By Dr. Noémie Hofman, DVM, CertAqV — WAVMA Certified Aquatic Veterinarian, Dubai
Fish are extraordinarily good at hiding illness. As prey animals, showing weakness in the wild is dangerous, so the instinct to appear normal is deeply embedded. By the time most fish owners notice something is wrong, the underlying condition has often been developing for days or weeks. This is one of the most important things to understand about fish health: what you see is almost never the whole picture.
As the only WAVMA Certified Aquatic Veterinarian in Dubai, I see ornamental fish patients from freshwater community tanks, marine reef setups, and high-value koi collections. The conditions I encounter most often are not mysterious or rare. They are the predictable consequences of specific husbandry issues, water quality problems, or infectious agents that flourish when fish are stressed. Understanding them makes early recognition possible, and early recognition saves lives.
This post covers the most common disease presentations I see in Dubai fish patients, what causes them, how to recognise the early signs, and what to do.
Important note: This article is for educational purposes and to help owners recognise when veterinary attention is needed. It is not a substitute for clinical examination and diagnosis. Many fish diseases look similar on the surface and require laboratory testing to confirm. If your fish is unwell, contact a qualified fish vet rather than starting treatment based on internet descriptions alone. Incorrect treatment can cause significant harm.
Why Dubai Is a Particularly Challenging Environment for Fish
Before covering specific diseases, it is worth understanding why fish health management in Dubai has some unique challenges compared to other regions.
Dubai’s ambient temperature is extreme for much of the year. Outdoor ponds, including koi ponds, are subject to water temperatures that can reach levels harmful to fish during summer months. Indoor aquariums rely on air conditioning to maintain appropriate temperatures, which means power fluctuations or equipment failure can cause rapid temperature swings. Temperature instability is one of the most consistent stressors that predisposes fish to infectious disease.
Dubai’s tap water chemistry also varies and requires careful management before use in aquariums. Chlorine and chloramine levels, pH, and hardness need to be adjusted depending on the species being kept. Owners who are unaware of this or who skip water preparation steps create chronic low-level stress in their fish that eventually manifests as disease.
Finally, ornamental fish in Dubai are imported from breeding facilities and wholesalers around the world. Import stress, transport, and the introduction of new fish to established systems are consistent triggers for disease outbreaks, particularly parasitic infections.
The Most Common Fish Diseases I See
1. Bacterial Infections
Bacterial disease is the single most common category of illness in ornamental fish. It presents in many ways including fin rot, ulceration, skin lesions, cloudy eyes, abdominal swelling also known as dropsy, and general lethargy. The bacteria responsible are often opportunistic, meaning they are present in most aquatic environments at low levels but only cause disease when fish are immunocompromised through stress, poor water quality, injury, or concurrent infection.
The most important clinical distinction in bacterial disease is between external and internal infection. External presentations such as fin rot and surface ulcers are often treatable with appropriate antibiotic therapy. Internal bacterial infections, particularly those causing abdominal swelling from fluid accumulation in the body cavity, carry a much more guarded prognosis and require prompt veterinary attention. What is sometimes called dropsy in fish is not a disease itself but a symptom of internal bacterial infection, internal mass growth or organ failure. By the time a fish shows the characteristic raised scale appearance associated with this condition, the prognosis is unfortunately often poor, which is why early recognition of less obvious signs matters so much.
Treatment requires identifying the causative bacteria and their antibiotic sensitivity profile. Treating with the wrong antibiotic or with over-the-counter treatments without knowing what you are treating is one of the most common reasons fish do not respond to attempted home treatment.
2. Parasitic Infections
Parasites are the second most common presentation and in Dubai they are frequently introduced through new fish purchases, live food, or contaminated equipment. The most clinically significant parasites in ornamental fish fall into several categories.
Ectoparasites affect the skin and gills and include white spot (Ichthyophthirius multifiliis in freshwater, Cryptocaryon irritans in marine), velvet disease (Oodinium), flukes (Gyrodactylus and Dactylogyrus species), and anchor worms. White spot is probably the most recognised fish disease among hobbyists, presenting as small white granules on the body and fins. What is less well understood is that the visible white spots are the reproductive stage of the parasite, not the feeding stage, which means treatment needs to be timed correctly to be effective.
Gill parasites are particularly dangerous because they cause respiratory distress that can become critical quickly. Fish with gill fluke infestations often show subtle signs initially, including increased breathing rate, flashing or rubbing against surfaces, and reduced activity. By the time obvious respiratory distress is apparent, significant gill damage may already have occurred.
Internal parasites including intestinal worms and systemic protozoal infections are less visible but equally damaging. Fish with internal parasite burdens often show gradual weight loss despite apparently normal appetite, changes in faecal appearance, and progressive lethargy. Diagnosis requires faecal examination or in some cases post-mortem analysis, which is why clinical examination by a qualified fish vet matters.
