Columnaris vs Ich – Our Helpful and Scientific Guide

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Columnaris vs Ich

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Columnaris and Ich are two common diseases that can affect almost any species of tropical fish.

Beginner aquarists often confuse the two diseases. However, both conditions have different causes and require different treatments, so it’s imperative that you can distinguish between the two.

If your fish are sick and you think Columnaris or Ich might be to blame, you need to read this guide and learn how to recognize, treat, and prevent these conditions.

Columnaris vs Ich

The first thing to know is that these two common types of fish diseases have different causes.

Columnaris is caused by a bacterium called Flexibacter columnare, whereas Ich, or White Spot Disease, is caused by an aquatic parasite called Ichthyophthirius multifiliis.

Columnaris only affects freshwater fishes, whereas Ich has a freshwater and saltwater form, so basically, no fish is safe!

Now, let’s find out more about each disease, including how to recognize and treat them both.


betta fish with columnaris

Columnaris is often assumed by beginner fish keepers to be a fungal infection because of the lesions’ cotton-like appearance. However, it’s actually a common bacterial infection that attacks wild and tank-kept freshwater fish.

The condition is especially common in catfish and livebearers, although any fish species can be affected.

The disease gets its name from the causative rod or column-shaped bacteria and is also commonly called saddleback disease, cotton wool disease, cotton mouth disease, and guppy disease.

What Are the Symptoms of Columnaris?

Columnaris is a bacterial disease that begins to manifest itself as patches of white or gray on the fish’s gills, head, and fins.

These lesions can spread quite slowly in chronic cases, often taking quite a few days before the fish dies. However, in acute infections, the lesions can spread extremely rapidly, often resulting in mass fish kills of formerly healthy fish within a few hours.

Typical symptoms of Columnaris include:

  • Patches of white or gray on the fish’s fins, head, and gills
  • Saddle-like lesions on the fish’s back that extend down the creature’s sides
  • Cotton-like growths around the fish’s mouth
  • Torn or frayed fins
  • Loss of appetite
  • Lethargy

As the disease progresses, the lesions sometimes turn brown or yellowish, ringed with reddened areas.

The fish’s mouth eventually starts to rot away, and the fins appear ripped and ragged. Columnaris also affects the fish’s gills, causing the gill filaments to disintegrate so that the fish can’t breathe.

Sometimes, although less commonly, the infection attacks the fish internally and presents no external symptoms other than a loss of appetite and lethargy.

What Causes Columnaris?

Columnaris bacteria are most likely to attack fish that are stressed. Stress in aquarium fish has many causes, including:

  • Handling and shipping
  • Poor water quality
  • Incorrect water conditions
  • Overcrowding
  • Incorrect, poor-quality diet
  • Temperature shock

The Columnaris bacteria can get into the fish via the mouth, gills, or tiny skin wounds.

But where do the bacteria come from in the first place?

Columnaris is present in many aquariums, only attacking weak or stressed fish. The disease can be spread through foods, contaminated fish nets, and decorations imported from an infected tank.

If you buy any new fish, it’s possible that they could also bring Columnaris into your aquarium.

How To Treat Columnaris

Diseased fish suffering from Columnaris can be treated with a course of antibiotics.

You can also use chemical treatments in your aquarium water, although we recommend setting up a quarantine tank rather than dosing your main tank unnecessarily.

Effective Columnaris treatments include:

  • Acriflavine
  • Furan
  • Copper sulfate
  • Terramycin

If using any treatment containing copper, be sure to remove snails or shrimp from your tank. These creatures are highly sensitive to copper, and exposure to it can kill them.

Salt baths can be helpful in preventing the spread of Columnaris by reducing fish stress and killing any shed bacteria in the water. However, many catfish species can be highly sensitive to salt, so we recommend caution if you decide to use it.

Preventing Columnaris

Columnaris bacteria thrive on organic waste. Therefore, a dirty tank provides the perfect environment for this disease.

