Keeping fish without antibiotics

Nov 7 / Shane Willis
The use of antibiotics as treatments in our industry is commonplace and is an essential tool for fish health management. However, there is a growing concern by governments around the world for the incorrect use of antibiotics. The main concerns are the indiscriminate use of antibiotics leading to the development of resistant strains of bacteria and the 'masking' effect of antibiotics. The use of an antibiotic covers an underlying problem, such as a carrier state for a virus. These issues will see more regulation in antibiotics in our industry, and some governments are already making these changes. 
The Australian government has already made changes to the use of antibiotics in ornamental fish quarantine operations that have forced the Australian industry to look at alternatives to antibiotic use. This article looks at some of the issues of antibiotic 'abuse' and approaches we used to adapt to the quarantine of fish without antibiotics.

Bacterial resistance

The problem of bacteria developing resistance to antibiotics is not new, and there have been many documented cases of this in human medicine. In the case of human medicine, it is thought that the over-prescribing of antibiotics for ailments does not necessarily need antibiotics (i.e., viral infections such as colds). We have a similar problem in our industry where antibiotics are often used without any supervision by vets on an ad hoc basis with no proper diagnosis of what bacteria, if any, is causing the problem – without this diagnosis, it can be challenging to ensure the correct antibiotic is being used. Therefore many operators use a 'shotgun' approach to the treatment of 'bacterial' infections, using minimal diagnostic effort and simply applying different treatments until either the fish stop dying or the fish are all dead. 

This treatment regime is an ideal breeding ground for resistant strains to develop, and we see an increasing level in our industry. Several papers have reported the high prevalence of antibiotic-resistant bacteria isolated from ornamental fish and their transport water. Resistant strains of Columnaris, Vibrio, and Aeromonas are becoming more common and extremely difficult to deal with. While this makes bacterial infections more difficult to treat in fish, the other primary concern is worker safety with zoonotic infections (disease transferred from animals/fish to humans). There are many reports of zoonotic infections leading to significant disease in workers, which have resulted in amputations, and there is a documented case of the death of a fish worker from a resistant strain of Vibrio contracted from ornamental fish. There are also reports of workers on farms developing sores or ulcers on the arms and legs that take a long time to heal. Tests have revealed in some cases that these 'fish farmers sores' have resistant strains of bacteria present, and there are even reports about significant changes to the gastrointestinal bacteria population structure in workers exposed to antibiotics. While the number of these reports is still relatively low, it does point to a need to be more careful in the use of antibiotics in our industry.

Regulatory changes in Australia

The other major issue of the use of antibiotics is that the 'masking' has led to changes in regulations regarding the use of antibiotics in Australian quarantine stations, with the Australian Quarantine and Inspection Service (AQIS) effectively banning the use of antibiotics while fish are in quarantine. The regulations, formalized in May 2008, require importers to submit an application to AQIS for approval of the use of an antibiotic before using it. The application will only be approved where:

  • The use is for the treatment of fish with clinical signs of disease, i.e., No prophylactic use is permitted
  • A professional diagnosis by an AQIS approved laboratory where the disease organism is identified is given
  • The disease is endemic to Australia – any batch of fish found to have an 'exotic' disease are destroyed
  • The antibacterial is registered for use in ornamental fish or is prescribed by a veterinarian

As well as these conditions, after the treatment, the fish must undergo an extension to the quarantine period of:

  • Goldfish – 36 days
  • Gouramis and Cichlids – 28 days
  • Other freshwater species – 21 days
  • Marine fish – 7 days

    So, as you can see from these onerous regulations, we can effectively use antibiotics in our quarantine area and rely on other methods to address bacterial issues. When these regulations were implemented, the Australian industry was apprehensive about these new regulations' negative impact and expected the worst with high mortalities and poor quality fish coming through quarantine. However, the industry had no choice but to adapt to the new regulations, which has been done, and as it turns out, with relatively minimal impact with minimal increases to fish losses in quarantine.


So what are the alternatives?

