18 Common Fish Diseases and Treatment Tips

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Common fish diseases encompass a range of ailments that can afflict aquatic species, posing significant challenges to aquaculturists and hobbyists alike. From bacterial and fungal infections to parasitic infestations, these diseases can have devastating effects on fish populations if left untreated.

Understanding the causes, symptoms, and preventive measures is essential for maintaining the health and well-being of both wild and captive fish. This introductory exploration delves into some of the most prevalent diseases affecting fish, shedding light on their impacts and offering insights into effective management strategies.

Common Fish Diseases

1. Anchor Worms

Anchor worms, misnamed for their appearance, are parasitic crustaceans, specifically Lernaea species, afflicting pond fish. Despite their name, they’re not worms. These parasites latch onto fish, embedding their heads into muscle tissue, often leading to irritation and susceptibility to fish diseases. Primarily targeting pond fish, they cause discomfort and potential health issues.

Symptoms of Anchor Worms

Anchor worms present with red, inflamed scales on fish, often accompanied by visible whitish-green thread-like parasites protruding from the body. Affected fish may exhibit rubbing against tank surfaces, along with signs of lethargy, ragged fins, and increased mucous production. Detection typically involves close observation for these distinct symptoms, indicating a potential infestation. Treatment should be prompt to alleviate discomfort and prevent further harm to the fish.

Treatment of Anchor Worms

Anchor worms, common among larger aquatic species, can be manually removed by gently pulling on the parasite’s body. After removal, applying topical antibiotic ointment aids in healing. Treatment involves anti-parasitic medications and regular water changes to eliminate any remaining eggs or larvae. Thorough tank cleaning is crucial. For smaller species, Hiraki USA Cyropro is effective without disrupting biological filtration, offering a targeted solution.

Common Fish Diseases

2. Bacterial Infections

Fish are susceptible to bacterial infections, often stemming from injuries. Aeromonas salmonicida is a prevalent bacterium causing such infections, leading to various fish diseases. Prompt recognition and treatment are crucial to prevent spread and save affected fish. Regular monitoring and maintaining clean aquatic environments can help mitigate the risk of bacterial outbreaks in fish populations.

Causes of bacterial infections

Poor water quality and inadequate nutrition often lead to bacterial infections in fish. These conditions induce stress, compromising their immune systems and facilitating the onset of infections. Maintaining optimal water conditions and providing a balanced diet are crucial in preventing such health issues and promoting fish wellbeing.

Signs of a bacterial infection

Common signs of a bacterial infection in fish include red spots, gill ulcers, swollen eyes, and abdominal swelling. Additional symptoms include rapid gill movement, skin discoloration, and ulcers. These indicators highlight the presence of a bacterial infection, necessitating prompt attention and appropriate treatment to mitigate potential harm to the fish population.

Treatment of bacterial infections

To address fish diseases such as bacterial infections in aquariums, veterinarians prescribe antibiotics tailored to the specific bacteria present. Over-the-counter medications like API’s Furan-2 or Triple Sulfa are available for hobbyists. Administer antibiotics in the water, while isolating affected livestock in a quarantine or hospital tank.

Before returning them to the main tank, rectify any tank issues and clean it thoroughly. Adjusting the tank population can help prevent future infections. Bacterial outbreaks often stem from poor water quality. Regular maintenance and monitoring are crucial for maintaining a healthy aquatic environment and preventing disease spread.

Read More: Eel fish farming

3. Constipation

Constipation in fish leads to illness if they cannot excrete waste. Prompt action is crucial to prevent complications. Regular monitoring of fish health and ensuring a suitable environment are essential for their well-being.

Causes of Constipation

Constipation in fish, primarily stemming from dietary issues or parasitic infections, can lead to discomfort and potential health complications.

Poor diet and parasite presence hinder fecal passage, necessitating measures to mitigate such issues. Additionally, proactive management strategies for fish diseases, including preventive measures against parasites, are crucial for ensuring fish gastrointestinal health and regular excretion.

Symptoms of Constipation

Constipated fish exhibit bloated abdomens, often leading to swim bladder disease and buoyancy problems. Symptoms include loss of appetite and abdominal bloating. Watch for these signs to detect constipation in your fish and take appropriate measures to prevent further complications.

