Fish Disease – Signs, Causes, And Cures

Goldfish Fish Aquarium Underwater Fishbowl

It’s a nice lazy day and you’re just kicking back and enjoying the aquarium you have worked so hard to set up. But wait, something’s off. One of your fish looks like he has been rolling in the sand. And another appears to have less fins than you recall. And still another is bloated he looks like he is going to burst. All in all, it looks as though your fish are sick! Yup, keep fish long enough and it is something you’ll have to face eventually, and usually fairly early unfortunately. You see, illness is often preventable, but typically we only learn how to do so after doing it wrong the first time. But fear not! Many disorders can be turned around if seen early and treated correctly.

Spotting Illness

So how can you tell that a fish is sick in the first place? It’s not like they are going to tap you on the shoulder and allow you to know. For the most part the only way you’ll know something is wrong is through careful observation of their appearance and Opossum Poop. Hopefully you are already fairly well acquainted with what might be considered normal for your fish and can thus see when something is off.

-paleness/color change

-clamped fins (the fins are held near the body)

-scratching or rubbing against objects in the tank

-heavy breathing


-decreased activity

… and of course the more obvious signs like visible swelling, nausea, and such.

Try to have a few minutes each day to check for any signs that something is amiss. Feeding time gives an ideal opportunity to do this as most fish are at their most active when there’s a meal to be consumed. A disease caught early is far easier to treat and the odds of the affected fish surviving the ordeal are far greater. For many ailments your fish may face by the time it’s blatantly obvious it’s too late.

Quarantine Tanks

Of course one step better than treating your fish once they get sick is preventing it from happening in the first location. The absolute best way to prevent diseases from reaching your tank is using a quarantine tank. A quarantine tank is essentially only a small bare bones aquarium set up where new arrivals can spend a week or 2 before entering your main installation. This gives you ample time to be certain that your fresh fish are in good health before they have a chance to potentially spread any diseases to your other fish. Additionally, it gives new arrivals a opportunity to get over the stress of moving in a quiet and peaceful atmosphere. And if a problem does arise with the shredder already isolated makes treatment much easier as well. Finally, in the event that a problem does hit the fish in the main aquarium the septic tank can serve as a hospital tank also, preventing the further spread of disease and providing a safer and more controlled environment for the use of any remedies.

Besides a quarantine tank, keeping your fish in good general health goes a long way towards preventing any illness from taking hold. Most common diseases often arise in fish only if their health is already compromised. What causes their health to become compromised? Nearly all the time the offender is poor water quality. A fish trying to reside in filthy water in kind of like you trying to live in a house filled with smoke- it’s unlikely you’re going to be in the best of health. Keeping on top of your aquarium installation’s maintenance is key to keeping your fish healthy and disease free. Therefore, should your fish ever become ill your first step should always be to ensure that the water is in excellent condition. All the vital parameters, such as nitrate, ammonia, pH, and temperature, should be checked. Always be leery of any equipment or decor that was recently added to the tank as well which could be leeching something toxic into the water. Andif poor water quality isn’t the origin of this illness, a water change is never a bad idea When it comes to recovery the cleaner the water the better.

About Medications

Often people go straight for the medications at the first sign of an illness in their fish, usually without even knowing what exactly is incorrect. This is a bad move. Positive identification of a disease is absolutely essential before beginning program of any medication. Many medications aren’t exactly easy on your fish meaning using the wrong one could wind up further stressing your fish without curing their illness, likely leading to death. Still, should you encounter a disorder where a medication is applicable it can be a true life saver. Just be certain to remove any carbon from the filter prior to beginning treatment as it will soak up the medicine until it has a chance to act. And, it should go without saying that the directions should be followed to a T. Pay special attention to any warnings dealing with species that the medication should not be used with. Some, for instance, will kills snails and plants if there are some in the tank.

There are tons and tons of diseases your fish may face- much more than what are listed here. However, many of them are fairly rare, affecting just a few specific species or just arising under specific conditions. Instead, this list tries to cover just the most common ones that most aquarists have a tendency to run into.

