Fa08400.pdf

Use of Antibiotics in Ornamental Fish Aquaculture1
Introduction
the rate of bacterial infection so total loss of fish will be reduced.
Antibiotics are very useful additions to any fish-health manager's toolbox, but they are only tools Gram-positive Bacteria versus
and not 'magic bullets.' The ability of antibiotics to Gram-negative Bacteria
help eliminate a fish disease depends on a number of factors: 1) Does the problem actually have a bacterial Most bacteria that infect fish fall into one of two component? 2) Are the bacteria involved sensitive to groups - gram-positive or gram-negative. These the antibiotic chosen? 3) Are the proper dosage and groups are named based on their response to a treatment intervals being used? 4) Have other protocol called gram staining. Gram-positive bacteria contributing stresses been removed or reduced? stain blue, and gram-negative bacteria stain pink. They stain differently because each group has a Antibiotics, in and of themselves, do not cure a different type of outer structure known as the cell fish. Antibiotics merely control the population wall. This difference is important for the producer growth of bacteria in a fish long enough for its and aquaculturist because some antibiotics work better against gram-positive bacteria and others work better against gram-negative bacteria. Most bacteria Before antibiotics are even considered, sources that infect fish are gram-negative, including of stress such as poor water quality (including drastic Aeromonas hydrophila, Aeromonas salmonicida, temperature change), nutrition, genetics, and Flavobacterium columnare (which causes handling or transport must be removed or reduced. columnaris), Vibrio, and Pseudomonas species. (See Affected fish should also be examined for parasites. UF/IFAS Fact Sheets FA-14 Aeromonas Infections, Any of these factors may be the primary cause of FA-31 Vibrio Infections of Fish and FA-11 disease, as bacterial infections are often secondary responses to such management problems. Contacting gram-positive bacteria that cause disease in fish are a fish health specialist early during the disease Streptococcus. (See UF/IFAS Circular 57 outbreak will help identify contributing stressors and 1. This document is Circular 84, one of a series from the Department of Fisheries and Aquatic Sciences, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First published: January 2003. Major Revision: July 2006. Please visit the EDIS Web Site at
http://edis.ifas.ufl.edu.
2. Roy P.E. Yanong, Associate Professor, Tropical Aquaculture Laboratory, Ruskin, Department of Fisheries and Aquatic Sciences, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, FL 32611.
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For information on obtaining other extension publications, contact your county Cooperative Extension Service office. Florida Cooperative
Extension Service/Institute of Food and Agricultural Sciences/University of Florida/Christine Taylor Waddill, Dean.
Use of Antibiotics in Ornamental Fish Aquaculture A third group, the acid-fast bacteria, which includes Mycobacterium species, will not be selecting antibiotics. Producers of food fish have discussed in this publication because they are fewer options than producers working with considerably different from most other bacteria (see ornamental fish because the FDA has elected to use UF/IFAS Fact Sheet VM-96 Mycobacteriosis in Fish).
regulatory discretion to keep products intended for the treatment of aquarium fish available. Your fish Optimal Approach to Fighting
health specialist will be able to provide information Bacterial Infections
on legal constraints for specific antibiotics, information for correct dosages, proper methods of Most bacteria that cause diseases in fish are administration, and concerns about effluent from normal inhabitants of aquatic systems and, ordinarily, they do not cause a problem. However, fish that are stressed by one or more factors (such as temperature Proper Dosages and Treatment
changes, poor water quality, recent transport or Regimens: Pharmacokinetics
handling), may have compromised (less effective) immune systems, making them more susceptible to Although selecting the correct antibiotic is an bacterial infections. In addition, stress factors that important first step in controlling bacterial disease, compromise the immune system of fish may actually proper administration of any antibiotic for the favor bacterial growth, further increasing the risk of a recommended number of days is equally important. Your fish health specialist should provide you with instructions on the dose (amount of antibiotic to use), The ideal solution to bacterial diseases involves the frequency (how often) and duration (how long) it working with a fish health specialist to culture the should be administered (given), withdrawal time (if organism and to run sensitivity tests. 'Culture' refers applicable - this is the length of time required, after to growing the infective bacteria on a special type of the last dose of antibiotic has been given, that a media (or 'food'; usually agar or gelatin based), and producer must wait before selling the fish, and is 'sensitivity' refers to treating the bacteria with a usually more of a concern in food fish species) and series of antibiotics to determine which one will work any other relevant information. The technical term for best. Although culture and sensitivity tests generally the branch of medical science that determines all of take two or three days, they are, by far, the best these variables is 'pharmacokinetics'; defined as the methods for selecting an antibiotic that will study of how drugs are absorbed by, distributed successfully and economically treat an infection.
