Judicious Use of Antimicrobials for Treatment of Aquatic Animals by Veterinarians

Comment on this policy

Aquatic veterinarians are expected to use all therapeutants, including antimicrobials, judiciously. Judicious use of antimicrobials for aquatic animals is necessary to:

  • Restore aquatic animal health;
  • Protect the economic livelihood of commercial facilities;
  • Ensure the continued production of foods of animal origin;
  • Minimize development of antimicrobial resistance in animal pathogens;
  • Minimize development of antimicrobial resistance in human pathogens; and
  • Minimize the shedding of zoonotic pathogens into the environment and potentially into the food chain.

In addition to awareness of, and adherence to AVMA's Judicious Therapeutic Use of Antimicrobials guidelines, the following are specific recommendations for the antimicrobial use in aquatic animals.


Judicious Antimicrobial Use Principles

The aquatic veterinarian should:


  • Accept responsibility for helping clients design health management programs, including for individual animals and/or populations or stock general populations, including immunization and nutrition programs, that will reduce the incidence of disease, and the need for antimicrobial treatment.

    Development and implementation of appropriate disease prevention through effective vaccination is likely to reduce the incidence of disease and subsequent need for antimicrobial treatment. When there is an increased disease incidence, efforts to identify and correct immunosuppressive factors should be implemented. Ensuring high quality nutrition is of paramount importance and will provide general as well as immune-related health benefits for all life stages. Optimal nutrition can lead to a reduction in morbidity and mortality with a consequent decrease in the need for antimicrobial treatment. Water source quality should be evaluated, including an assessment of the potential disease transmission risk from feral populations and the related need for biosecurity measures to protect captive populations. This will help to prevent the introduction of additional pathogenic microorganisms that could cause diseases requiring antimicrobial treatment. Veterinarians should work closely with other aquatic animal health experts employed at the facility in the design and implementation of health management programs.

  • Use antimicrobial drugs only within the confines of a valid veterinarian-client-patient relationship, including both the dispensing and issuing of prescriptions and veterinary feed directives. Extra-label usage should be consistent with regulatory agency laws, regulations and policies.

    The veterinarian must:
    – Be either the person responsible for diagnosis of disease conditions in an aquatic animal facility or be working directly with a fish health professional at the facility;
    – Be available for questions or concerns following treatment with antimicrobial drugs; and,
    – Accept responsibility for health care of the aquatic animals on that facility.
    – Have familiarity with the facility through previous visits to the premises.
    [see VFD and ELDU requirements]

    Under these circumstances, the veterinarian will be able to make a recommendation on appropriate antimicrobial drug treatment and minimize the development of antimicrobial resistance. Veterinarians prescribing, dispensing or administering antimicrobials to aquatic animals should utilize the services of unbiased and reputable sources (e.g., Food Animal Residue Avoidance Databank) to provide scientifically sound withdrawal times for food animal producers.

  • Properly select and use antimicrobials. Veterinarians should participate in continuing education programs that include information on therapeutics and emergence and/or development of antimicrobial resistance.

    Antimicrobial resistance concerns, including the transmission of human safety food borne resistant microorganisms and/or resistance determinants and human pathogen antimicrobial resistance, are discussed at numerous regional, state and national meetings every year. At least some portion of the required continuing education hours should be received on the topic of antimicrobial susceptibility of animal and potential zoonotic pathogens. Material accessible from reliable sources such as the FDA/CVM, FARAD, AVMA home pages, and from the many available additional sources of professional information, should be incorporated into treatment considerations and recommendations. Many aspects of aquatic animal health management, including nutrition and immunology, are topics of active research. Veterinarians should stay current in their knowledge of this research in order to develop effective disease control programs.

  • Have strong clinical evidence of the identity of the disease etiology, based upon history, clinical signs, necropsy, laboratory data, and/or past experience before recommending antimicrobial treatment.