Signs- red irritated gills, fish gasping for air at the surface, most common in fresh tanks

As the common name of’new tank syndrome’ suggests, this is typically only a problem in freshly setup aquariums, though it can happen is older systems if the filtration system is severely damaged. Some are really quite useful, and necessary, to your aquarium. Their task is to process the fish’s waste from highly toxic substances, namely ammonia, to compounds they can more easily tolerate. The process of establishing these germs in a brand new system is called cycling. Unfortunately, this step is often skipped leading to a buildup of ammonia which in short order contributes to dead fish.

Remedy: water changes

To solve this problem you basically just need to keep the water clean through regular water changes before the bacteria have established themselves and can take over. A test kit for ammonia is very helpful here as ideally you want to keep the ammonia level under 1ppm. Typically you’ll need to do a small water change daily for a few weeks to allow the cycle to complete while keeping the tank habitable to your fish. Keeping feedings light in this time may also help keep the waste load low which in turn keeps the water cleaner.

Fish Fungus

Signs- fish has fuzzy whitish globs or patches attached to its fins and/or body

Just like a lot a ailments you are likely to encounter, fish fungus usually appears on fish whose health is already compromised. The fungi that cause it are quite common and pretty much guaranteed to be in the tank at all times. This normally wouldn’t be a problem, but when a fish is already in poor shape the fungus can find a hold very easily. It often begins at the website of an injury, which may be anything from minor scrapes to major sores, and spreads quickly from there.

Treatment: medication for fungal infections

The best way to treat fungal infections is with medication developed for them. Of course making sure the tank is in good shape is key and the fish is likely already in poor shape and needs all the help he can get recovering. As a side note, many remedies for fungal infections also work against bacterial infections that can bring some added benefit if the fish’s initial poor health was caused by one.

Signals – fish is covered in lightly colored specks or has a dusty look


Ask people to name a frequent fish disease and ick is most likely the one that you’ll get. It seems just about everyone who’s ever maintained fish has had to handle it at some point or another. Furthermore, it’s quite easy to spot compared to other diseases and so seems to stick with people. When you haven’t encountered it before, ick is a parasite that burrows into the fish’s skin causing little white spots that make it appear like your fish has been salted. Outbreaks often occur following the addition of new fish, which bring ick along with them, although it can also limp along in a tank for a very long time until conditions are favorable for a burst. Like nearly every disease, favorable conditions means fish in poor health with the most common reason being poor water quality.


Velvet is less common but still worth mentioning. It is another parasite that behaves much like ick, appearing as spots on the skin.

Remedy: medication for parasites

Treatment for both ick and velvet is pretty much the same. They are both parasites with a similar life cycle- part of which is attached to a fish and part of which is spent free swimming. Killing them is more or less impossible while they’re safely burrowed under the fish’s skin. It’s only when they emerge into the open water to look for a new host that they are vulnerable. This means treatment can take some time. Medication needs to be applied for an elongated period to wait out the parasite’s natural life cycle, which may take up to a month. Raising the temperature of the aquarium a couple of degrees can help speed things up a bit. So, in case you move all of your fish into quarantine for treatment, any parasites left in the primary tank will die off after about a month.


Signs- fish is bloated, possibly with the scales protruding giving it a pine cone look

Dropsy is not a disease itself but rather the physical outcome of another ailment, usually a bacterial infection though it could be caused by any number of different things. The swelling is caused by by a buildup of fluid in the fish’s body cavity.

Treatment: medication for bacterial diseases, aquarium salt

Unfortunately by the time the signs are clearly visible it is often too late to save the fish. Still, the best strategy is to move the fish to quarantine and begin administering an antibiotic, preferably in the shape of an medicated food. Adding a small amount of aquarium salt may also help the fish expel some of the excess fluid thereby relieving the swelling. Use approximately one tablespoon per five gallons.

Swim Bladder

Signals – fish has difficulty maintaining equilibrium and may have difficulty controlling thickness

A fish’s swim bladder is kind of like a ballast tank in a submarine, just with air instead of water. They use it to keep themselves upright and in the correct depth. When it becomes damaged or otherwise perturbed the fish is no longer able to control this air and so will typically either sink to the bottom or float to the top, often in an off-kilter orientation.

