Recognizing Common Diseases in Freshwater Fish

Getting Started

Kin Hubbard said it best: 'No one can feel as helpless as the owner of a sink goldfish'. That pretty much sums up what any aquarium owner feels when they first discover their fish are not well. Don't despair! Not all fish diseases mean you little friends will soon be taking a trip on the porcelain express. In fact many common ailments of freshwater fish can be cured. Sadly, many diseases that can be cured are often fatal if left untreated.

It is important to note how your fish are behaving on a daily basis. This will help you determine if their behavior is normal or not. It will also help to do some research as far as what kinds of behaviors are considered normal for your species of fish. Plecos do not behave the same as a tetra, if your tetra starts to act like a pleco (spending all of its time sitting on the bottom) you might have a problem.

It is imperative that you maintain good water quality in your aquarium. You can improve the health of your fish simply by making sure the water in which it lives meets its needs. When their water quality needs are not met fish do not behave normally. A perfect example of this is that fish typically are sluggish when the water temperature gets too cold. Slowly warming the water up to their desired temperature will make the fish more active.

Once you know that you have good water quality and have gotten to know the behavior of your fish it is easier to determine if they are sick. This puts you on the path to, hopefully, treating your fish before it gets too late.

The white spots characteristic of ich
The white spots characteristic of ich

Side Note: Killing Ich With Heat

Some articles suggest that you can kill ich with heat. This makes logical sense. The water becomes too hot for the ich to survive. Once you have acclimated your tank to the temperature desired it needs to be maintained for at least ten days. This will ensure that all of the parasites have been killed. That being said do not attempt this unless you are sure that your fish can handle the temperature. High temperatures can stress out, or even kill, your fish and this is not good when the fish is already stressed from the parasite.

Ichthyophthirius multifiliis

Commonly known as ich, ick, or white spot disease. Simply put ich is a parasite. It is easily diagnosed by the appearance of white spots that look like salt or sugar grains. Other signs of ich include: loos of appetite, labored breathing, and flashing (when fish rub their bodies on the substrate or decorations). Of course, these other symptoms could also point to many other diseases, this is why the characteristic white spots are so important in this diagnosis.

Ich is a nasty parasite. It exists in three different stages. The first stage is when the parasite is visible with the naked eye, these are the white spots you see on your fish. After a few days of feeding upon the fish the parasite leaves the fish. Once the parasite leaves the fish it enters the second stage of its life cycle. This free-swimming stage is the time when it can be treated with chemicals. However, once it settles into the substrate it begins its reproductive cycle and is no longer affected by chemical treatments. When the new parasites emerge from the substrate and start to look for a new host it has entered the third life stage. If they do not find a host in a few days they will die. Again, while they are swimming in the water, and not attached to anything, the parasite can be killed by chemicals. If left untreated ich has a 100% mortality rate.

Now that you know what is attaching your fish how do you kill it? There are a few different methods to choose from. As a hobbyist aquarist, and a professional aquarist, I like to use several different methods of treatment. Ich is not something to take lightly. If I see it in my system I treat it as aggressively as I can. The first approach is to increase the temperature of your water, as long as your fish can tolerate it that is. This will help speed up the life cycle of the parasite. Why would you want that? Because, there are only two times when you can kill it with chemicals: after it falls off your fish before it reproduces and after the new parasites are born before they attach themselves to your fish. Another approach is to add salt to your tank. A tablespoon of aquarium salt per gallon of water is a good rule to go by. Remember you are not trying to make saltwater, but rather make it uncomfortable for the ich to live.

Medications are often the home aquarists' 'go to' when treating ich. They are easy enough to find since nearly every pet store sells them. (That should give you an idea of how common ich is) The most common chemicals used are formalin, malachite green, or a combination of both of these. The type of fish you have can dictate which chemicals to use, especially since some chemicals are not safe for some kinds of fish. As always follow the directions completely when using any chemicals. Typically you will need to remove your carbon filtration when medicating and do a water change daily before re-dosing.

My personal choice for ich treatment is an immediate water change (gravel washing will help get rid of the reproducing parasites in the substrate), increasing the temperature to around 80 degrees, adding a little bit a salt (just a tablespoon), and then treating with chemicals. Like I said I like an aggressive approach to ich treatment. Ich is not welcome in my tank, and I make it obvious.

The body cavity looks swollen and the scales are raised giving the fish a pinecone appearance.
The body cavity looks swollen and the scales are raised giving the fish a pinecone appearance.


Contrary to what many people believe dropsy is not actually a disease. It is a symptom that signals an array of underlying causes; parasites, bacterial infections, or even liver failure. So what exactly is dropsy? It is a build up of fluid in the body cavity of the fish. Often the fish looks bloated with raised scales. The fish almost resembles a pinecone. Since there are so many different causes dropsy must be taken seriously. In many cases once the issue has progressed to the point of dropsy it may already be too late for the fish.

