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Antibiotics and the treatment of bacterial disease causing ulceration in Koi
There are more fish species in the oceans and seas than we can count and, as most diseases are host specific and given the water volume per fish, they should be safe. However, all fish species can suffer from the health problems that are triggered by the environment they live in and the seas and oceans are becoming polluted making the long term survival of many species uncertain. A pond, in comparison, is an unnatural body of water and this means the risks can be greater as pollution can exist in various forms. Koi need a pond that is biologically and chemically balanced or they too can become victims of their environment. Currently there is an increase in the number of outbreaks of bacterial disease in Koi and investigations carried out at LFH laboratories suggest this is cause for concern.
The basics
It is well known Koi must live in optimum pond conditions and Koi keepers need an understanding of pond water chemistry. Those new to the hobby often fail to get the appropriate guidance and water parameters are assumed to be acceptable without tests being carried out. Dissolved oxygen levels are far more important to Koi well-being and pond biology than is realised. The assumption is that water returning to the pond from a filter or waterfall introduces oxygen when an air pump and air stones creates oxygen already dissolved in the water that can access the gills far more effectively. As pond stocking levels increase and Koi grow larger, their dissolved oxygen requirement rises and, if this is overlooked, the fish will not thrive in high levels of carbon dioxide. Filters contain organisms that also need oxygen leaving the Koi to get by on whatever is left. Pond filtration systems have to be managed hygienically to keep disease at bay and it is a fact that the popularity of Koi results in overstocked ponds adding to the risk of health problems. Choosing a dealer that fully quarantines Koi on import is another vital aspect of pond management as it only takes one new Koi to introduce disease and Koi keepers can be tempted by attractive Koi with unknown origins.
Ulcer or abrasion
Bacteria cause various diseases in Koi; however, this article focuses on the most common form which is ulcer disease. Skin ulcers are often mistaken for injuries caused by rocks and plant baskets. However, should such an injury occur to one Koi, others would not make the same mistake as they are very alert to danger. An abrasion is minor skin damage that can happen if Koi continually relieve irritation due to poor water quality or skin parasites by flicking on the pond wall or floor. Spawning can also cause bruising and abrasions and minor damage can heal without intervention. When only one fish has slight skin damage, this does not indicate disease. However, when several Koi all show signs of a skin abnormality, that could be a sign that an ulcer bacterial disease is more likely.
Sources of infection
New Koi can be the source of certain diseases however, they are not high on the list of factors in the increased level of ulcerative forms of bacterial infection. When a new Koi is the culprit, in most cases the water temperature would be in the spring or summer temperature range or the pond heated for disease to develop. The new Koi will be the first fish to show signs of an ulcer and, gradually over a few days, other Koi could become infected. Skin damage can occur when a new Koi is transported and introduced to a pond and in such cases bacteria in the water can be responsible for an ulcer and tracing the origins of a disease is rarely straightforward. However, the prime trigger for a rise in the number of cases of ulcer disease is filter maintenance methods. It is important not to allow harmful bacteria harboured in filter systems to enter the pond and the safest method is to flush the water from the filter to waste for several minutes after all filter maintenance procedures. Once this is completed, it is safe for water to flow back to the pond. Some systems have a non-return valve in position to make this easier. If the bacteria are not flushed to waste and the water is in the spring or summer temperature range or the pond heated it is possible several Koi could show signs within a few days of filter maintenance. Initially this will appear as a mild infection although, if unnoticed, it can become more serious.
Bacterial attack
Many outbreaks of ulcerative disease occur in spring as water temperatures rise although the infection can spread more quickly in the summer. Whilst various bacterial species can be involved in ulcerative disease it is primarily Aeromonas strains that are isolated. A strain is a subset of a bacterial species and the Aeromonas family is comprised of strains in what is termed the Aeromonas complex. It is these variations that can complicate the sensitivity to antibiotics and this explains why one antibiotic cannot cure every disease outbreak. To add to this complexity, if several species or strains are isolated, more than one antibiotic might be needed. The production of beta lactamases by members of the Aeromonas family are associated with antibiotic resistance creating potential problems in treating infected Koi and this endorses why disease prevention is far more successful than all attempts to cure it.