Treatment of Constipation

One effective approach to alleviate constipation and address fish diseases is through dietary adjustments, such as boosting fiber intake and administering deworming medications. Additionally, adding Epsom salt to the tank can aid in relieving constipation.

API offers a readily available product for this purpose. Simply adding 1 to 3 teaspoons of Epsom salt per 5 gallons of water can facilitate muscle relaxation, easing the passage of stool. This dual strategy enhances nutrition while providing a gentle yet effective solution for constipation in aquatic environments.

4. CO2 Poisoning

Elevated CO2 levels exceeding 30 ppm pose a threat to aquatic life, particularly in CO2-injected planted tanks. Symptoms of CO2 poisoning include accelerated respiration, gasping at the water’s surface, abnormal swimming patterns, and lethargy among fish. These signs indicate distress and potential harm to aquatic organisms, including susceptibility to fish diseases.

Monitoring CO2 levels diligently is crucial to maintaining a healthy aquatic environment, as excessive CO2 can disrupt the delicate balance necessary for aquatic life to thrive. Swift action, such as adjusting CO2 injection rates or improving aeration, is necessary to mitigate risks and safeguard the well-being of aquarium inhabitants.

Causes of CO2 Poisoning

CO2 poisoning can result from a malfunctioning CO2 reactor or inadequate CO2 absorption by plants due to faulty lighting. Insufficient CO2 removal can lead to dangerous levels in enclosed environments, which may exacerbate fish diseases. Monitoring reactor functionality and ensuring proper plant health are crucial to prevent this potentially harmful situation.

Treatment for CO2 Poisoning

To effectively manage CO2 poisoning and prevent potential fish diseases, employ an air stone to agitate water surfaces, facilitating carbon dioxide dispersion. This process aids in restoring a healthier balance. Additionally, fine-tune CO2 injection rates within the tank to regulate levels.

Balancing agitation and injection ensures optimal conditions for aquatic inhabitants, mitigating the risks associated with CO2 buildup.

5. Flukes

Flukes, external parasites as per Cuttlebrook Koi Farm, predominantly target fish gills, with Dactylogyrus and Gyrodactylus being the primary types. These parasites can manifest as either body or gill flukes. Fish diseases caused by these parasites can lead to significant health issues, including respiratory distress and compromised immune function.

The causes of their infestation vary, potentially stemming from poor water quality, introduction via new fish, or contaminated equipment. Such infestations can result in significant health issues for fish, including respiratory distress and compromised immune function.

Vigilance in maintaining water quality and careful quarantine procedures for new additions are crucial preventive measures against fluke infestations and other fish diseases in aquatic environments.

Causes of Flukes

Flukes, common in aquariums, often enter through infected fish. These parasitic flatworms pose a threat to aquatic health. Vigilance in identifying and treating fluke infestations is crucial for maintaining a thriving aquarium ecosystem.

Symptoms of Flukes

Flukes latch onto fish gills and skin, causing damage and potential bacterial infection, leading to various fish diseases. Symptoms encompass altered slime coat and gill deterioration, indicating infestation. Vigilance in observing these signs is crucial for timely intervention and safeguarding fish health against fluke-related complications.

Treatment of Flukes

Praziquantel is the primary treatment for flukes in fish. Utilize antifungal remedies, seek veterinary advice, or consult experienced hobbyists for effective management of fish diseases. Post-treatment, administer antibiotics to address any resulting wounds. Effective management of flukes, as well as other fish diseases, involves a multi-step approach for optimal health and recovery in aquatic environments.

6. Clamped Fins

Clamped Fins is a condition in fish where their fins are tightly pressed against their body, indicating stress or illness. This behavior is often a sign of discomfort or poor health, requiring attention and potentially medical intervention to address underlying issues and ensure the fish’s well-being.

Causes of Clamped fins

When fish encounter poor water conditions, external parasites, or fish diseases, they typically retract their fins close to their body. This behavior serves as a defensive response, indicating distress or discomfort. Such adjustments help fish cope with environmental challenges, maintaining their health and well-being in aquatic habitats.

Symptoms of Clamped Fin

Clamped fin in fish manifests as lethargy, with fins held close to the body during swimming. White patches and spinal deformities might also appear. These symptoms indicate stress or illness, requiring prompt attention and potential intervention to restore the fish’s health and well-being.

