Fish Medicine and Surgery in the Private Practice
American Association of Zoo Veterinarians Conference 2008
Natalie D. Mylniczenko, MS, DVM
Brookfield Zoo, Brookfield, IL


According to the American Pet Products Association in 2007 142 million freshwater fish and 9.6 million saltwater fish were owned in the U.S. Many of these fish owners are bonded closely with their pet and can become frustrated when they cannot find a veterinarian to help with their wet companion. 'Ability' doesn't prevent a small animal clinician from seeing fish-owning clients, merely lack of familiarity and the difficulty organizing their practice to accommodate these individuals. This presentation shows the private practitioner that fish medicine is approachable and that they can provide a great service to fish owners. With these simple suggestions all veterinarians can begin seeing clients with fish.

Reference Library

Fish literature is vast and a review here is impractical. Some texts are more accessible and recommended for the clinician who does not have any fish medicine texts.1,7,11 There is a more complete reference list at the end of this document.

Practice Set Up

Basic Equipment8,12

Water Quality Testing 'Lab'

Understanding water quality in fish systems is paramount as the health of the water media fish live in is directly correlated to their health. It is not as intimidating as it might appear and several texts do an excellent job explaining it.1,6,7,11,14 Testing can be elementary or state-of-the-art, depending on the volume of testing you will be performing. The lower-cost kits will not give accuracy, but will give you a good idea of the general condition of the environment and be adequate to diagnose poor water conditions. Perform on-site testing as a routine to your visit; if the animal is at your clinic, make sure clients bring in at least 250 ml (~1 cup) of water (from the tank, not the bag the fish is transported in) for in-house testing. The minimum water quality database includes: temperature, pH, ammonia, nitrite and nitrate. Dissolved oxygen measurements are ideal but difficult to get accurately or easily. Salinity (usually as specific gravity) should be measured with saltwater tanks.

Animal Life Support2,11,14

Be prepared to anesthetize and recover your patient. Request that owners bring in additional tank water to recover the patient. The set up for fish anesthesia is diverse and ranges from simple, such as a moistened sponge or other soft material, to a more advanced set up involving submersible pumps, aquaria and a working platform. Animals should be ventilated by a simple syringe and catheter/soft tube or a pump driven apparatus that guides water over the gills.


A standard light microscope and associated materials (slides, coverslips) are necessary.

Animal Transport

You will have to decide if the animal will come to you or if you will go to them. Many factors go into this decision: your time, animal history directing diagnostic needs (radiographs for instance), animal size, degree of illness. Seeing the animals in their environment gives you insight into daily care and the condition of the other animals in the habitat; seeing animals in practice gives you flexibility to available resources. Details on appropriate transport techniques are available.6,12


Wear latex gloves that have been rinsed in dechlorinated water to remove the powder. Manual restraint may be appropriate if the procedure has low impact on the fish or requires only a short period of time. Anesthesia may be required for excitable fish, small fish, and delicate or lengthy procedures. The most common drug is tricaine methane sulfonate (MS-222 (Finquel), Argent Chemical Laboratories, Redmond, WA) buffered in an equal weight of sodium bicarbonate. Note that an excitatory does typically occur and animals may jump from the water. General doses for sedation are 25-50 mg/L for light sedation or 75-100 mg/L for heavier sedation. See other texts for detailed information regarding fish anesthesia and physiology.2,11,14

Basic Diagnostics9,12

With all of the excellent references available, even the novice fish veterinarian can make accurate diagnoses and will be able to help the client in need.

Water Quality

Reference ranges vary with species but are generally: dissolved oxygen 5-10 mg/L, pH 6.0-9.0 (need to know the species requirements), unionized ammonia < 0.05 mg/L, nitrite < 0.10 mg/L, and nitrate < 20 mg/L (large variation with this parameter). Refer to texts for variation within species and clinical manifestations.

