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Nitroimidazole – Metronidazole used for Hole in the Head/Lateral Line erosion (HITH/LLE) particularly in Cichlids is also one of the first line treatments for Clostridium difficile infections in people.
Ornamental fish can be captive bred or wild caught,
and on their way to the hobbyist are likely to pass through several transportation hubs, rather like any international traveller, disseminating infectious organisms around the world. This is exemplified by sporadic reports of hobbyists catching salmonellosis from fish. Salmonella are transitory inhabitants of the fish gut and in tracing the source of the infection it is often found
to be contaminated water from one of these “hubs”. Intriguingly a recent blog from UK government scientists ( ninos-waterborne-disease-emergence) argued that the last three significant El Niño events saw new variants of waterborne pathogens emerge in South America. Not only can dissemination be manmade but also probably naturally.
Clearly from the above there is potential for the ornamental fish hobby to impact the health of people for good or for bad. Morally and ethically as aquatic animal veterinarians we need to reduce the use of antibiotics and ensure we use them effectively. Routinely taking swabs for culture and sensitivity might be an option
but often getting good samples requires the sacrifice
of fish which is unacceptable to hobbyists. Taking
swabs from ulcers often grows A. hydrophila, however one of the causes of ulcer disease is A. salmonicida which is overgrown by A. hydrophila. Further, if samples are sent to laboratories with little fish experience then resistance can be amplified by incorrect use of media or interpretation of resistance incorrect. As such culture and sensitivity is not really helpful in many circumstances.
The question becomes can we treat infections
in ornamental fish without the use of antibiotic? Mycobacteriosis should not be treated due to the zoonotic implications and any associated fish in the tank should be kept isolated. Except for septicaemia and HITH/LLE there should be little call to use antibiotics and whenever possible they should be administered
by injection. This ensures correct dosage and minimal wastage of antibiotic. Using baths or prolonged immersion should be avoided due to the amount of antibiotic used to achieve the correct dose. In-feed antibiotics can often be pointless as ill fish do not eat, although using appetite stimulants such as garlic or aniseed can help. Fish less than 5cm in body length are difficult to inject and the injection site should always be massaged immediately afterwards or the antibiotic will leak out.
Many bacterial infections of ornamental fish can be treated and/or controlled whilst stressors such as poor water quality are improved. As example, ulcers
An Urban Experience
can be healed by cleaning with a topical antiseptic
such as povidone-iodine as fish skin will not seal the defect in the presence of bacteria, but can seal large deficits within 24 hours under the right conditions. In cold water fish increasing the water temperature will improve the function of the immune system and minimise scarring. Using supportive therapies such as vitamin C
or levamisole (both 10mg/l) will also improve immune function. The use of disinfectants such as Virkon Aquatic will control and decrease bacteria in the water column as will the use of salt in fresh water fish which will also decrease osmotic stress allowing more energy to fight the infection.
By learning a bit about ornamental fish and educating our clients then there will be minimal need to dispense antibiotics which is perhaps the biggest negative for One Health in ornamental fish. Then we can gain through reducing stress in our lives through watching fish in a well maintained tank, knowing that we are helping to protect the natural environment through the economic benefits to indigenous peoples around the world.
Further reading:
Watanabe, T., Aoki, T., Ogata, Y., Egusa, S., 1971. R factors related to fish culture. Ann. N.Y. Acad. Sci. 2001; 182, 383–410.
Lewbart G. Bacteria and ornamental fish. Semin Avian Exot Pet 2001;10: 48–56.
Cabello F. Heavy use of prophylactic antibiotics in aquaculture: a growing problem for human and animal health and for the environment. Method Enzymol 2006;8: 1137–44.
Smith P. Antimicrobial use in shrimp farming in Ecuador and emerging multi- resistance during the cholera epidemic of 1991: A re-examination of the data. Aquaculture. 2007;271(1-4):17.
Smith P. Antimicrobial resistance in aquaculture. Rev sci tech Off int Epiz. 2008;27(1):243–264
Garneau-Tsodikova S, Labby K. Mechanisms of resistance to aminoglycoside antibiotics: overview and perspectives. Medchemcomm 2015;7:11–27
Smith, Kronvall. Effect of incubation temperature and time on the precision of data generated by antibiotic disc diffusion assays. Journal of Fish Diseases 2015;38:629–36.
Martinez-Urtaza J, Trinanes J, Gonzalez-Escalona N, Baker-Austin C. Is El Niño a long-distance corridor for waterborne disease? Nature Microbiology 2016;1:16018.
Stentiford G, Sritunyalucksana K, Flegel T, Williams B, Withyachumnarnkul B, Itsathitphaisarn O, et al. New Paradigms to Help Solve the Global Aquaculture Disease Crisis. Plos Pathog 2017;13:e1006160.

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