within, chemically altered within, and eventually excreted by the body (in this case, the body of a A fish health specialist should be contacted and given a complete history of the problem during the initial stages of the disease. The specialist will How are the pharmacokinetics of a specific provide instructions on submitting samples to a antibiotic scientifically determined? Firstly, different diagnostic laboratory (see UF/IFAS Fact Sheet concentrations of the selected antibiotic are tested against various bacteria in order to determine what concentration will work best against these bacteria. Next, the antibiotic is administered (given) in one of Affected fish should not be treated with any three ways: 1) by injection, 2) mixed in feed, or 3) in antibiotic until after a sample has been analyzed. The a bath treatment. Then, antibiotic levels in the body sample should include at least 3 to 5 fish showing (usually in the blood) are measured at different time typical signs of the disease. Fish that are submitted intervals after treatment. The purpose of these after they have been given antibiotics often provide measurements is to determine how long the antibiotic poor culture results. While waiting for the culture stays active in the body of the fish and whether or not results, the fish health specialist may suggest a the concentration in the body is high enough to kill or broad-spectrum antibiotic that can be used until culture and sensitivity tests have been completed.
Use of Antibiotics in Ornamental Fish Aquaculture mortalities. It is a good idea to train fish to eat a antibiotics have not been scientifically determined for prepared diet (i.e., one that can be used to incorporate most species of fish (and especially not for most antibiotics), so that, should it becomes necessary to ornamental species), good estimations of the activity use antibiotics, the fish will be more likely to eat the of many antibiotics have been determined from medicated food as it is familiar to them. clinical experience and from work with food fish. Following such guidelines for dosages and their Bath treatments: Although bath treatments are
corresponding treatment intervals (e.g., Table 1 ) a popular method of administering antibiotics, much more drug is required to achieve the desired result as compared to oral treatments or injections. In many Percent Active Ingredient
cases, even a large amount of antibiotic in the water does not guarantee that enough of it will get into the Many antibiotics commonly used for ornamental fish to be an effective treatment. At the same time, fish are sold by different companies; therefore, the excessive amounts of antibiotic in the water can percent of active ingredient will vary from product to increase the likelihood of water-borne bacteria product. This means that you may not have 100% of developing resistance to that drug. Furthermore, to pure antibiotic required for disease control. You need avoid poor water quality and any potential toxicity, to ask your supplier to provide you with the actual between 70% and 100% of the water should be percentage of antibiotic that is active in the product changed at the end of each daily treatment and also you have purchased and calculate your dosage prior to redosing. Finally, bath treatments are not accordingly. For example, if your product contains recommended in recirculating systems or in any less than 100% of active ingredient, your dosage aquarium system where the treated water will contact needs to be increased to bring the level up to the the biological filter, because the antibiotics may kill equivalent 100% active ingredient. (See Equation 1) or inhibit the nitrifying bacteria in the biological If you are unsure how to do this calculation, call your filters (see UF/IFAS Fact Sheet FA-16 Ammonia). If treating fish in a bath, ideally a separate container should be used, or tanks and vats should be taken Major Routes of Administration
off-line during treatment. In summary, bath treatments should be considered only when the Injection: Injection is the most direct and
majority of the fish are not eating or when treating effective method for getting antibiotics into the blood primarily external bacterial infections and fish should stream. Unfortunately, this process is very labor be switched to oral medications as soon as they intensive and impractical for fish grown on a commercial scale. However, for small numbers of fish, or for important or expensive fish, injection may Consequences of Improper Dosage
and Treatment Time
Mixed in food: In aquaculture production, the
If the dose is too high or treatment times are too most cost effective and commonly used method to long, there is a danger of toxicity to the fish, deliver antibiotics is orally by mixing them into food. frequently causing liver, kidney, or other organ The proper dose of antibiotic is mixed into the feed damage that may or may not be reversible. during production, or else it is added after production, using fish oil or canola oil as a binding agent. The On the other hand, if the dose of antibiotic is too mixture is then fed to the fish for the prescribed low or treatment time is too short, the bacteria will number of days. Oral administration of antibiotics not be killed or weakened enough for the immune requires that most of the fish are still eating, so every system of the fish to remove them, and this greatly attempt should be made to catch bacterial diseases increases the risk of the bacteria developing early, before the majority of fish stop eating. Only resistance to the antibiotic. When bacteria become fish that are eating will be treated. Very sick fish that resistant to a specific antibiotic, even high are no longer eating will contribute to ongoing concentrations of that drug will not be effective.
