Why Are Fish Rubbing Themselves Against Rocks and Plants?

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Fish exhibit a variety of behaviors depending on the species and even the specimen. All fish are unique animals and display amazing diversity in terms of temperament and demeanor.

That being said, some behaviors are universal, and they speak volumes about your fish’s physical or psychological state.

Today, we will discuss a common behavior that all fish will display at some point: rubbing against the environment.

7 Reasons Fish are Rubbing Against Plants and Rocks

You may have seen your fish exhibiting this behavior occasionally, but you didn’t make anything of it.

If you’re not familiar with the fish’s behavior, you may have considered the display normal, but that’s not always the case.

I present to you the 7 most widespread reasons why fish rub themselves against rocks, plants, and other submerged elements:

1. Natural Behavior

Some fish are simply like that. They are more energetic and dominant than others, so they need to make a statement in that regard.

It’s not unusual for some fish to rub against rocks in an attempt to intimidate other fish, attract the females’ attention, or even out of boredom.

Some fish are simply clumsier, causing them to rub against plants and rocks by mistake. Or they simply like the feeling, so they will indulge in it more often.

The key here is learning how to distinguish between harmless and normal behavior and abnormal instances. We’ll get into that, don’t you worry!

2. External Parasite

We’re talking about skin parasites, to be more precise, but internal parasites may also trigger this behavior. The fish will experience itching and attempt to mitigate the sensation by rubbing against various objects.

You can tell that something’s not right if the fish is quite jittery about it.

Fish infected with parasites tend to rub against rocks and plants more aggressively and also display physical signs warning of their problems.

Skin lesions, missing scales, white spots or discoloration, or skin ulcerations are pretty good indicators that something’s not normal about the situation. At this point, you need to weigh the situation more carefully.

There are plenty of external and internal parasites, each with its own physiology, symptoms, and long-term effects.

Ich, anchor worms, Hexamita, trichodina, or fish lice are all common threats that affect the fish differently and require different approaches.

Quarantine may be necessary to contain and mitigate the problem if your fish is dealing with parasites.

Skin parasites are easier to treat, as adding tank salt may prove a reliable and easy solution. Internal parasites are trickier since they require a more intricate approach.

Antibiotics may be necessary in this case, depending on the parasite’s type and the infection’s severity.

3. High Metal Concentration

Heavy metals are a concern in closed aquatic systems due to the lack of proper water circulation.

You can mitigate the problem with the help of a reliable filtration system and by performing regular cleaning and maintenance, but you’ll never be completely safe.

Your fish may experience heavy metal poisoning from a variety of sources. The water can get contaminated via new plants, rocks, decorations, or even new tank equipment being submerged into the fish’s habitat.

Heavy metals like lead, cadmium, or mercury have no health or nutritional benefits; they’re simply toxic and can become deadly even in tiny concentrations.

Research has also shown that fish, in general, can absorb heavy metals from their environment quite effectively via their skin, gills, kidney, liver, and intestinal tract. This is why water pollution affects them so much.

Your fish will exhibit a variety of symptoms when experiencing heavy metal poisoning, like red or bleeding gills, skin discoloration or ulcerations, signs of suffocation, lack of appetite, etc.

But the first noticeable changes relate to the fish’s behavior. You will notice the fish exhibiting erratic swimming movements, rubbing against rocks and aquatic decorations, and gasping for air.

I recommend quarantine when that happens. This allows you to separate the fish from a potentially toxic environment and contain and control the disorder.

If you can’t pinpoint the problem, discuss the issue with a vet for professional insight and assistance.

4. Ammonia Burn

Ammonia is considered a pest chemical. This toxic compound is the natural result of organic matter decaying in the water and this one kills fish quickly.

Ammonia is generally not an issue in a well-cycled and well-maintained system, but things aren’t always so simple.

A well-cycled aquarium has billions of nitrifying bacteria breaking down ammonia and turning it into nitrites. These are just as toxic as ammonia, which is where the denitrifying bacteria come in.

These consume nitrites and turn them into nitrates which the fish can tolerate up to 20 ppm.

The problem is that this isn’t a failproof system. Ammonia can spike at times due to insufficient cleaning, a clogged filtration system, dead fish rotting in the tank water, or even outside poisoning in some cases.

You need to take measures fast to prevent severe health complications when that happens.

Ammonia poisoning will kill your fish fast, even in small concentrations. Fortunately, affected fish display a variety of symptoms along the way, such as signs of suffocation, rapid gill movement, lack of appetite, erratic swimming, hiding behavior, etc.

They may also rub against rocks and plants due to the chemical affecting the skin and causing burns and itching.

In severe cases, fish may display bleeding gills and severe body lesions. At this point, death is certain.