Aeromonas
Motile Aeromonas are water borne bacteria that take up residence on the skin in the mucus layer of Koi searching for nutrients. Biochemical interactions take place in the mucus in the early stages of the disease and proteins present assist bacteria in their aim to infect the Koi. Stopping this activity by applying an iodine-based product such as Tamodine as soon as an ulcer is observed can help and this can be repeated every 2-3 days on and around the ulcer. The ulcer should turn white around the edges and this white area should slowly extend towards the centre of the ulcer. Ultimately, the whole area will become white and glossy although the normal skin colour can take a while to return depending on the level of damage. Treating the pond with Chloramine T if the filter is known to withstand chemicals is also advisable when the ulcers are treated. If caught in the early stages, a more serious form of disease is avoidable. The timescale for the disease to progress from spotting an ulcer to the fish becoming seriously ill varies with the pond conditions and will be faster at higher water temperatures. It is the Koi keepers’ ability to manage the disease that decides how the fish will progress. Success is often measured in the short term when ulcers heal but this does not mean that the disease has been completely cured as outbreaks often reoccur.
The Antibiogram
If the treatment is too late and the disease enters a more serious phase, antibiotics may be needed. It is vital they are used for serious disease and not to treat minor abrasions as their use adds to antibiotic resistance. In ponds where an antibiotic is used too often, the day will arrive when it is no longer effective. Accurate diagnosis requires a post-mortem examination however, it is possible without sacrificing a fish to take a swab from an open ulcer. A swab resembles a cotton bud although the tip is not cotton as this destroys bacteria. Accompanying the swab is a tube with preservative to keep the bacteria viable in transit. The swab must be taken in a satisfactory way to detect the primary pathogen as mucus and skin debris can flaw the result. The swab is sent to a laboratory for an antibiogram, a process that identifies the specific pathogens causing disease and also determines the most sensitive antibiotic in its treatment. Bacteria is processed differently depending on the type of laboratory. An aquatic laboratory will have experience of the pond environment and the commensal organisms that live in it as well as knowledge of host specificity and the incubation criteria for numerous fish diseases. For example, E. Coli causes disease in humans yet is isolated from pond water in which the Koi are healthy. In some laboratories, bacteria are cultured to obtain colonies on a sterile growth medium, the choice of medium depending on the suspected organism, and the temperature at which incubation will take place. Tryptone soya agar is often used in fish microbiology and is incubated at 22°C which is a low temperature compared with a hospital laboratory. Each individual bacterium can produce a large colony of organisms after 24 hours in incubation.
Methods vary
For many years the properties bacteria possess have been used to identify them as they vary in shape and size and produce substances exclusive to their various groups. When exposed to special reagents these substances initiate a colour change that codes for a specific bacterial strain. Once cultured colonies of bacteria are placed in a sterile saline solution and the resulting bacterial suspension is applied to the surface of various types of agar depending on the suspected pathogen. Discs impregnated with various antibiotics are spaced apart on the agar and incubated. In the case of Koi these antibiotics will be fish safe and will vary from those in use in a hospital laboratory. The result will be clear circular areas around the discs that have inhibited the bacteria, and as the discs vary in antibiotic volume this suggests the dose level required. An antibiogram report is then issued with the results. However, technology is in use in some laboratories that shortens the incubation time and provides a faster result and we can offer this expedited bacteriology service at LFH laboratories.
Which antibiotic?
In many ponds, antibiotics are administered without a treatment plan and this can lead to failure. An inappropriate antibiotic for the disease, the wrong dose level, and poor injection techniques can all result in no improvement in the fish. Reliance on antibiotics has created bacteria that are resistant to their use and this is now a major problem in all branches of medicine. Using an antibiotic with the potential to damage the major organs in Koi is something that hobbyists sometimes resort to without realising the risks. The fish may survive the treatment only to succumb at a later date to complications due to the antibiotic. The illegal sales of antibiotics on the Internet do not help the resistance and misuse issues. Injection techniques can be extremely poor causing abscesses, fin loss, and even damage to the heart when an inappropriate site is used.