Use of Antibiotics in Ornamental Fish Aquaculture Antibiotic resistance can also occur when greatly reduced efficacy at best and, at worst, they antibiotics are used improperly, such as the 'shot-gunning' method. 'Shot-gunning' involves administering one antibiotic after another to a Notes on Specific Antibiotics
population of fish, frequently at improper dosages, The following are some notes on specific for shortened treatment times, and without the aid of antibiotics used in the ornamental fish trade. Many of proper diagnosis (i.e., without culture and sensitivity them are strictly forbidden for use by food fish tests). If shot-gunning is used frequently at a facility, producers or are otherwise of concern to the Food resistance is almost certain to occur. In some cases, and Drug Administration (FDA). The FDA has the problem may not be due to bacteria, but rather elected to use regulatory discretion to keep products poor water quality or other management issues that intended for the treatment of aquarium fish available. have not been properly investigated.
Officially there are no FDA-approved antibiotics for While shot-gunning may work occasionally, treating ornamental fish. Therefore, should you have over time, it introduces too great a risk of producing any questions regarding the legalities of using any populations of bacteria that are resistant to multiple antibiotics, consult a fish health specialist. For antibiotics, which can result in the very real information on antibiotic use in channel catfish, possibility of a 'superinfection,' where the bacteria including specifics on use of oxytetracycline cannot be controlled with antibiotics. Once a system (Terramycin®) and Romet B®, see UF/IFAS Fact has a superinfection, it is usually necessary to Sheet VM-70 Use of Medicated Feed in Channel sacrifice the entire affected population, completely break down and disinfect the affected system, and Erythromycin is most effective against
start over. This is obviously not a desirable outcome. gram-positive bacteria, such as Streptococcus species. The importance of using antibiotics wisely (running The vast majority of bacteria that cause disease in culture and sensitivity tests, using proper dosages and fish are gram-negative, so erythromycin should only adhering to proper treatment times) cannot be be used after culture and sensitivity test results confirm it will be effective. Also, erythromycin is not Combining Antibiotics
very effective in a bath treatment, and it should only be administered by injection or in feed. Erythromycin Combining different antibiotics is generally not is not FDA-approved for use with food fish.
recommended. Antibiotics work at many different sites on and in the targeted bacterial cell. Using more The penicillins, including penicillin,
than one antibiotic can result in interference between amoxicillin, and ampicillin, are most effective
them and, as a worst case scenario, the antibiotics can against gram-positive bacteria such as Streptococcus essentially 'cancel each other out.' Most bacterial species; therefore, for the same reasons as those given infections can be treated effectively with a single above, these antibiotics are not a good first choice for most bacterial infections in fish. None of the penicillins are FDA-approved for use in food fish.
Proper Handling of Antibiotics
Oxytetracycline and related antibiotics are
When preparing or administering any type of considered broad-spectrum antibiotics (effective medication, it is always a good idea to wear gloves in against a wide variety of bacteria), and they work order to avoid unnecessary exposure to the user.