    Records and observations on individual animals or within populations, such as ponds, tanks, pens and raceways within a veterinarian's area of practice may be very helpful in developing antimicrobial treatment recommendations. Historical diagnostic material obtained from post mortem and moribund aquatic animal examinations may also be helpful. Diagnostic data reports are a useful barometer of changes in pathogen sensitivity patterns, although susceptibility profiles may be skewed (perhaps due to prior therapy). The status of the originating facility should be considered when establishing a diagnosis in disease outbreaks and when selecting a treatment protocol. Proven biosecurity measures should be implemented when aquatic animals are introduced to a facility to reduce the need for antimicrobial therapy.

  • Treat aquatic animals with antimicrobial according to the product label (including indication, dosage, frequency, duration, method of administration, species and environmental conditions).

    The product label recommendations are established through sound scientific data. Veterinarians should follow these recommendations instructions (e.g. "top-coating" or "top-dressing" of feed is not among the currently approved formulation methods). Furthermore, the goal of therapy should be to reduce fish mortality and minimize disease recurrence. Veterinarians should strive for the lowest dosage and appropriate frequency and duration of treatment that achieves these goals. Veterinarians should rely on previous medical records and valid published information to support clinical judgments on the proper time to discontinue therapy. The antimicrobial drug label may require specific waste handling, or may limit the concentration allowed in production facility effluent water. The veterinarian should assure that the antimicrobial- containing waste or effluent is handled according to the product label directions. The veterinarian should also assure that the production facility complies with appropriate federal, state and local laws and regulations (e.g., National Pollutant Discharge Elimination System permits) applicable to antimicrobial use and discharge before authorizing antimicrobial administration. Withdrawal times in food animals should also be monitored for compliance.

  • Choose an antimicrobial and treatment regimen based on available laboratory and label (including package insert) information, additional data in the literature, and with consideration of the pharmacokinetics, spectrum and pharmacodynamics of the antimicrobial.

    When this information is combined with the clinical and laboratory information previously mentioned, prudent and judicious antimicrobial use decisions are possible. The label dose, route, frequency and duration should be followed except where extralabel drug use is necessary and falls within laws, regulations and policies. Familiarity with extra-label drug use requirements is essential given the limited availability of approved antimicrobial drugs for aquatic animal use.

  • Use antimicrobials with a specific clinical outcome(s) in mind, including a specific target for population morbidity and/or mortality rate reduction.

    Specific outcome criteria prevent unnecessarily long therapy and indicate when the current therapy is ineffective. A timeline for expected results should be included in the treatment protocol.

  • Determine population pathogen susceptibility at the first indication of increasing morbidity or mortality and monitor the therapeutic response to detect changes in microbial susceptibility and to evaluate antimicrobial selections.

    If the specific outcome criteria are not being met within the expected timeline, the diagnosis and treatment protocol should be re-evaluated by the veterinarian.

  • Routine necropsy examination of aquatic animal populations should be periodically performed, including antimicrobial susceptibility testing, to update historical information for developing treatment and control protocols.

    This will provide information on changes in pathogens in the population and indications of drug antimicrobial resistance development by the pathogens.

  • Use products that have the narrowest spectrum of activity and known in vivo effectiveness against the pathogen causing the disease problem.

    In clinical situations, the boundary between a narrow and broad spectrum of activity may be difficult to determine. Narrow and broad spectrum levels of activity will vary depending upon the bacteria affected by the antimicrobial drug and the treatment regimen chosen. In spite of the difficulty in confining antimicrobial use to a narrow spectrum of activity, resistance to antimicrobials should be minimized by selecting an antimicrobial with a narrow spectrum of activity whenever possible. The aquatic animal veterinarian presently has access to a very limited armamentarium of antimicrobials. However, this situation may change as new products are developed and approved. The veterinarian needs to be attuned to the potential for change.