Treatment of Clamped Fins

To address fish diseases like clamped fins, assess water quality and inspect for external parasites. Remove parasites manually, isolate new fish, and employ UV sterilization to hinder future spread. Regular monitoring and maintenance are vital for a healthy aquatic environment, ensuring the well-being of your aquatic companions.

7. Dropsy

Dropsy refers to fish exhibiting swelling, often due to kidney disease. The condition results in fluid retention, causing the fish’s body to bloat. It’s a common ailment in aquariums, requiring prompt treatment to alleviate discomfort and prevent further complications in affected fish.

Symptoms of Dropsy

Dropsy often manifests through visible signs like mild to severe abdominal swelling, sometimes causing the scales to protrude, resembling a pinecone. Affected fish may also experience scale loss and exophthalmia, characterized by bulging eyes. These symptoms serve as key indicators of dropsy, a condition commonly observed in aquatic environments, necessitating prompt attention and intervention to mitigate its effects on the fish’s health and well-being. Furthermore, understanding common fish diseases, including dropsy, is crucial for maintaining optimal aquatic ecosystems.

Cause of Dropsy

Fish kidney problems can stem from various factors like stress and Polycystic Kidney Disease. Stressors such as poor water conditions or handling can impact kidney health. Polycystic Kidney Disease, a genetic disorder, manifests as cyst formation within the kidneys, further exacerbating fish health issues.

Treatment for Dropsy

To tackle Dropsy, start by isolating the affected animal in a quarantine tank to reduce stress and pinpoint potential issues in the main tank like poor water quality or overcrowding. Consult a vet promptly, although finding one experienced with fish might be challenging.

Local aquarium stores could offer recommendations. Alternatively, if veterinary guidance is not immediately available, follow Lori Hartland’s method, combining Kanaplex, Metroplex, and Epsom Salt treatment, as detailed in her video. Emphasize the importance of veterinary guidance, even if it means a phone consultation.

Additionally, educate yourself about common fish diseases, including fish diseases such as fish diseases, to better understand potential causes and treatment options. Avoid relying solely on salt baths, as they may not yield optimal results. Lori’s approach and the use of wheelchairs have proven effective in managing Dropsy.

8. Freshwater Ich

Ichthyobodo, a protozoan parasite, infects stressed fish, causing Ichthyobodiasis. Manifesting in skin and gill lesions, it induces respiratory distress, leading to mortality. Effective treatment involves improving water quality and using medications like formalin or copper sulfate. Vigilance in stress management is crucial for preventing outbreaks.

Symptoms of Ich

Ich, or Ichthyophthirius multifiliis, infests fish gills and skin, manifesting as a grey hue on their skin. Infected fish display lethargy, weakness, and loss of appetite, often lingering near the water’s surface, gasping for air, or rubbing against tank surfaces. White feces, scratching behavior, and rapid gill movements are also common indicators. Fish diseases like Ichthyophthirius multifiliis, commonly known as Ich, can compromise fish health, demanding swift treatment to prevent its spread and alleviate fish distress.

Cause of Ich

Stress, stemming from factors like water quality, overcrowding, or illness, including fish diseases, is the primary trigger for Ich in fish. Heightened stress weakens their immune defenses, enabling the proliferation of the Ich parasite. This protozoan infestation manifests as white spots on the fish’s body. Maintaining optimal water conditions and minimizing stressors are essential for preventing Ich outbreaks and safeguarding fish health.

Treatment for Ich

If your fish exhibits signs of Ich or other fish diseases, consult a vet or aquatic specialist for proper treatment guidance. Common remedies include aquarium salt, potassium permanganate, or copper sulfate, but precise dosing is crucial.

Overmedication can harm fish. Ich-X is Mark’s preferred freshwater solution, but monitor for secondary infections, which can be more lethal than Ich alone. Copper-based treatments are effective for severe cases. Regular water changes help maintain water quality.

However, reserve copper treatments for more severe illnesses. Seeking expert advice ensures the well-being of your aquatic pets, preventing harm from incorrect medication or untreated infections.

9. Freshwater Velvet (Gold Dust Disease)

Velvet disease, along with other fish diseases, poses a lethal threat to aquariums, swiftly decimating fish populations. Its rapid spread can devastate entire tanks, necessitating immediate intervention to prevent widespread loss. Vigilance and prompt treatment are crucial to mitigate its destructive impact on aquatic ecosystems.

