in the koi.

Bipolar cautery works well for hemostasis during koi abdominal surgery.

Needles with a cutting tip facilitate skin penetration. Simple continuous, simple interrupted and continuous Ford interlocking patterns have all been used for skin closure with satisfactory results. Single or two-layer closure can be used depending on the thickness of the body wall. We do not advocate use of cyanoacrylate tissue adhesive, either alone or in combination with sutures. Studies have shown that surgical adhesives can contribute to dehiscence, delay healing, and cause local irritation.(7,12) Skin sutures should be removed in 10-14 days.

Many suture types have been used successfully in fish. Synthetic absorbable sutures may not be readily absorbed in fish. We generally recommend using monofilament suture in the skin to decrease the risk of wicking bacteria into the wound. Other factors in suture selection are tissue reactivity and healing time. Preliminary results from a study in koi indicate that monofilament materials like nylon and polyglyconate (Maxon) are slightly superior to braided suture.(11)


1.  Harms CA and GA Lewbart. Surgery in fish. In: Veterinary Clinics of North America: Exotic Animal Practice (R.A. Bennett ed.), Saunders Co., 2000, 759-774.

2.  Greenwell MG, Vainisi SJ: Surgical management of lipid keratopathy in green moray eels (Gymnothorax funebris). In Proceedings of the International Association of Aquatic Animal Medicine, 1994, pp 179-181

3.  Lewbart GA, Stone EA, Love NE: Pneumocystectomy in a Midas cichlid. J Am Vet Med Assoc 207:319-321, 1995

4.  Summerfelt RC, Smith LS: Anesthesia, surgery, and related techniques. In Schreck CB, Moyle PB (eds): Methods for Fish Biology. Bethesda, Maryland, American Fisheries Society, 1990, pp 213-272

5.  Nadelstein B, Bakal R, Lewbart GA: Orbital exenteration and placement of a prosthesis in fish. J Am Vet Med Assoc 211:603-606, 1997

6.  Probasco D, Noga EJ, Marcellin D, et al: Dermal fibrosarcoma in a goldfish; case report. J Small Exotic Anim Med 2:173-175, 1994

7.  Stoskopf MK: Surgery. In Stoskopf, MK (ed): Fish Medicine. Philadelphia, WB Saunders, 1993, pp 91-97

8.  Harms, C.A., R. S. Bakal, L. H. Khoo, K.A. Spaulding, and G.A. Lewbart. 1995. Microsurgical excision of an abdominal mass in a gourami. JAVMA, 207(9): 1215-1217.

9.  Lewbart GA, Spodnick G, Barlow N et al: Surgical removal of an undifferentiated abdominal sarcoma from a koi carp (Cyprinus carpio). Vet Record 143:556-558, 1998

10. Lewbart GA: Self-Assessment Color Review of Ornamental Fish. Ames, Iowa State University Press, 1998

11. Hurty C, Brazik D, Law JM, Sakimoto, K and G Lewbart: Histologic evaluation of the tissue reaction to five suture materials in the body wall of koi (Cyprinus carpio). Proceedings of the American Association of Zoo Veterinarians and the International Association for Aquatic Animal Medicine, 2000, p. 510.

12. Petering RW and DL Johnson: Suitability of a cyanoacrylate adhesive to close incisions in black crappies used in telemetry studies. Trans Am Fisheries Soc 120:535-537, 1991.

Table 1. Surgical Supplies and Equipment

Surgery pack

Suture absorbable and non-absorbable (monofilament)

Cotton-tipped swabs

Clear plastic drape

Sterile saline

Surgery sponges (2x2 or 4x4)

Scalpel blades

Surgical gloves (selection of sizes)



Scrub Tops

Head loupes

Gelpi retractors

+/-Doppler flow probe

+/- ECG


Antibiotics (injectable)

Butorphanol (at 0.1-0.4 mg/kg IM/SQ)

Triple antibiotic ointment

Povidone iodine ointment


Salt (1 - 3 ppt in recovery tank)

** These notes have been modified from the 2001 International Conference on Exotics (ICE) Proceedings with permission.

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