  • Choose antimicrobial of lesser importance in human medicine, if these receive future aquatic animal use approval, and do not choose an antimicrobial for which emergence of resistance is expected to be in an advanced stage.

    Antimicrobials that are of lesser importance in human medicine should be chosen when considering extralabel use of newer generation antimicrobials. This is of particular concern if the extralabel drug is in the same class as a human antimicrobial that may be the primary or sole treatment for a human infection. New antimicrobials should be reserved for cases that can be predicted to be refractory to other therapies and should be used according to label directions or extralabel drug use regulations.

  • Use, whenever possible, an antimicrobial labeled to treat the condition diagnosed.

    The veterinarian should work with clients to ensure that appropriate diagnostic procedures are in place to evaluate disease causation and initiate the appropriate antimicrobial therapy when indicated.

  • Ensure proper antimicrobial use at the facility and protect antimicrobial integrity through proper handling, storage and observation of the expiration date.

    Each drug held at a client's facility should be properly labeled, stored in a secure location at the proper temperature, and used according to instructions before its expiration date, and appropriately disposed of if past the expiration date on the drug label.

  • Prescribe, dispense or write a Veterinary Feed Directive for antimicrobial quantities appropriate to the production-unit size and expected need using the approved formulation.

    The amount of a particular antimicrobial prescribed or written in a veterinary feed directive should be consistent with the diagnosed disease and treatment requirements. If the antimicrobial is not dispensed by the veterinarian, then good communication between the veterinarian, animal producer, feed mill and/or pharmaceutical distributor is essential. This communication needs to be coupled with the appropriate prescription or veterinary feed directive and correct medicated feed labeling to ensure proper antimicrobial usage. The prescribing veterinarian should seek to review or receive copies of invoices of scripted antimicrobial purchases to ensure that appropriate quantities are being purchased for use.

  • Work with facility aquatic animal health management personnel to ensure that facility personnel receive adequate training on the use of antimicrobials including indications, diagnosis, dosages, withdrawal times, route of administration, storage, handling, and accurate record keeping.

    The veterinarian should ensure that labels are adequate to instruct facility personnel on the correct use of antimicrobials. The veterinarian should provide training to facility personnel on proper antimicrobial administration.

  • Work closely with all other health experts involved in aquatic animal population health management at the facility.

    Veterinarians are encouraged to work with clients to develop written standard operating procedures for initiating disease diagnostic activities and implementing treatment. Those protocols should include specific procedures to follow when administering antimicrobials at aquatic animal facilities.

The aquatic veterinarian should also follow the principles of:

  • Not using combination antimicrobial therapy unless there is information to show that this decreases or suppresses target organism resistance development as there are no scientific data currently available to indicate that combination antibacterial therapy is beneficial with the few antimicrobials labeled for use in aquatic animals.


  1. Anonymous. The Medical Impact of the Use of Antimicrobials in Food Animals. Report and Proceedings of a WHO Meeting, Berlin, Germany, 13-17 October 1997. WHO, p. 1, 1998.
  2. Committee on Drug Use in Food Animals, NRC/IOM. The Use of Drugs in Food Animals: Benefits and Risks. National Academy Press, p. 65, 1999.
  3. AVMA Aquaculture and Seafood Advisory Committee. Extralabel Use of Medicated Feeds for Minor Species. Journal of the American Veterinary Medical Association, 225(4):531532, 2004.
  4. Haskell, S.R.R., K. Carberry-Goh, M.A. Payne and S.A. Smith. 2004. Current status of aquatic species biologics. Journal of the American Veterinary Medical Association 225(10):1541-1544.
  5. NCCLS. Methods for Antimicrobial Disk Susceptibility Testing of Bacteria Isolated from Aquatic Animals; a Report. NCCLS (National Committee for Clinical Laboratory Standards) document M42-R . Clinical and Laboratory Standards Institute, Wayne, PA.

Reference Guide:

Antimicrobials for Aquatic Veterinarians, Judicious Use of (PDF)