Symptoms of Velvet

Fish afflicted with velvet, one of the common fish diseases, exhibit abnormal behaviors such as incessant scratching against tank surfaces to rid themselves of parasites. This condition manifests through lethargy, reduced appetite, weight loss, and fin clamping. Additionally, rapid or labored breathing and a yellowish to rust-colored dust on their skin signify infection.

Severe cases may involve skin peeling and cloudy eyes. Treatment typically involves medication to eradicate parasites and enhance fish immunity. Prompt action is crucial to prevent further deterioration and potential fatalities among affected fish.

Causes of Velvet

Velvet, caused by parasites Oödinium pillularis or Oödinium limneticum, manifests in stressed, sick, or poorly cared-for aquarium fish. Common in aquariums, it becomes problematic during stress, transportation, sudden temperature changes, or poor water quality. Prevention and prompt treatment are crucial to maintaining fish health and aquarium balance.

Treatment of Velvet

To address fish diseases like velvet, follow these steps: slightly raise water temperature, dim aquarium lights, treat with copper sulfate like Copper Power or SeaChem Cupramine for 10 days in a quarantine tank (never in display tank). Prevention includes quarantining new fish, maintaining a proper diet, and ensuring water quality.

For saltwater tanks, refer to Mark’s Marine Velvet article. Implement biosecurity measures such as quarantine for new additions for future prevention. These practices help maintain a healthy aquatic environment, reducing the risk of velvet outbreaks and promoting the well-being of your fish.

10. Fungus

In freshwater aquariums, common fungal infections include Saprolegnia and Ichthyophonus hoferi, which can lead to fish diseases. Saprolegnia is a filamentous fungus, while Ichthyophonus hoferi is a unicellular parasite. Both infections require proper management to maintain the well-being of aquatic organisms. Additionally, vigilance against fish diseases such as fungal infections is essential for ensuring the health of the aquarium ecosystem.

Symptoms of Fungal Infections

Fungal infections in fish can harm internal organs, evident through grey cotton-like growths on skin, gills, fins, and near eyes. These infections signify potential organ damage, requiring prompt treatment to safeguard fish health. Vigilance and swift intervention are crucial to prevent further complications and ensure aquatic well-being.

Causes of Fungal Infections

Fungal infections stem from poor water quality and organic debris in tanks. Unclean water harbors fungal pathogens, endangering aquatic life. Proper maintenance, filtration, and water testing mitigate risks. Prevention includes regular cleaning and minimizing organic buildup to sustain a healthy aquatic environment and prevent fungal outbreaks.

Treatment of Fungal Infections

To treat fish diseases, including fungal infections, in your aquarium, begin by thoroughly cleaning the tank and removing any external pathogens from your fish’s skin. Add potassium permanganate to the water to disinfect.

Consider using API Fungus Cure as a topical treatment after cleaning. Disinfect aquarium equipment to prevent further spread. Increasing water temperature to 82 degrees Fahrenheit can help inhibit fungal growth, as they thrive in colder conditions.

By following these steps, you can effectively combat fungal infections and other fish diseases in your aquarium, ensuring the health and well-being of your aquatic pets.

11. Gill Mites

Gill mites, prevalent in aquariums, are parasitic organisms that cling to fish skin, nourishing themselves by consuming their blood. These tiny pests pose a threat to fish health, often leading to discomfort and potential complications if left untreated, necessitating diligent monitoring and appropriate management in aquarium environments.

Additionally, understanding common fish diseases is crucial for maintaining the overall health and well-being of aquarium inhabitants.

Symptoms of Gill Mites

Gill mites hinder gill closure in fish, impairing their respiratory function. Affected fish exhibit surface gasping, abnormal swimming patterns, and red streaks on their bodies. These symptoms signal compromised gill health, necessitating prompt intervention to safeguard the fish’s well-being and prevent further deterioration of their condition.

Causes of Gill Mites

Mites infiltrate tanks via new livestock, emphasizing the need for quarantine. Precautionary isolation before introducing new additions to an aquarium helps prevent mite transmission and other fish diseases. This practice safeguards tank inhabitants from potential infestations and maintains aquatic ecosystem balance. Quarantine is a vital step in ensuring aquarium health, stability, and protecting against fish diseases.