Skin scrapes, fin clip, gill clips and lesion impressions are all simple procedures. Samples can be prepared for three slides for each location (in order of importance): 1) wet mount (using transport water), 2) routine staining for cytology and 3) acid fast staining (especially non healing wounds). Wet mounts must be viewed immediately in order to observe protozoal motility which will help with diagnosis.

Other techniques include fine needle aspiration of masses, and fecal examination (opportunistic or by colonic lavage). Blood collection is an option to consider, however size of animal may preclude meaningful sample size and interpretation of results can be challenging.4,12 Reference ranges are not readily available for all species but are available for goldfish and koi.5

Imaging techniques such as radiography and ultrasound can be very useful in providing a diagnosis.

Microbiology can be an invaluable tool in fish medicine. Blood cultures in teleosts are very useful in diagnosing septicemia. Post-mortem samples of the caudal kidney will also be important, particularly for group health. Samples of lesions should be obtained carefully, avoiding the mucus because of the copious amounts of normal flora; clean deep cultures may be necessary.

Post mortem exams, even if performed in-house, are an excellent method to get some diagnostic answers.16 Submission of samples for histopathology may be warranted. In those cases the samples should be fresh as fish autolyze rapidly in water. Finding a pathologist with fish experience is important.


Environmental diseasesare the number one reason that fish (like other exotic animals) will be present with illness. Parasites are the second most likely disease issues. Bacterial disease, trauma, ocular and buoyancy disorders are other typical disease. Viruses in pet fish are usually limited to lymphocystis. Detailed clinical presentation for all these disease, diagnosis and treatment strategies are found in the typical texts.11,14


Don't shy away from surgery! Conditions necessitating surgery will include mass removal, ocular enucleation, reproductive surgery, swim bladder repair, and celiotomy for exploration. Advanced techniques might include laparoscopic surgery and laser surgery. Post-operative management might require antibiotic therapy or analgesics. With some minor adjustments, you can safely perform most of the necessary procedures and prolong the life of these wet patients.


This may be the most difficult thing you will have to consider in the management of your fish patients. Is isolation a possibility at the home? If not consider placing a separate floating basket to manage animals in their home tank. This basket should provide shelter and good water flow. By separating the animal there will be easier observation and treatment compliance can be noted. Formularies are available to assist in making decisions regarding pharmacotherapeutics.3,11,14 If the animal is eating then this should be the first option. It is likely though that the patient will not be interested in consuming food or oral treatments and other options should be considered. As with any patient, client ability to administer medications and animal condition will direct your decision. The option of immersion in medication is one that is usually unavailable to terrestrial patients; however consideration for tank mates and tank health must be present as some immersion treatments will damage the bacterial filter of the tank. Short immersions scan then be considered in a separate container.

Client Education

Once a client learns of your interest it is likely they will seek you out regularly and early in the course of disease. At the onset however, be prepared to be the last one on the list. That being the case, it is critical to counsel your client on the prognosis of the case; animals that present to you debilitated are less likely to be successful outcomes. Anesthesia and handling with these critical animals may result in the death of the fish. Explaining risk vs. benefit of attempting treatment or diagnosis will be crucial for return clients.

Emergency and Critical Care

Most of the assistance you will likely be able to provide will be over the phone. Depending on the source of the emergency, you may have to guide your client to perform some at home techniques. These can be adding additional sources of air (by way of an air stone), water changes (with appropriate immediate dechlorination using sodium thiosulfate and temperature equilibration) or managing temperature. There are certainly a myriad of possible scenarios, prepare yourself ahead by reviewing some helpful literature.6

Zoonotic Disease

Familiarizing yourself with aquatic borne zoonosis is no different than with other exotic pets. The following organisms are of concern: aeromonads, vibrios, Enterobacteriaceae, mycobacterial species, Erysipelothrix rhusiopathiae, Streptococcus iniae, Edwardsiella tarda, among others.9


Euthanasia of fish is one the most common reasons an owner will call in desperation. While they hadn't considered calling the veterinarian for treatment, they don't know who else to call for assistance in humanely ending their pet's life.

