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sick goldfish

Tropical Fish Diseases – Symptoms & Treatments

Are your fish healthy and active all the time? We hope so, but unfortunately, sometimes they do get sick, so it is better to be prepared now, rather than be sorry later.

In this tropical fish diseases and treatment guide we’ll help you identify the possible signs of danger and help you find the most suitable treatment for your tropical fish.

sick goldfish

The earliest sign that I get, that all is not well in my aquarium, is when the fish start to behave abnormally. Either they become overactive, swimming around in bursts, rubbing themselves with the rocks and stones or getting very quiet, almost lifeless. But soon enough there are visible signs on their bodies, some discoloration, deformation or protrusion on the skin.

These symptoms help me identify the disease they may be carrying and once I am sure, I can apply the proper treatment for it. I am listing here some common tropical fish diseases that may afflict your fish, their symptoms, causes, and possible cures.

This is a guide to tropical fish diseases and is a general guide to help you identify their illness so you can apply the correct treatment.

If in doubt, get a second opinion before starting treatment.

Here’s a list of the most common tropical fish diseases

Swim Bladder Disease


You will notice that the belly of the fish is swollen and its spine will not be straight but bent. Its swimming will be erratic and not able to swim straight but in circles. You may find it floating with its tail higher than the head and sometimes upside down. It will float up to the top of the tank and will not be able to go to the bottom of the tank.


This is not a specific disease but can result due to many diseases. As the name implies these diseases affects the swimming bladder of the fish and therefore it cannot maintain its depth in the tank. The cause of this disease may be a bacterial or parasitic infection or can be due to some physical damage to it. Some fish are born with this defect so they don’t survive for long with it.


Start by raising the temperature of your aquarium to 80 degrees Fahrenheit. Sometimes, lowering the water level can help by making it easier for the fish to swim around. Also reducing the water flow within the tank will help and cause them less hard and stress which will not aid their treatment.

Then you can start the treatment which may seem a little unusual to a novice. Don’t feed your fish for 3 days. Then on day 4 feed your fish skinned peas. Frozen peas are easier to use and seem to work best. All you have to do is microwave or boil them to soften them enough to remove the outer skin. Once you have removed the outer skin, you can feed the peas to your fish. The pea will help to clear out your fish’s system and their symptoms will start to improve.

Body Flukes


Your fish will be irritated and will scratch itself with objects in the aquarium when it is inflicted with body flukes. Its body and gills will be covered in a layer of mucous. Inflammation on the skin can be spotted by its reddening. Some gills and fins might be damaged and seem to be chewed away.

body flukes
Image Credits @aquaticsworld.co.uk


This disease is caused by flukes which are flatworms about 1mm long. These are normally present in the aquarium but do not affect your fish if the aquarium is clean. However, if the water quality deteriorates, there is overcrowding and the fish are under stress due to any reason then they get infected. Once an outbreak of flukes occurs it spreads rapidly and you must control it quickly to avoid serious losses.


Isolate the fish and treat with Body Fluke treatment such as Hikari Liquid PraziPro. Always follow guidelines given on the treatment bottle and isolate the fish before treating. Symptoms should start to reduce within 4-5 days. Body flukes will spread quickly throughout your aquarium so quick treatment is vital and isolation at all  possible is the best option.

Anchor Worms


You fish will seem irritated and will scratch with rough objects in the aquarium. There will be whitish-green thread-like hair coming out of the skin whereas it should be smooth. There will signs of inflammation at the point on the skin where the growth occurs.


There is an infection of anchor worms in your aquarium. These worms will attach themselves to the fish skin and then burrow deep into the muscles. They begin to feed on the fish and reproduce by laying eggs before they die. This damage results in an infection and the abnormal growth which you must treat quickly.


The treatment for Anchor worms in fish is a very hands-on treatment method. The best method is to remove the Anchor worms by hand and quarantine your affected fish. You may have to do the following process a few times.

Using tweezers try to grip them as close to the wound as possible. Periodically dip the fish into the bucket of water to let him get a few breaths before continuing removing the anchor worms.

This is a stressful process for both the owner and fish, but it offers the best chance of successful treatment for Anchor worms.

The next step in the treatment involves adding a chemical treatment to the water to kill off any free-swimming larvae in the water. Use an organophosphorus insecticide such as Ocean Free from Amazon.

Repeat the treatment after 7 days by removing any new anchor worms that have attached themselves to the fish and treat the water again in case there are any new free-swimming larvae.