Antibiotics are the best course of treatment when dealing with bacterial infections, and unfortunately, there is no magic bullet to replace them. Before discussing the alternatives, the leading causes of bacterial infections are worth noting. The following list, while not exhaustive, covers some of the major causes of bacterial infections:

  • Chronic low-level irritation due to poor water quality, including:
  • High levels of suspended solids (5 to 10-micron size)
  • Extreme pH
  • High ammonia and nitrites
  • Other water quality parameters outside normal tolerances of the species
  • Overstocking of fish, poor handling
  • Transport stress – this stress increases exponentially with time in transit
  • Poor hygiene and cross-contamination with diseased fish
  • Presence of parasites and other disease organisms
  • Poor nutrition

These causes have all been identified as issues contributing to 'Biosecurity' (refer to the recent OFI book 'Biosecurity in the ornamental Aquatic Industry') and factors vital to the success of holding fish in a healthy state. Knowing that these are the leading causes of bacterial problems, our approach is a combination of alternative measures based around:

  1. Quality of supply – you cannot afford to buy second-grade fish.
  2. Improved husbandry – good old-fashioned fish keeping, making sure water quality, nutrition, commo others are correct
  3. Use of disinfectant type chemicals for topical bacterial infections and to prevent the spread of disease
  4. Use of plant-based extracts for 'treating' fish or enhancing the immune system

Quality of Supply 

There is an expression that "you cannot make a silk purse from a sow's ear," which is very accurate when dealing with ornamental fish. If the quality of fish sent to the importer is poor, it is challenging to have successful quarantine with minimal losses, and this means that selecting the suppliers you deal with becomes very important and the price paid. The cheapest fish are not always the most economical fish – there is no point buying a cheaper priced fish if it is going to be of poor health and losing fish because you cannot use an antibiotic – it ends up costing more in the long run.  

Therefore, farmers and collectors need to ensure the fish they supply are in good health and have reasonable biosecurity measures to ensure that the fish are held in a healthy state at their facility. Increasing concerns about the spread of disease with ornamental fish and changes to import legislation by importer countries such as Australia will lead to increasing pressures on producers worldwide to be 'Biosecure,' and I believe this is the biggest challenge to the future of our industry. 

The other important thing to note about supply is having good communication between exporters and importers. Communication needs to be a two-way street with a discussion about problems and possible solutions going both ways. I spend much time talking to suppliers about issues in each shipment, visiting our suppliers, and offering advice on various factors, including water quality and disease control. I am also constantly asking questions about how the fish are farmed and held – information on water quality and nutrition is always essential to better match our holding conditions to what the fish have been grown in by the farmer. Sometimes the simple ability to exchange information can go a long way to solving quality issues.

Quality of Supply 

My personal view is that antibiotics are often used as a 'crutch' to make up for lax or inadequate husbandry practices such as poor water quality, increased stocking densities, and other factors that stress the fish that means that they need to manage their fish in ways that minimize stress (good water quality, minimal handling, good nutrition, adequate stocking density, fish health management program). Nutrition is likely to be an area that can be easily improved - Vitamin C and B complex are vital to the immune system and are easily incorporated into the diet. Research in Singapore also suggested that even adding vitamin C to water can improve the survival of ornamentals after transport and help reduce stress when receiving new shipments. Good hygiene practices are also essential to help prevent the spread of disease in a facility, even sorting/culling of poor quality sick fish can help prevent disease spreading. Our experiences here certainly support this, and paying more attention to correct husbandry practices can go a long way towards preventing problems with bacterial infections.
Therefore, farmers and collectors need to ensure the fish they supply are in good health and have reasonable biosecurity measures to ensure that the fish are held in a healthy state at their facility. Increasing concerns about the spread of disease with ornamental fish and changes to import legislation by importer countries such as Australia will lead to increasing pressures on producers worldwide to be 'Biosecure,' and I believe this is the biggest challenge to the future of our industry. 
The other important thing to note about supply is having good communication between exporters and importers. Communication needs to be a two-way street with a discussion about problems and possible solutions going both ways. I spend much time talking to suppliers about issues in each shipment, visiting our suppliers, and offering advice on various factors, including water quality and disease control. I am also constantly asking questions about how the fish are farmed and held – information on water quality and nutrition is always essential to better match our holding conditions to what the fish have been grown in by the farmer. Sometimes the simple ability to exchange information can go a long way to solving quality issues.