Treatment: fasting/cooked peas, medicine for bacterial diseases

Unfortunately there’s not a lot of consensus on the specific cause (and in fact there are at least a couple possible causes) or how to deal with it. Making sure the tank’s chemistry is in great shape should be your first step of course, as it should be with any problem. One frequent cause is a blockage in the fish’s digestive tract. The common solution for this is shelled cooked peas (they are sorta the go-to fish laxative). Backing off on feedings for a couple of days can also help. If not then it might be the symptom of a larger disease in which case a medication can be tried. Unfortunately it can also occasionally arise because of injury sustained during transportation in which case there is not much that can be done. In these situations all you can do is give the fish a place to recuperate and hope for the best.

Signals – fish includes a protruding eye

A pretty self explanatory name, the fish’s eye or eyes bulge out from the fish’s head as though they’re on the brink of falling out completely. It’s basically an inflammation of the eye causing it to swell and protrude. Once again this is not so much linked to any one specific cause but instead may originate from a few possible sources, namely injury or an infection.

Therapy: improve conditions, medication for bacterial infections, aquarium salt

Injury due to fighting or possibly from bumping into something is most likely the most common. A good indicator that this is a the cause is if only one eye is affected. In cases like this the best you can do is stop any fighting and provide your fish with a calm home to recover.

Another possibility is a bacterial infection. If both eyes are popped then this is more likely, though the fish should still be assessed for signs of injury or fighting. A good medication is the best course of action here.

Finally, another thing you may try is aquarium salts. Add one tablespoon per five gallons and watch to see if it has any effect. Bear in mind this can help alleviate the swelling but won’t resolve the underlying problem and as always your first step should be to guarantee that the water is in great shape.

Cloudy Eye

Signals – fish has a cloudy eye

The creatures of the world have all kinds of interesting eye with various colours and shapes and whatnot. One thing they all have in common, however, is that the center is clear and nice. If you ever notice your fish’s eyes or eye becoming milky then something isn’t quite right.

treatment: improve conditions, medication for bacterial infections

There are a handful motives a fish’s eye may become cloudy. Parasites or germs are possible causes, particularly if the eye was hurt. Poor diet or even cataracts as a result of old age are possible culprits also. However, the most likely cause falls in line with so many different problems- poor water quality. Getting the tank is good shape should be your first concern if your fish develops cloudy eyes. Pay special attention to the pH as a particularly low pH is thought to contribute to this issue. Check that you are feeding your fish an proper diet also. With better water quality and a proper diet the problem should clear in a couple weeks. However, if the problem does not clear after several weeks with improved conditions an antibiotic could be attempted.

Hole in the Head/Lateral Line Disease

Signs- fish has holes in its head

The name is pretty self explanatory, and the symptoms are easy to spot, so all that leaves is the cause. Why are there undesirable holes on your fish’s head? Unfortunately there’s no consensus on the precise cause. It may be brought about by some specific pathogen, but none has been identified as of yet. Some think overuse of activated carbon or nutrient deficiencies might have something to do with it also.

Treatment: improve conditions, diet change

Ultimately, the best course of action is to enhance conditions as much as you can for your fish. Step up the water changes and try removing any activated carbon from your filtration. Try to include as much variety to your fish’s diet as possible. Frozen as well as vitamin enriched flake foods are great sources of vital nutrients your fish might be lacking.

Fin Rot

Signals – the fish’s fins are deteriorating

Fin rot is another disorder that’s not so much about a particular contagion rather than a consequence of the fish’s overall health. Fin rot typically only affects fish which are already stressed or weak because of something else like poor water quality, malnutrition, bullying, or perhaps even some other sickness, at which point bacteria move in and begin feasting on your poor fish’s fins.

Your first course of action should be to ascertain why the fish’s health has slipped in the first place and correct it. Check the water quality and switch to high quality vitamin enriched foods if you have not already.

Again, the majority of the time health problems come down to a water quality problem. Keeping on top of your aquarium maintenance program is the best way to prevent problems in the first location. Likewise, if an illness should attack checking the water’s parameters should be your first step. Many problems will clear on their own with improved conditions. And when a drug becomes necessary make sure to follow the directions extremely closely. An overdose of medication can be just as bad if not worse than the illness itself.

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