Tropical Fish Diseases - Symptoms & Treatments 1

Clamp Fin


The fish is not very active and show listless behavior. The fins which should normally be spread out are now folded near the body with the result the fish cannot swim normally.


Clamped fin

Again this is not a specific disease but a symptom on many diseases. There can be many causes for it. Poor water quality may be one of the causes or it could be a parasitic infestation. It is very important for you to further identify the specific disease.                                                                                                             


First, test the water by using a reliable test kit like Master Test Kits available for Freshwater and Saltwater aquariums. Then perform a partial water change to improve the water quality quickly.

Then use a good quality all round fungus treatment such as API PIMAFIX.

That should make a difference in most causes of clamped fin fish disease. This can be used in Freshwater and Saltwater aquariums.

It’s good practice to add 1 tbs. aquarium salt per gallon in a freshwater aquarium to help prevent clamped fins.

Dropsy and Malawi Bloat


The fish will look bloated with scales sticking out. The eyes will also seem extruded. This will look lethargic will seem to labor in breathing and will not eat its feed. Dropsy is an old medical term for a medical condition that today would be more likely called edema—the swelling of soft tissues in a body cavity.


This disease is due to an infection by bacteria. The kidneys of fish fail which results in a build-up of fluids inside its body. Only already weakfish will be affected by this disease. Once a fish becomes diseased it is almost fatal. Some experts recommend that all affected fish be euthanized to prevent the spread of the infection to healthy fish. However, if the infection is detected early, it is possible to save affected fish.


Start by moving the infected fish into a quarantine tank to separate them from the remaining healthy fish in your main aquarium. Whilst the affected fish are quarantined, perform a water change on the original tank and monitor the remaining fish closely for the appearance of other symptoms.

Salt should be added to the hospital quarantine tank, one teaspoon per gallon of water will help prevent the illness spreading further.

Feed the sick fish small quantities of top quality foods including live foods. Antibiotics should be used if the fish does not immediately respond. A broad-spectrum antibiotic specifically formulated for gram-negative bacteria is recommended, such as Melafix.

Like with most tropical fish diseases, prevention is better than cure. Most illnesses come from poor water conditions and other factors like overfeeding, Overcrowding and lack of regular partial water changes.

Fish Ick and White Spot Disease


Saltwater ick

Small white spots that may be slightly raised like sand or sugar grains may appear on the body and gills of the infected fish. Over time these grains may join together to form large white patches. The fish will scratch its body against rocks and stones. In the advanced stage the fish will gasp near the surface as it needs more air. Its fins will clasp by its side. It will not eat its feed. Your immediate attention is required.


This disease is caused by a common parasite found in most aquariums. It is a protozoa and it attaches itself to the fish body, fins, and gills and proliferates when the water temperature of the aquarium drops suddenly due to weather change or water replacement.


Whitespot is one of the most common tropical fish diseases and can be treated by using one of the many whitespot remedies sold online and in your local aquatic store.

Other treatments can also be used in conjunction with a good whitespot medication, like turning up the water temperature to as high as 30°C/86°F if your fish will tolerate it, as this speeds up the life cycle of the parasite. Also add salt — which nine out of ten parasitic diseases don’t like, one teaspoon per gallon. We use Fritz Mardel ick cure which is suitable for Freshwater and Saltwater aquariums.

Fish Fungus


The fungus starts to attack the fish body and it shows as a gray or whitish growth on the on the skin and fins. This grows into a fluffy cottony texture. If not treated the fungus will consume away the fish’s body and your fish will die.


Fish have a mucus layer on their skin which protects their body from the fungus spores and they cannot settle on the fish’s body. If your aquarium is clean your fish will be safe from fungus attack. But if the mucus layer of the fish is damaged due to mishandling, infighting or dirty conditions in the aquarium then it is likely that fungus will affect your fish. Fish that are already weak form some other disease due to bacteria or parasites are susceptible to fungal attack. Ambient conditions in the aquarium such as poor water quality, low temperature, and bad water chemistry can stress the fish and cause fungal growth.


There are many commercial medications available for treating Body Fungus. These tend to be based on organic dyes, like malachite green.

Caution: Antifungal medications are not suitable for all species so isolate the fish in a hospital tank. Fungus infections can spread throughout the aquarium quickly so acting fast is vital.

If you’re new to fishkeeping you should read our Beginners Guide to setting up a fish tank

Gill Flukes


Gill flukes (Dactylogyrus) and skin flukes (Gyrodactylus) are common parasites that affect fishes.

These are also visible as white spots like the skin and gills with the additional eye spots which are not found in Ich infection.  The gills are covered by mucus and they looked they have been chewed.