Acceptable methods for humane euthanasia:

1.  Anesthetic overdose with buffered MS 222 [Tricaine methanesulfonate] at >250 mg/L for at least 10-15 minutes. Other anesthetic overdoses are also appropriate and may include clove oil or benzocaine (

2.  Carbon dioxide overdose: two tablets of Alka-Seltzer® per liter of water (or 8 tablets per gallon).11 Advise the client that the animal will react physically, but that the procedure will be rapid. This method, while not as palatable as an anesthetic overdose, is more appropriate than the following alternatives.

3.  Decapitation, followed by pithing.

Unacceptable Methods:

1.  Freezing

2.  Flushing

3.  Boiling

4.  Electrocution (except individuals specially trained)

Continuing education and participation in aquatic focused organizations will only improve your skills and expose you to a very fascinating and fun field of veterinary medicine. Fish medicine is unique, creative and can be an important service to your community.


1.  Andrews, C. A. Exell, and N. Carrington. 2003. Manual of Fish Health: Everything You Need to Know About Aquarium Fish, Their Environment and Disease Prevention. Firefly Books, Ontario, Canada.

2.  Bowser, P.R. 2001. Anesthetic Options for Fish. In Recent Advances in Veterinary Anesthesia and Analgesia: Companion Animals, R. D. Gleed and J. W. Ludders (Eds.). International Veterinary Information Service (, Ithaca, New York, USA. Accessed from on August 30, 2008

3.  Carpenter, J. 2005. Exotic Animal Formulary. W.B. Saunders. WB Saunders, St. Louis, MO.

4.  Clauss, T.M., A. D.M. Dove, and J.E. Arnold. 2008. Hematologic Disorders of Fish Vet Clin North Am Exot Anim Pract. 11(3):445-462.

5.  Groff J.M. and J.G. Zinkl. 1999. Hematology and clinical chemistry of cyprinid fish. Vet Clin North Am Exot Anim Pract. 2(3):741-776.

6.  Hadfield, C.A., B.R. Whitaker and L.A. Clayton.2007. Emergency and Critical Care of Fish. Vet Clin North Am Exot Anim Pract. 10(2):647-675.

7.  Hiscock, P. 2000. A Practical Guide to Creating and Maintaining Water Quality. Interpet Publishing. Surrey, UK.

8.  Klinger, R., Francis-Floyd, R., Riggs, A., and Reed, P. 2003. Use of blood culture as a nonlethal method for isolating bacteria from fish. Journal of zoo and wildlife medicine 34(2):206-7.

9.  Lewbart, G.A. and M. A. Stamper. 2005. Standard of care: pet fish. The North American Veterinary Conference Proceedings. Accessed from on August 30, 2008.

10. Lowry, T. and S. A. Smith. 2007. Aquatic zoonoses associated with food ornamental, and tropical fish. J Am Vet Med Assoc 231(6): 876-80.

11. Murray, M.J. 2002. Fish Surgery. Seminars in Avian and Exotic Pet Medicine. 11(4):246-257.

12. Noga, E. J. 1999. Fish Disease: Diagnosis and Treatment. State University Press, Iowa City, IA.

13. Reavill, D.R. 2006. Common Diagnostic and Clinical Techniques for Fish. Vet Clin North Am Exot Anim Pract. 9(2): 223-235.

14. Reavill, D.R. and H. Roberts , 2007. Diagnostic Cytology of Fish. Veterinary Clinics of North America: Exotic Animal Practice. 10(1): 207-234.

15. Stoskopf, M.K. 1993. Fish Medicine. W.B. Saunders Company, Philadelphia, PA.

16. Yanong R.P.E. 2003. Necropsy techniques for fish. In: Practical Gross Necropsy of Exotic Animal Species. Seminars in Avian and Exotic Pet Medicine, Echols S., ed. W.B. Saunders Co., Philadelphia, PA. 89-105.

Speaker Information
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Natalie D. Mylniczenko, MS, DVM
Chicago Zoological Society/Brookfield Zoo
Brookfield, IL, USA