If you want to try to save the fish immediate action must be taken. The first step would be to quarantine the fish. This should prevent whatever has afflicted your fish from infecting the rest of the collection. The next step is to attempt to treat. Since dropsy has many different causes it is best to just get medication that says it helps to treat dropsy. Many medications for bacterial and parasitic infections have this right on the label. However, if the dropsy is caused by liver failure there is very little that you can do for this fish.

The protruding eye makes popeye easy to distinguish
The protruding eye makes popeye easy to distinguish


Popeye is easy enough to identify. One, or both, of the fish's eye visibly bulge from the body. The eye may even appear to be cloudy. The swollen eye is caused by a build up of fluids in the fish's eye. This can have many causes, some with treatments simpler than others. If the popeye is effecting both eyes it is possible that poor water quality may be the culprit. Simply do a water change and ensure that you treat the water properly for your fish. If water quality was the problem the popeye should clear up on its own with a little time.

If the popeye is only in one eye it is likely to have been caused by the fish bumping into something in the tank. Essentially this is like the fish getting a bruise, or a knot after running into a wall. If this is the case then the popeye will go away on its own in time, just like with bruises with people.

However, if after a water change and a few days the popeye does not go away it could be a bacterial or fungal infection. If this is the case you will need to medicate your fish with either a bacterial or fungal medication. Sometimes trail and error is needed in treating fish, this is one of those cases.

What would be your first course of action if you suspect your fish are sick?

  • Check water quality and preform a water change if need be
  • Wait it out
  • Immediately treat with whatever chemicals you have
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Don't Freak Out!

The most important thing to keep in mind when you are dealing with sick fish is that it is going to be ok. Your ultimate goal is to eradicate whatever it is that is afflicting your fish. Sometimes that takes time. You are not going to results overnight, not usually anyway. Sometimes you need to combine methods or try different things. Either way you need to be patient. The fish is either going to die or it is going to live. Thankfully most diseases are fast acting so the fish will not suffer long. This also means that if you are going to try to treat your fish you need to do it at the first sign of trouble.

In Conclusion

There are many more diseases out there that affect freshwater fish. Those three are just some of the most common ailments that home aquarists deal with. Sooner or later chances are very high that you will have to deal with an outbreak of ich. Sometimes you don't learn things until you have to treat, or even lose fish to disease.

It is best to take the approach of preparing for the worse and hoping for the best. Many hobbyists learn after their first tango with disease that it is best to keep a fishy first aide kit. What should you include in such a kit? Any chemicals you might need to change the quality of your water. This should be self explanatory at this point. It is also best to have some sort of ich treatment, a bacterial infection medication, and something for fungal infections. This way you will have the bases covered incase something happens. If nothing you have on hand works then it would be time to take a trip to the pet store and see if there is anything else available for your fish. Trust me, if you discover that your fish has ich at 10 on a Sunday night you will be glad that you have everything that you need to deal with it on hand. Especially since waiting a day to go to the store could mean that your fish will not be alive when you get home from work the next day.

Keep calm. With diligence and a little luck you can save your fish from many ailments. I hope you never have to deal with the world of parasites, fungus, and bacteria, but if you do I wish you the best of luck.

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SAM ELDER profile image

SAM ELDER 3 years ago from Home

Actually the reason of rising temperature is to help making the circle or live of ich move faster, which helps the ich's "eggs" hatch faster. So the treatment duration is no longer than couple of days if you use medicine.

Higher temperature is also affects fishes immune system and many times by rising temperature and by adding a small portion of pure sea salt into the tank can help to get rid of ich. Temperature should be adjusted as slow as possible to allow fish to get used to it and it must never exceed 32C.

isharkbait profile image

isharkbait 3 years ago Author

The reason for treating for treating ich over a several day period is because the parasite, even with raised temperatures, has a life cycle of a few days. At 80 degrees (I don't go any higher because I do not have fish that can tolerate temperatures much higher, so people raise the temperatures as high as 90-95 degrees.) ich has a lifecycle of around 4-5 days. Personally I treat between 8-10 days to make sure that whatever I didn't kill in the first cycle gets killed in the second.

It is really up to the aquarist how long they want to treat. Some people stop treatment as soon as they no loner see any white spots. The big downside to this is that you haven't killed all of the parasites and you risk a relapse. Obviously you do not want to overly stress your fish. As my fish handle medication fairly well, they continue to eat and exhibit normal behaviors, I can afford to treat for 8-10 days. As I have never had a relapse of ich I am confident that my methods work.

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