Treatment of Gill Mites

To combat gill mites and other fish diseases, employ sterazin and octozin medications, with a repeat treatment after 5 days to eradicate hatched mites. Disregard advice on immunostimulants and lighting adjustments for fish recovery as unverified. Refer to reliable articles on fish immunostimulants for accurate information, as they remain insufficiently researched.

12. Hole In The Head

Hole in the head disease, or Hexamita, manifests as small indentations on a fish’s head or lateral line. It’s a condition often observed in aquatic environments, indicating infection, which is just one of many fish diseases. Prompt diagnosis and treatment are crucial to mitigate its effects and maintain the health of affected fish populations in aquariums or natural habitats.

Symptoms of Hole in the Head

Hole in the Head disease in fish manifests as small skin indentations progressing to severe holes, leading to appetite loss. It causes fecal changes and parasitic cysts. Symptoms include skin depressions, impacting fish health and behavior, highlighting the importance of prompt diagnosis and treatment in aquatic environments.

Causes of Hole in the Head

Hole in the head, prevalent in Discus fish, stems from Hexamita protozoan infection and mineral deficiency, often triggered by RODI water or excessive activated carbon. This condition manifests as lesions on the fish’s head. Proper water maintenance and diet adjustments are crucial for prevention and treatment.

Treatment of Hole in the Head

The recommended treatment involves isolating the affected fish in a quarantine tank and administering Metronidazole or API General Cure. Medicated food, prepared with focus and either General Cure or Metro, can also be utilized for treatment. This method helps effectively address the condition while minimizing risks to other aquatic inhabitants.

13. Hemorrhagic septicemia

Hemorrhagic septicemia, caused by Piscine novirhabdovirus, is a fatal viral infection in fish. It leads to severe hemorrhaging and systemic damage, posing a significant threat to aquatic populations. Swift diagnosis and containment are crucial to prevent widespread mortality and preserve the health of aquatic ecosystems.

Symptoms of Hemorrhagic septicemia

This disease induces internal bleeding in fish, manifesting as small red dots on the skin, alongside symptoms like pale gills, dark-colored body, fluid accumulation, and bulging eyes. Livestock may also exhibit hemorrhages and sudden death. Early detection and treatment are crucial to prevent extensive damage and mortality.

Treatment of Hemorrhagic septicemia

Effective treatment for the disease in fish remains elusive. Most afflicted fish succumb to the infection despite efforts. Remedial actions include tank cleaning and slight water temperature elevation. Antibiotics like API Triple Sulfa, Kanamycin, and Thomas Labs Fish Mox may be administered. Avoid carbon filters during medication as they remove the treatment along with impurities, hindering its efficacy.

14. Lice

Fish can contract external parasites like lice, which latch onto their skin and feed on blood, leading to anemia. These small pests pose a threat to fish health, necessitating vigilant monitoring and appropriate treatment to safeguard aquatic populations from potential harm and disease outbreaks.

Symptoms of Lice

Fish with lice exhibit clear discs near their bodies, pale complexion from blood loss, and may rub against tank surfaces, causing external wounds. Additional symptoms include isolation and skin ulcers. Infestation prompts fish to attempt self-removal, leading to distressing behaviors and compromised health. Vigilance and intervention are crucial for their well-being.

Treatment of Lice

The optimal lice treatment involves physically removing parasites from the fish’s skin, supplemented with topical antibiotic ointment for wounds. Diflubenzuron (Dimilin-X) is a recommended over-the-counter medication for effective parasite elimination. Implementing quarantine measures can prevent future infections, ensuring fish health and well-being.

15. Pop-Eye

Pop-eye, a condition caused by bacterial infection, results in one or both eyes protruding from their sockets. This abnormality, typically affecting fish and sometimes birds, is characterized by the eye’s displacement due to swelling and pressure buildup, leading to a distinctive bulging appearance.


Exophthalmia, or bulging eyes, is a distinctive sign of this easily diagnosable condition. Accompanied by behavioral shifts such as appetite loss, it presents a clear clinical picture. Early detection of protruding eyes and associated changes in behavior facilitates prompt intervention and management of the condition.