Use of disinfectants

There is a range of disinfectants that can be used for 'treating' external bacterial infections and include chemicals such as: 

  • Potassium permanganate
  • Chloramine-T 
  • Benzalkonium chloride
  • Malachite green 
  • Acriflavine
  • Hydrogen peroxide


Salt can also be used and has significant health benefits for the fish and acts as a disinfectant; however, these chemicals can be used to treat topical infections and control the spread of bacteria between fish/batches. Their use for treating systemic infections is minimal. 

Plant Extracts and Immunostimulants

The use of plant extract-based medications is an area that potentially holds great promise for new treatments that can be applied to our industry. Plant-based extracts for treating fish dating to ancient China are not new in the industry. A great example of a commercial product is Melafix, produced by Aquarium Pharmaceuticals in the USA, which is based on Tea Tree oil and can be used to treat topical bacterial infections in fish. This product also has the added benefit that it can reduce inflammation in affected areas and aid the recovery of the fish. Another plant well known for its curative powers is Ketappa or Indian Almond tree. The leaves of this tree are used throughout Asia to condition fish water and prevent bacterial infections with success. Even peat extract or blackwater is thought to have some curative and preventative powers.
Research is going on throughout the world into the use of plant-based extracts for use in fish. Recently the World Aquaculture Society Asia-Pacific Conference in Malaysia, where many presentations were given on various plant extracts for use in food fish species such as shrimps, tilapia, and marine fish to improve growth and survival. The plant extracts play two leading roles in promoting growth and survival. The first is to stimulate or enhance the fish's immune system, so it is better armed to fight off any infection, and two, the extracts are 'toxic' in some way to the diseases they act. As these 'extracts' are often based on a complex of different chemical compounds, they can often be more effective than traditional treatments and can produce both. While research into this area is relatively new, it does hold great promise as a possible replacement for traditional antibiotic treatments. Most research in this area tends to be from Asia and is often based on Traditional Chinese Medicine principles. One such product currently being commercialized is a Singapore-based product, 'G100' has shown promise in improving health and survival among several species.
The other benefit of plant extracts is a potential reduction in the development of bacterial resistance. Research from Israel suggests that bacteria may not develop resistance to these extracts in the same way they do to antibiotics – again, this is most likely due to the 'complex' of chemicals found in these plant-based extracts compared with specific chemicals, as is generally the case in antibiotics. Replacing antibiotic use with these extracts, therefore, can reduce the problems of worker safety previously highlighted.

Conclusion

Genuine issues surround the indiscriminate use of antibiotics leading to resistant strains of bacteria. These can cause significant economic losses to operators and lead to potential health risks for workers. Governments are also becoming more aware of the spread of disease via ornamental fish and the potential for antibiotics to mask carrier states in fish which can aid the spread of disease. While antibiotics have an important role in fish health management, the importance of good fish-keeping practices and biosecure measures should not be overlooked. Experience from Australia shows that fish can be kept successfully without antibiotics to some degree by 'going back to basics, and further improvements will likely come from increasing research into the use of plant extracts as treatments in all forms of aquaculture.

Useful references

Abutbul, S., et al., 2005. Screening of desert plants for use against bacterial pathogens in fish. Israeli Journal of Aquaculture. 57(2), p 71-80.

Dügenci, s., et al., 2003. Some medicinal plants are immunostimulants for fish. Journal of

Ethnopharmacology. 88, p 99–106.

Verner-Jefferys. D., 2009. High prevalence of Multidrug-tolerant bacteria and associated antimicrobial resistance genes isolated from ornamental fish and their carriage water.
Plus One. December 2009 Volume 4(12)

Zilberg, D., 2010. Dried leaves of Rosmarinus officinalis as a treatment for streptococcus in tilapia. Journal of Fish Diseases