well when mixed with food. (See UF/IFAS Fact Sheet VM-70 Use of Medicated Feed in Channel It is important to use antibiotics that are as fresh Catfish.) However, bath treatments may not be as as possible and that have been stored properly. effective for all species. One study (Nusbaum and Antibiotics used after their expiration date or after Shotts, 1981) demonstrated that channel catfish being stored in hot and humid conditions will have absorbed approximately 15-17% of the oxytetracycline added to water with hardness of 20 Use of Antibiotics in Ornamental Fish Aquaculture mg/L and pH of 6.7. However, at least two freshwater None of the aminoglycosides are approved by fish species (yellow perch and hybrid tilapia) did not have the expected levels of this antibiotic in their blood when exposed experimentally to The quinolones, including nalidixic acid and
oxytetracycline as a bath treatment for up to 8 hours oxolinic acid are considered broad-spectrum
(K. Hughes, unpublished data; S.A. Smith, Virginia antibiotics, like the tetracyclines, and they work Tech, pers. comm. 2002; and R.P.E. Yanong, against a wide variety of bacteria. These antibiotics University of Florida, unpublished data). In addition, work best at acidic pHs of 6.9 or less, and they are calcium and magnesium bind to tetracycline and inhibited by hard water. Although they appear to oxytetracycline rendering them inactive. This means work well in both bath and oral treatments, some fish that with increasing water hardness (i.e., increases in may sink to the bottom and appear lethargic after bath calcium and magnesium levels), it is necessary to increase the dosages of these drugs in bath These antibiotics have been shown to damage the treatments. Tetracyclines are ineffective when used as nervous system of other animals and none are approved by the FDA for use with fish. Quinolones Tetracyclines are light sensitive, and they turn are closely related to a category of antibacterials brown when decomposing. This contributes to poor known as 'fluoroquinolones,' which are categorized water quality and may be harmful to the fish. Water as 'of high regulatory concern' by the FDA. Use of should be changed immediately after the bath fluoroquinolones or quinolones to treat any food treatment period is concluded. Due to years of animal is illegal and completely irresponsible.
misuse, several bacteria in many different facilities The nitrofurans, including nitrofurantoin,
are now resistant to tetracyclines. Oxytetracycline nitrofurazone, furanace, and furazolidone, are
still works adequately against most cases of commonly used in the ornamental fish trade, but the Flavobacterium columnare (columnaris disease).
FDA strictly forbids their use by producers of food Terramycin ® is a brand of oxytetracycline
fish. Nitrofurazone is specifically categorized as 'of manufactured by Pfizer that is FDA approved for use high regulatory concern' by the FDA and should not in the production of salmonids, channel catfish and be present at any facility where food species are lobsters (See UF/IFAS Fact Sheet VM-70 Use of Although nitrofurans are commonly used in bath The aminoglycosides, including gentamicin,
treatments, they are probably most effective against neomycin, kanamycin, and amikacin, are very
superficial infections and, in at least one study, effective against gram-negative bacteria infections nitrofurazone was not readily absorbed into the body when administered by injection. Unfortunately, this of either gilthead sea bream (Sparus aurata) or tilapia group has also been shown to cause kidney damage in (Oreochromis mossambicus) in experimental trials fish when administered by this technique. (Colorni and Paperna, 1983). Within the group, furanace appears to be the most effective for use in As a group, these antibiotics are not considered effective when used in oral or bath treatments. A couple of exceptions may be kanamycin and To achieve the most effective result when using neomycin, both of which may be effective against a nitrofuran in a bath treatment, either some sort of external infections if used in bath treatments. In cover or a darkened treatment location should be addition, kanamycin is also believed to be effective considered, as the nitrofurans can be inactivated by when mixed with feed to treat gastrointestinal light. Nitrofurans as oral treatments may not be as bacterial infections (Gilmartin, Camp and Lewis, effective as previously believed, although the proper pharmacokinetic research needs to be performed to verify this conclusion.
Use of Antibiotics in Ornamental Fish Aquaculture The sulfa drugs, including Romet®, are also
Carpenter, J.W., Mashima, T.Y. and Rupiper, considered to be broad-spectrum antibiotics. There D.J. 1996. Exotic animal formulary. First ed. are many different types of sulfa drugs. The more Greystone Publications, Manhattan, KS. 310 pp.
common sulfas are not as effective as they once were, due to their misuse or overuse resulting in the Colorni, A. and Paperna, I. 1983. Evaluation of creation of many bacteria that are now resistant to nitrofurazone baths in the treatment of bacterial them. On the other hand, the potentiated sulfas, infections of Sparus aurata and Oreochromis including Romet®, are still very effective. mossambicus. Aquaculture 35: 181-186.
Romet® works well when mixed with feed, but it does not work well as a bath treatment. It is Laboratory efficacy of amoxicillin for the control of FDA-approved for use with channel catfish and Streptococcus iniae infection in blue tilapia. Journal of Aquatic Animal Health 17(2):197-202.