Obtaining antibiotics
No fish species is covered under the Veterinary Surgeons Act and this means vets do not have to prescribe antibiotics for fish. If a vet states that he cannot help a Koi keeper, another vet can be approached. When a vet indicates he or she may be able to help, a professional judgement has to be made that the request for an antibiotic is not for ongoing disease as this is an environmental issue. Vets must also consider the antibiotic resistance crisis. This means that there will be many cases when antibiotics cannot be prescribed for Koi or other fish species. At LFH laboratories, we issue a report on health investigations that require an antibiotic and discuss our findings with our clients’ vet.
Effective use of an antibiotic
With adult Koi a course of injections is the effective method of treatment as this is the only way to provide fish with a therapeutic dose level of the antibiotic. With very small Koi or when there is a large volume of fish to be treated, the oral route may be the only option. However, impregnating food with an antibiotic is not a successful method as it fails to provide the required dose to every Koi and the disease is likely to be ongoing. There are exceptions, although in the vast majority of cases, an injectable antibiotic is inappropriate for coating fish food, and an oral formula antibiotic is not suitable for injection. It is not advisable to use two different antibiotics at the same time without professional advice as there can be conflicts. To use antibiotics effectively, follow a planned approach to the treatment. The stress of netting, sedating, and injecting fish must also be considered at the outset of the treatment, as extremely sick fish particularly those that are not taking food are less likely to survive and in extreme cases euthanasia is the humane option.
Administering antibiotic
Administering one injection only works with very specific types of antibiotic and a course of injections is the norm although the antibiogram findings are the guide. Whilst there are various routes for other drugs, most antibiotic injections should be administered into the muscle accessed immediately behind the dorsal or back fin where the fin meets the body. This is a safe injection site that avoids the considerable body damage that occurs in other locations and also less injectant is expelled. The syringes that are best for Koi are 25-28 gauge or those used for human insulin. When only one or two Koi have ulcers, the antibiotic is administered only to them and the unaffected Koi are not treated at this stage as it is possible they are not yet infected. The fish that as yet do not have any signs of disease are observed and treated with the antibiotic if and when they too develop ulceration. However, in a situation when the majority of Koi in a pond all have ulcers then they all need a course of antibiotic as the spread of the disease is advanced. It is not possible to prevent disease in the way a vaccine does by administering an antibiotic as Koi that appear healthy can contract disease at a later stage.
As mentioned previously, an iodine based product is the recommended treatment at the first sign of an ulcer. When carrying out a course of antibiotic injections, it is better not to apply too many layers of various products as this can interfere with the healing process. When giving the first injection, apply only iodine such as Tamodine by Vet Ark Ltd. Do not use any other products directly on to an ulcer when giving the subsequent injections. The stress of netting, sedating, and injecting fish must also be considered at the outset, as extremely sick fish are less likely to survive. Open ulcers allow vital fluids containing electrolytes to be lost from the body and pond water to ingress. The use of salt at 0.3% can help to prevent this and it and be taken up to 0.6% after 24 hours to maintain the fluid balance of the body (see table below).
Disease in perspective
Antibiotics are being used in place of good husbandry in many Koi ponds and this indicates that a close look is needed at the methods and practises in use to prevent disease outbreaks. Antibiotics are one of the most abused substances on the planet and we humans are sometimes to blame for taking them too soon when the immune system in a healthy person is made to fight infection. The Koi immune response is complex and few Koi will win the battle against bacteria if ulcers are left untreated. In reality, optimum pond conditions and good pond management are the very best deterrents against all Koi diseases. Bacteria outnumber viruses, fungi and the other pathogens that cause disease in living things and this makes them a formidable opponent in every branch of medicine. Bacteria utilise the resources available in whatever environment they are living in and it is this capacity that has made them so successful. They are one of the early forms of life on earth and, if the domination that bacteria exert is not overcome, they could be the last.
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