The gills move rapidly, belly seems hollow and the looks fish looks pale. It scratches its body against objects, its fins appear to be drooping and it exhibits rapid respiration. Once the gills are destroyed the fish dies.


Despite the name, Gill flukes also affect the body as well as the gills. Gill Flukes are not just one disease but a number of parasites which attack the fish. Unlike other diseases, it can infect healthy fish. These parasites will attach to the gills and damages them which stop its ability to function normally. With non-functioning gills, the fish dies of oxygen deprivation. Unlike other health problems in fish, flukes can infect a healthy fish. This outbreak occurs in aquariums with poor ambient conditions such as bad water quality and chemistry, high ammonia content and stress caused to fish by overcrowding.


A number of treatments are available for flukes, those containing Praziquantel are the most effective. Isolate the affected fish if possible and treat with a suitable medication like Praziquantel Treatment for Freshwater and Saltwater Fish which you can purchase from Amazon.

Gill Mites


Gill mites are very common parasites that feed on the blood and skin particles of your fish. These very small parasites are less than 1mm in size, but they can be devastating in any aquarium.

The gill covers of the fish will be partially open and the fish are floating at the surface of the water gasping for air.


This disease is caused by the infestation of tiny mites get attached to the fish’s gills and feed on blood and flesh of the fish. These mites enter the aquarium by fish already infested with these mites.


Treating Gill mites effectively will involve using a combination of sterazin and octozin. This treatment should be repeated in about five days to kill any new hatchlings that were not eliminated with the first round of treatment. You can also use antibiotics to treat any infection that the parasite leaves behind.

Hemorrhagic Septicemai



This disease is caused by a deadly virus called Viral Hemorrhagic Septicemia Virus (VHSV).  It is brought into the aquarium by fish already infected with this deadly virus. It is related to an Ammonia spike in aquarium water, poor water conditions with high amounts of decomposing organic debris. High levels of nitrate and a poor Redox tend to be common when Septicemia is present.


There is no known cure for this virus. Sometimes treating secondary infections with wide spectrum antibiotics will help but unfortunately, the disease is very difficult to cure.

Fish Lice


The lice are large size parasites have eight legs about 5mm to 10 mm which resemble pale crabs. The lice crawl over the fish’s body and use suckers, spines, and hooks to pierce the skin of fish and suck blood. The infested fish get very irritated and restless; they rub themselves with aquarium glass and rocks to rub off the lice from their bodies. Where ever the lice bite the fish it leaves red marks, ulcers, or inflamed spots.


Lice come to the aquarium from fish introduced from outside ponds or from the wild which are already infested by lice. These lice transfer to other fish in the aquarium and the entire brood of fish are infested. The lice bring with them bacteria and viruses which cause other diseases to the fish apart from the damage done by the lice to the fish directly.


A traditional method is to hold the fish in a damp cloth and use tweezers to remove the lice. If you have a freshwater fish that is suffering from lice then bath the fish in a seawater bath (35ppt) for about 5 minutes every day until the parasite falls off.

Once all the parasites have been removed keep an eye out for secondary infections and treat with a multi-purpose parasite chemical treatment.

Prevention is better than cure. So, ensure that you quarantine all new fish if possible and watch out for any Lice infection before adding your new fish back into your main aquarium.

Ragged Tail Fin

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This disease clearly shows when the tail and fins of the fish appear damaged. The tail and looks discolored and frayed.

ragged tail rot


The disease occurs mostly in aquariums with poor environmental conditions including mismatching of fish. This is a progressive disease which may start by a fish injured during bullying and infighting with other fish. Once the tail and fins are damaged, a bacterial infection may set in and the tail and fins lose their color and they progressively fray.


Often the reason for this disease is poor water conditions. The first step in treating the sick fish is to test the water and then make any changes if necessary. This will include a partial water change and also for freshwater fish adding 1 tbs. aquarium salt per gallon will help cure the problem and prevent clamped fins in the future.

Then use a general aquarium fungus treatment. We like API FUNGUS CURE available from Amazon.

Tail, Mouth and Fin Rot


The edges of the fins or tail start to appear to fade color and turn to milky white. The tail and fins look tattered and shredded with decreased length. Fin rot starts at the edge the fish’s fins, destroying more and more tissue until it reaches the base. And then it destroys the body. Your fish will have difficulty swimming normally.


A bacterial infection such as Flavobacterium Columnare, Aeromonas, and Pseudomonas may cause this tail fin and mouth rot in susceptible fish, especially in those fish that are bullied or injured by fin-nipping tank mates. This often occurs in aquariums with poor water conditions and overcrowding of fish where they attack each other and damage their fins.