Laboratory efficacy of amoxicillin for the control of Many bacterial infections in ornamental fish are Streptococcus iniae infection in sunshine bass. avoidable with proper management. However, if a Journal of Aquatic Animal Health 15:209-214.
population does become infected, it is important to Gilmartin, W.G., Camp, B.J. and Lewis, D.H. eliminate or reduce all contributing stresses. A fish 1976. Bath treatment of channel catfish with three health specialist should be consulted to assist with broad spectrum antibiotics. Journal of Wildlife proper diagnosis, to run culture and sensitivity tests, and to provide the best information regarding dosages and treatment intervals.
Kitzman, J.V. and Holley, J.H. 1989. Drug distribution and tissue concentration of gentamicin in Misuse of any antibiotic can lead to the creation the channel catfish. Proceedings, 29th Annual of resistant bacteria in a facility. In an attempt to Conference, International Association for Aquatic avoid this, some farms will rotate the antibiotics they Animal Medicine, San Antonio, TX. pp. 18-22.
use every few months or every year. However, the best solution is to positively identify the bacteria by Noga, E.J. 1996. Fish disease: diagnosis and running culture and sensitivity tests, and thereby treatment. Mosby-Year Book, Inc., St. Louis, MO. avoid unnecessary, costly and potentially harmful Absorption of selected antimicrobic drugs from water 'shot-gunning' can result in 'superinfections' in fish. by channel catfish, Ictalurus punctatus. Canadian These infections are caused by bacteria that are Journal of Fisheries and Aquatic Sciences 38: resistant to most of the commonly used antibiotics. Obviously, this situation is not desirable, and it is completely avoidable in most cases. Once it occurs, Post, G. 1987. Textbook of fish health. TFH however, little can be done to reverse the situation, Publications, Inc., Neptune City, NJ. 288 pp.
and the farmer is left with no treatment options other than depopulation of the fish followed by sterilization Stoskopf, M.K. 1993. Fish medicine. W.B. of the culture system and equipment or scrupulously Saunders Co., Philadelphia, PA. 882 pp.
Francis-Floyd, R., Petty, B.D., Pouder D.B., References
Yanong, R.P.E., and Watson, C.A. 2005. Two-day fish health management workshop. University of Florida/IFAS, Departments of Fisheries and Aquatic Sciences, CALS and Large Animal Clinical Sciences, CVM.
Use of Antibiotics in Ornamental Fish Aquaculture Stoskopf, M.K. 1988. Fish chemotherapeutics In Veterinary clinics of North America, Small Animal Practice: Tropical Fish Medicine, March. M. Stoskopf (ed). W.B. Saunders Co., Philadelphia, PA. pp. 331-348.
ANTIBIOTIC
ORAL (food) DOSE
BATH DOSE (water change recommended prior to each
189-378 mg per gallon every 3 days for 3 treatments 2.5 grams per 10 gallons every 3 days for up to 3 treatments 38 mg per 10 gallons for 24 hours, repeat as needed 95 mg per gallon for 15 minutes, repeat twice daily for 3 days 750-3,780 mg per 10 gallons for 6-12 hours, repeat daily for 10 days (dose will depend on hardness of water) Note: As a rule, oral/food treatments are more effective, more efficient, less detrimental to water quality, and preferable to bath treatments; remember, bath treatments may hurt biological filtration. Also, some of these drugs are available locally in premixed medicated foods.
Dosage references: Carpenter et al. 1996; Darwish and Hobbs 2005; Darwish and Ismaiel 2003; Noga 1996; Post 1987; Stoskopf 1988; and University of Florida. Use of Antibiotics in Ornamental Fish Aquaculture Equation 1.
To determine the correction factor for an antibiotic that is not pure (i.e., is not 100% active ingredient) use the following: Where P is the percentage of active ingredient.
Example:
To calculate the correct oral dose of tetracycline with 50% active ingredient using Equation 1Dosage rate (from Table 1 above) is 1.12 grams/lb of food and P is 50Therefore, Correction factor = 1.12 x 100/50First divide 100 by 50, which gives you 2Then multiply 1.12 by 2 to get 2.24This means with 50% active ingredient of tetracycline, you need to dose with 2.24 grams/lb of foodThis makes sense- you have to use twice as much since your antibiotic is only half strength (50%)

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