Keep your tank clean by carrying out partial water changes each week. Use an aquarium vacuum to remove waste from the substrate and around the tank bottom before it has a chance to decompose and release harmful ammonia into the water.

Offer your fish a correct, high-quality diet to prevent stress, avoid overcrowding your tank, and ensure that the water temperature is correct for the species you keep.

When you buy any new fish or other livestock, always place them in quarantine for at least two weeks before introducing the newbies to your main display aquarium.

After using nets, containers, and other aquarium equipment, always clean and disinfect them thoroughly to prevent the spreading of diseases. You can use a commercial fish-safe product, such as Benzalkonium Chloride solution, or use a solution of 3% hydrogen peroxide.

Rinse all equipment thoroughly after cleaning to remove all traces of disinfectant.

Ich (White Spot Disease)

white spot disease

Ich is an extremely common disease that almost all fish keepers will encounter at some point in their fishkeeping journey.

There are two forms of Ich that can affect both freshwater and saltwater fish tanks. So, whether you have a tropical freshwater tank, a coldwater goldfish setup, a reef aquarium, or a marine tank, you’re pretty much guaranteed to see Ich from time to time!

Unlike Columnaris, freshwater Ich is caused by an aquatic parasite known as Ichthyophthirius multifiliis. The saltwater equivalent of this disease is caused by the Cryptocaryon irritans parasite.

What Are the Symptoms of Ich?

Ich is pretty easy to diagnose in both marine and freshwater fish. The symptoms to watch out for include:

  • Fish flicking or flashing against solid objects in the tank in an attempt to relieve the irritation caused by the parasites
  • A rash of tiny white spots across the fish’s body, gills, and fins
  • Loss of scales and bruising as a result of traumatic contact with objects in the aquarium
  • Loss of appetite
  • Lethargy

You might also notice your sick fish breathing rapidly or lying on the tank bottom. That stage of the disease usually happens if the fish’s gills are clogged with parasites, preventing the fish from breathing.

Incorrect Diagnosis

If you have goldfish, you might notice small white bumps on the fish’s head. Those bumps look much like Ich but are simply a sign that you have a male goldfish that is in breeding condition.

Another condition that can be mistaken for Ich is Lymphocystis. Lymphocystis is a virus that produces white spots on the fins and is best diagnosed by a vet.

What Causes Ich?

Much like the bacteria that causes Columnaris, the parasite that causes Ich is often already present in the aquarium.

Essentially, anything that causes stress in fish leaves them open to parasite attack.

For example, when fish are stressed, perhaps following transportation from the fish store, their immune system is compromised, leaving the creatures weakened and vulnerable to attack by the Ich parasite.

New fish often bring Ich with them, rapidly infecting the entire aquarium. Unfortunately, fish often don’t appear sick until several life cycles of the parasite are complete. That takes a few days or a few weeks, depending on the tank water temperature.

Other causes of Ich can include:

  • Using infected tank décor or filter media from another tank
  • Not disinfecting equipment before use
  • Emptying infected water from a fish bag into your main tank
  • Adding new aquatic plants to your tank that might harbor Ich tomonts

So, what can you do if your fish has Ich? Luckily, if you spot it early, you can usually treat Ich successfully and quickly.

How To Treat Ich in Freshwater Fish

Both freshwater and saltwater Ich parasites have a complex lifecycle, and that can make them challenging to treat.

The white spots you see on your fish are the large feeding stage (trophont) of the Ich parasite. The trophont stage is highly resistant to treatment. However, the free-swimming (theront) stage is the only time in Ich’s life stage that can be killed off successfully.

When you know that it only needs one trophont to reproduce after leaving its fish host to produce 1,000 new theronts (infectious organisms) into your tank, you can see just how fast infections can spread.

The parasite’s lifecycle is highly temperature dependent. Essentially, in warm water, there are fewer days between the different life stages than in cooler conditions.


There are many effective treatment options in the form of antiparasitic medications that will kill Ich, provided that you use them correctly and follow the manufacturer’s instructions carefully.

