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Fish Anesthesia

When working with a new anesthetic protocol or species it is advisable to anesthetize a few fish and follow them through full recovery to insure drug dosages and techniques are safe and provide sufficient anesthetic depth for the intended procedures.

Fish are often fasted for 12-24 hours prior to anesthesia to reduce the risk of regurgitation of food that may lodge in the gills or foul the water. Fasting also decreases fecal contamination of water used for anesthesia and recovery.

Adequate oxygenation is necessary for maintenance of normal physiologic homeostasis during fish anesthesia. Oxygen should be supplied, via an air stone or similar device, to all water chambers used during transport, anesthesia and recovery.

Ideally, water taken from the original fish holding tank can be used in transport, anesthetic and recovery chambers. If water from another source is to be used, water quality parameters (i.e., chlorine, temperature, pH and ammonia) should closely duplicate that of the original holding tank.

Anesthetic agent

MS-222 (tricaine methanesulfonate)

75-125 mg/l (induction) and 50-75 mg/l (maintenance)

Sodium bicarbonate should be added to stock solution to maintain neutral pH.

Only FDA approved anesthetic for fish (21 day withdrawal).

Clove oil

40-100 mg/l (depending on fish species and anesthetic depth)

Active ingredient is eugenol. Clove oil stock solution (100mg/ml) made with 95% ethanol. Stock solution is added to induction chamber at 40-100 mg/l. Not approved for use in fish that may be used for food or released into public waterways.

Benzocaine hydrochloride

25-100 mg/l

Sodium bicarbonate may need to be added to stock solution to maintain neutral pH.

Small margin of safety between effective and lethal doses.


When a fish reaches the level of anesthesia sufficient to perform surgery, there is a total loss of equilibrium and muscle tone, decreased respiratory rate and no response to stimuli. A firm squeeze at the base of the tail may be used to determine response to stimuli.

Respiratory rate may be evaluated by observing movement of the operculum (rigid flap that covers the gills) as it opens and closes. Gill color should be dark pink to light red. If respirations become extremely slow or stop, the fish may be placed in anesthetic-free recovery water until respirations resume.

Water temperature should be maintained at the species normal optimum during both anesthesia and recovery.

For additional information regarding anesthetic use in fish please consult an ARP veterinarian or the following references.

  1. Stetter MD: Fish and Amphibian Anesthesia. In Veterinary Clinics of North America: Exotic Animal Practice 4(1), January 2001; pp. 69-82.
  2. Burka JF, et al: Drugs in Salmonid Aquaculture - A Review. J. Vet Pharmacol. Therap. 20, 1997; pp. 333-349.
  3. Bowser PR: Anesthetic Options for Fish. In Recent Advances in Veterinary Anesthesia and Analgesia: Companion Animals, 2001. International Veterinary Information Service, Ithaca, NY.

The information and drug dosages presented in this website are intended as a resource for Pennsylvania State University research investigators. No guarantee of drug efficacy or safety is made nor must information obtained from this site be substituted for professional veterinary advice.