You can prevent this issue by:

  • Having a water tester kit available to monitor water quality regularly
  • Having a reliable cleaning routine in place to remove dead organic matter, food residues, fish waste, and dead leaves
  • Installing a good filtration system for mechanical, biological, and chemical cleansing
  • Making sure that the tank is properly cycled
  • Preventing overfeeding and cleaning excess food residues if necessary
  • Investing in a few tank cleaners to consume some of the organic matter that accumulates on the tank substrate
  • Monitoring your fish constantly to detect any health problems in time

Fish can recover from ammonia poisoning, provided that the issue isn’t too advanced already.

If your fish doesn’t show any improvement over 1-2 weeks, consider euthanasia to spare it of further suffering.

5. Water Parameter Changes

Your aquarium water should remain stable in terms of quality and overall parameters, provided you ensure optimal maintenance. But, sometimes, things may not go so smoothly.

Adding new plants or decorations to the water is always an opportunity to affect water parameters, sometimes significantly.

This tends to happen when adding new forms of substrates like crushed coral, which raises the water’s pH.

Another problem comes with performing massive or overly frequent water changes. Water changes are necessary to aerate the water, remove dirt and excess nitrates, and make the water clearer overall.

The problem is that the water change process also dilutes water minerals which fish use during osmosis.

Using tap water is also dangerous due to the high chlorine content, which can kill the fish.

Any significant changes in the water parameters will cause fish to experience stress and exhibit specific behavior along the way. The symptoms that they will exhibit will differ based on the nature of the problem.

Your fish will showcase a lack of appetite, lethargy, laying near the substrate, trying to jump out of the tank, attempting to breathe at the water’s surface, etc.

To prevent the issue, always keep an eye on the water parameters. Some variations are acceptable, but drastic or frequent fluctuations in water quality and parameters will eventually hurt the fish.

As for water changes:

  • Never change more than 15% of the total water volume at once
  • Always use dechlorinated water
  • If you’re using RO/DI water, use a water conditioner to remineralize it before use
  • One water change per week should suffice in most cases
  • As a general rule, smaller tanks require more frequent water changes than larger ones

6. Stress

Yes, fish stress is a real problem with many underlying triggers.

Fish can get stressed for a variety of reasons, such as:

  • Struggling to adapt to their new setting
  • Being forced to live in a barebone system with not enough hiding areas
  • Being forced to live in an environment different vastly than their natural habitat
  • Experiencing health issues due to poor water quality and unstable water parameters
  • Being overfed and experiencing digestive problems
  • Being paired with aggressive, territorial, bullying, or predatorial tankmates
  • Living in an environment with high social tensions, extreme food and reproductive competition, etc.

This may seem overwhelming, but you can fix the problem relatively easily. The solution is to identify what’s stressing the fish and address that problem asap.

All fish display similar behaviors when stressed, which include constant hiding, lack of appetite, lethargy, rubbing against various tank elements, etc.

There are multiple potential solutions to consider, such as:

  • Increasing the tank size – All fish have a given personal space and the instinct to establish territorial boundaries for themselves. This means that your fish will become stressed and aggressive when overcrowded, so consider either upgrading the tank or culling their numbers. How much space a fish needs depends on the species. Guppies, for instance, require approximately 2 gallons of water per fish. An adult Oscar demands around 75 gallons per fish.
  • Adding more hiding areas – It’s always useful to have a lot of live plants, rocks, caves, driftwood, and other aquatic decorations available. These will create a more natural-looking environment and provide the fish with plenty of readily-available hiding areas. This way, the bullied can defuse the situation by running and hiding from their pursuers. Naturally, this isn’t an ideal solution in and of itself. If the fish is constantly in hiding due to aggressive or territorial companions, its mental state will degrade with time. But, at least, it’s a good temporary solution until you figure out a more permanent fix.
  • Removing the aggressor – Not all fish are alike. Some are more aggressive or dominant, despite belonging to a docile and friendly species. So, you need to assess each case differently. If the aggressor is simply untamable, consider removing it from the environment. It’s always more profitable to eliminate one bad apple to protect the rest.

Other potential fixes include offering more food to eliminate food competition, culling the number of fish males since these are more violent overall, etc.

7. Medication

Medication is often necessary to treat viral, fungal, or bacterial infections and other health issues. The problem is that this is a game of precision.

Dose the medication poorly, and the fish will experience adverse effects as a result. Using the wrong medication for the job has a similar outcome.

The most common problem in this sense relates to antibiotics. These are extremely effective at combating viruses and bacteria since that’s what they’re made for.

The problem is that antibiotics do not discriminate between good and bad bacteria; they will eradicate everything.

So, I recommend quarantining the fish into a hospital tank before the treatment and always consult with your vet first.


Fish display many behaviors, and they’re all quite telling of the fish’s mental and physical states.

It all comes down to reading them properly.

Fortunately, you’re now armed with the robust knowledge you need to face any situation with confidence and precision.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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