Do not overdose your fish tank, as that can harm your fish. Underdosing might not kill off the Ich parasites. So, it’s essential to get the dosage correct.

Follow the full course of treatment, ideally treating your tank on alternate days for ten to 14 days. On the days between dosing your tank, carry out partial water changes.

Throughout the treatment, observe your fish to be sure that no more white spots appear following treatment.


You can use an increased water temperature to eliminate the Ich parasite from your fish tank.

The Ich parasite can’t tolerate a water temperature of 86° F for longer than two weeks. Before raising the tank temperature, double-check that your fish can cope with water of that temperature, and reduce the temperature gradually following treatment.

Make any temperature adjustments gradually so that you don’t stress your fish. So, increase the water temperature by a couple of degrees a day until it reaches 86° F.

How To Prevent Ich

Ich can be prevented by quarantining any new fish, inverts, and plants for at least two weeks before adding them to your main tank.

Always disinfect equipment thoroughly before using it.

Quarantining plants away from fish and other livestock for at least two weeks can be effective against Ich. That’s because the parasite will have nothing to feed on, breaking the lifecycle, and causing the pests to die off.

Ensure that your fish don’t become stressed by keeping your tank clean, well-maintained, and at the correct temperature for your fish. Feed your fish a correct, varied, high-quality diet, and remove any aggressive tank mates to ensure a harmonious, peaceful tank.


In this section of our guide, we answer some of the most commonly asked questions about treating Ich and Columnaris.

Q: What Are the Symptoms of Columnaris?

A: At first, you might notice grayish or white patches on the fish’s head and around the gills and fins. Those lesions are typically seen as pale, dull areas that contrast with the fish’s usually shiny scales.

As the disease progresses, the lesions turn brownish or yellowish and are often ringed with red.

The disease is often nicknamed “saddleback disease” since the lesions often extend down the sides of the infected fish’s body. Sometimes, cotton-like patches form around the fish’s mouth, and the tissue eventually starts to rot away.

Often, the fins develop a torn, frayed appearance. If the fish’s gills are affected, the filaments inside them degrade, leaving the fish struggling to breathe.

Q: What Are the First Signs of Ich in Fish?

A: Initially, fish infected with Ich or White Spot Disease will flick or rub against objects in the aquarium in an attempt to relieve the irritation caused by the Ichthyophthirius multifiliis parasites.

Within a few days, the fish develops a scattering of tiny white spots like grains of sand across its fins, gills, and body.

Q: What Is Columnaris Caused By?

A: Columnaris is a bacterial infection that’s caused by the aerobic gram-negative bacterium Flavobacterium columnare.

Q: Does Aquarium Salt Help To Treat Columnaris?

A: Salt baths can help in treating Columnaris because it disinfects water containing the Flavobacterium columnare cells that are shed by infected fish, preventing the spread of the disease.

Q: What Temperature Kills Ich?

A: Most strains of Ichthyophthirius multifiliis cannot survive a water temperature of 86° F for longer than two weeks.

So, raise the tank temperature by a couple of degrees each day until you reach 86° F. Following treatment, reduce the temperature gradually to the correct level for your livestock.

Most tropical fish can withstand that higher temperature for short periods but always research your fish thoroughly before you raise the temperature in your tank.

Final Thoughts

I hope you enjoyed our article comparing Columnaris and Ich. If you found the information helpful, please share the guide before you go!

As you can see, there are quite a few key differences between both these common diseases in fish. However, Columnaris is a bacterial disease, whereas Ich is caused by a parasite.

Both these diseases don’t attack healthy fish. Usually, only fish that are already sick, injured, or stressed are infected.

Poor water conditions and an unsuitable diet both contribute to stress, as does overcrowding or bullying by tank mates. So, correcting those issues can help to keep your fish healthy.

When you buy new fish, invertebrates, or plants, always place them in quarantine for at least two to four weeks to be sure they are disease-free before introducing the newcomers to your main tank.

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