Pop-Eye, typically caused by bacterial infection or vitamin A deficiency, can also stem from issues like ocular masses or water quality. Symptoms include protrusion of the eye(s). Treatment involves addressing underlying causes and may include antibiotics, dietary adjustments, or improving aquatic habitat conditions for affected aquatic organisms.


Pop-eye, a common fish ailment, often responds to tetracyclines, available from local veterinarians. Regular tank maintenance and water quality checks are crucial. If veterinary access is limited, over-the-counter options like SeaChem SulfaPlex may be considered. Ensure thorough cleaning of the tank for optimal recovery and fish health.

16. Swim Bladder Infection

The swim bladder, an essential organ in fish, regulates buoyancy by storing oxygen and gases. Dysfunction leads to depth control issues. Maintaining proper function is crucial for fish to navigate their aquatic environment effectively, ensuring they stay at desired depths without difficulty.


Swim bladder disease manifests through fish struggling to maintain balance, often tilting or floating awkwardly. They might linger near the surface or bottom of the tank, exhibit erratic swimming patterns, and lose interest in food.

These symptoms signal potential swim bladder issues, requiring prompt attention to ensure the fish’s well-being and proper aquatic environment.


Poor water quality and stress often trigger buoyancy issues in fish. This condition frequently affects newly acquired specimens, especially those transported improperly, like imports or wild-caught species.

If you observe your fish struggling with buoyancy, promptly assess tank water quality as it’s likely the root cause. Maintaining optimal water conditions is crucial for preventing and managing this ailment.


If your fish shows signs of swim bladder disease, consulting an aquatic vet is paramount. They can perform venting to release trapped air in the swim bladder and advise on water quality testing and regular 10% water changes. Hand-feeding may be necessary for fish struggling to maintain balance or staying at the tank’s bottom, ensuring proper nutrition.

Some hobbyists have devised harnesses to support fish, particularly effective for fancy goldfish. Mark Kennedy’s video provides a comprehensive guide on crafting such harnesses. Seeking professional guidance and exploring innovative solutions can enhance the well-being and longevity of your aquatic companions afflicted with swim bladder issues.

17. Tail and Fin Rot

Causes of Tail and Fin Rot

Fin rot, typically stemming from poor water quality or injury, manifests as the decay of fish fins. Inadequate cleanliness fosters infections in wounds, accelerating deterioration. Unclean water exacerbates the rotting process.

Effective aquarium maintenance and swift treatment of injuries are crucial in preventing and managing this condition for aquatic organisms’ health.

Signs of Tail and Fin Rot

Fish may exhibit signs of deteriorating health such as frayed and torn fins, ragged tails, and skin nodules, indicating fin erosion and potential infection. These symptoms suggest environmental stressors or disease, warranting prompt attention to ensure the fish’s well-being and prevent further deterioration of their condition.

Treatment of Tail and Fin Rot

To treat infections in aquariums, options include medications like SeaChem KanaPlex and API Fin and Body Cure, along with Methylene Blue from Kordon. Administering Methylene Blue at a rate of 1 drop per 2 gallons of water is recommended.

Additionally, conduct a 50% water change every other day for a week when using Methylene Blue. These treatments help address various infections in fish tanks effectively, ensuring the health and well-being of aquatic inhabitants.

18. Mouth Rot

Mouth rot, triggered by Flavobacterium bacteria, manifests as a fungal infection in reptiles, particularly prevalent in snakes and lizards. It leads to oral lesions, inflammation, and potentially systemic infection, compromising the reptile’s health. Timely veterinary intervention and proper husbandry practices are crucial for treatment and prevention.

Signs of Mouth Rot

Check for discoloration and white patches near the mouth; indicative of mouth rot. Recognizable by a cotton-like texture around the mouth. Untreated, it progresses to rotting skin. Early detection crucial for effective treatment and fish health.

Causes of Mouth Rot

Poor water conditions and stress compromise fish immunity, making them susceptible to fungal infections. Inadequate maintenance fosters an environment conducive to fungus growth. Improved water quality and reducing stressors can mitigate this issue, ensuring healthier aquatic habitats for fish to thrive in.

Treatment of Mouth Rot

Several antifungal options are available at aquarium stores to address fish health issues, including SeaChem KanaPlex, Thomas Labs Fish Min, and API Fin and Body Cure. Identifying stressors and maintaining water quality are essential for effective treatment.

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