Treat the fish with obvious fungal diseases using Anti Fungus and Finrot which is perfect for treating most fungus infections.

Observe the behavior of the fish in your aquarium to ensure there is no fighting or fin nipping that will encourage further outbreaks and caused the problem in the first place then address the issue to prevent worsening or repeated infection.



Image credits @ directtropicalfish.co.uk

One or both eyes of the fish become very large and it will seem that they will pop out of their bodies. The eyes look cloudy and sometimes bloodstained. Sometimes the eye gets ruptured. The fish will look abnormal and lethargic in behavior.


The cause of Popeye disease in tropical fish could be due to bacterial infection. Too much-dissolved oxygen in the water may also lead to this condition. This condition is also called exophthalmia, the excess oxygen results in hemorrhage produced in the capillaries of the eye socket, affecting one or both eyes. The root cause of this disease usually is chronic poor water conditions for extended periods of time.


Remove all affected fish immediately and treat them separately from the main aquarium if possible. Large daily water changes will help.  Epsom salts have been used with good results to draw the fluid out from the affected eye.

Add one tablespoon per 5 gallons of water for at least three days, longer if necessary. Epsom salts aren’t really salt it’s (sodium chloride) which is a Magnesium Sulfate. Water quality is often the problem, conduct a 50 percent water change as soon as possible.

Hole in the head


Small holes appear on the head of the fish. Lesions can appear on the flanks too. Fish often have yellowish mucous trailing from them. Their color fade, they show lethargic behavior and have difficulty is swimming normally. The affected fish stop eating the feed you give. Not all species of fish show the same symptoms and do not always develop lesions to the same extent.


Hole in the head disease is caused by protozoa and is usually a secondary infection. Low levels of the protozoa that cause holes in the head disease live within the fish. However, the trigger of this disease is possibly the use of activated carbon in closed aquarium ecosystems. Other factors can include nutritional deficiencies, especially key vitamins and dietary iodine. Water quality can also play an important role. Check nitrate in water, as aquariums with high nitrate levels can cause fish to develop this disease.


First, quarantine the infected fish and then treat with a general anti-pathogenic medicine like API GENERAL TREATMENT.  Other treatments include direct injections from your vet or medicated foods.

Stress and poor water conditions play a role in this disease, so ensure you provide the best possible conditions for your fish. Carryout a partial water change before and after treatment even if you have quarantined the infected fish to prevent more fish from contracting the disease.

Improvements in nutrition have been shown to benefit affected fish and can aid their recovery quicker.

Velvet Fish Disease


This is a common disease in aquarium fish. It is also called the ‘Gold Dust disease’. Fine yellow or light brown film forms on the skin of the fish and eventually, the skin will peel off.

The fish has clamped fins and will scratch its body with hard surfaces. Show lethargic behavior with rapid breathing. Does not feed well and lose body weight.


This disease is caused by a parasite called Oödinium and has the potential to kill every creature in your aquarium if left untreated. This parasite attaches itself to the fish’s skin and gills eating up the flesh, destroying the body. Once it’s done feeding off the fish it will drop off – dividing into dozens of cells and thereby contaminating your entire tank. The main cause of their proliferation is poorly maintained aquarium, abrupt changes in water temperature, poor water quality, adding new fish without quarantining, and the introduction of infected plants.


Velvet is highly contagious and should be treated as soon as possible. Copper sulfate is the treatment of choice. It should be used according to the manufacturer’s instructions. Other medicines can be used like Atabrine (Quinacrine hydrochloride).

Because Oödinium is dependent on light, dimming the aquarium lights will help reduce the infestation. Increasing the water temperature to 82 F will also speed up the process, and adding salt to the water will help control the spread of the parasite.

When using any form of tropical fish medication you should remove all activate carbon.

Final Thoughts – Tropical Fish Diseases

If you’re searching online for tropical fish diseases then you probably have a fish that is suffering from one of the diseases above. Applying the most appropriate treatment will give them the best chance of survival.

Our pets and fish are very important to us and it’s difficult to take them to see a vet or specialist when they become ill, so their only chance of survival lies with us. If you have the correct information and diagnosis then they will have the best chance of survival.

It’s our responsibility as tropical fish keepers to look after and care for our fish. So, ensure you take care of them from the minute you notice they are becoming sick.

Fishkeeping Forever takes no responsibility for diagnosing the exact problem with your tropical fish, this should be used purely as a guide for providing the correct treatment.

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