3. Fungal Infections
Fungal infections in fish most commonly present as white or grey cotton-wool-like growths on the skin, fins, or around the mouth. They are almost always secondary infections, meaning they colonise tissue that has already been damaged by a bacterial infection, physical injury, or parasite infestation. Treating the fungal growth without addressing the underlying cause leads to recurrence.
Egg fungus is a particular concern for fish breeders, where fungal colonisation of unfertilised eggs can spread to healthy eggs rapidly. Environmental management including water quality optimisation is as important as antifungal treatment in these cases.
4. Viral Diseases
Viral diseases in ornamental fish are less commonly diagnosed in general practice but represent some of the most serious conditions, particularly in koi collections. Koi Herpesvirus, or KHV, is a highly contagious and frequently fatal disease of koi and common carp with no effective treatment once clinical signs appear. Prevention through strict quarantine protocols for new fish is the only reliable protection.
Lymphocystis is a viral condition that produces cauliflower-like growths on the skin and fins. It is rarely fatal and often self-limiting in fish that are otherwise healthy, but it is frequently misidentified as a fungal or bacterial infection by owners attempting home treatment. Correct identification requires clinical examination.
5. Water Quality Related Disease
This is not a single disease but a category that accounts for a significant proportion of fish presentations I see. Chronic exposure to suboptimal water conditions causes cumulative physiological stress that eventually manifests as a clinical problem. The most common water quality issues causing disease in Dubai fish patients include:
- Elevated ammonia from overstocking, overfeeding, or inadequate filtration
- Nitrite toxicity from a cycling failure or new tank syndrome
- pH instability causing gill damage and osmoregulatory stress
- Incorrect temperature for the species kept, particularly during Dubai summers
- Chlorine or chloramine toxicity from untreated tap water
- Oxygen depletion, particularly in warmer water which holds less dissolved oxygen
Fish suffering from water quality problems often show non-specific signs including lethargy, reduced appetite, increased breathing rate, and hovering near the surface. These signs are easy to attribute to other causes, which is why water parameter testing is always the first step in any fish health assessment.
6. Nutritional Deficiencies
Ornamental fish fed a monotonous diet or poor quality commercial food over extended periods develop nutritional deficiencies that manifest in various ways including skeletal deformities, poor growth, colour loss, compromised immune function, and increased susceptibility to infection. This is particularly relevant for carnivorous species kept on vegetable-based diets, and for fish fed exclusively on one food type regardless of their natural dietary requirements.
Nutritional assessment is part of every aquatic consultation and dietary correction is often a component of the treatment plan even when the presenting complaint appears to be primarily infectious.
Early Warning Signs Every Fish Owner Should Know
The following signs should prompt you to contact a qualified fish vet rather than waiting to see if the fish improves:
- Any change in swimming behaviour including listing, spiral swimming, sinking, or inability to maintain position
- Loss of appetite lasting more than two to three days
- Visible lesions, ulcers, growths, or colour changes on the body or fins
- Rapid gill movement or breathing at the surface
- Clamped fins held close to the body
- Flashing, which means rubbing or scratching against tank surfaces
- Abdominal swelling or raised scales
- Eye changes including cloudiness, protrusion, or haemorrhage
- White, grey, or gold dust-like particles visible on the skin
- More than one fish in the same system showing signs simultaneously
The last point is particularly important. When multiple fish fall ill at the same time it almost always indicates an environmental cause or an infectious agent that is spreading through the system. Individual treatment of affected fish without addressing the underlying cause will not resolve the problem.
Why Self-Treatment Often Fails
Pet shop treatments and online advice lead many fish owners to attempt treatment before seeking veterinary advice. There are several reasons why this frequently does not work and sometimes makes things worse.
Most over-the-counter fish treatments are broad-spectrum products designed to address a possible cause rather than a confirmed one. Using an antiparasitic treatment on a bacterial infection, or an antifungal on a viral condition, does nothing for the underlying disease while stressing the fish and disrupting the beneficial bacterial populations in the filter that maintain water quality.
Many fish diseases share similar external presentations. White spots on a fish could be ich, velvet, lymphocystis, bacterial lesions, or physical damage depending on the species, the water conditions, and the history. Treating the wrong condition delays effective treatment and costs the fish time it may not have.
Antibiotic resistance is an increasing problem in aquatic medicine as it is in human and veterinary medicine generally. Using antibiotics without sensitivity testing contributes to resistance and may leave you with fewer treatment options if the correct antibiotic is needed later.
Getting the Right Diagnosis
As the only WAVMA Certified Aquatic Veterinarian in Dubai, Dr. Noémie Hofman provides clinical fish consultations that include a full history and environmental assessment, water quality testing, physical examination under sedation where indicated, skin scrapes, gill biopsies, and cytology, blood work, and bacterial culture with antibiotic sensitivity testing where appropriate.
An accurate diagnosis is the foundation of effective treatment. The difference between a fish that recovers and one that does not is very often the difference between treatment based on a confirmed diagnosis and treatment based on a guess.
If your fish is showing any of the signs described in this article, get in touch through the contact page.