Fish Rubbing On Rocks – 6 Top Reasons Why?

If you notice that you have fish rubbing on rocks, gravel, or plants in your aquarium, you may be concerned about whether this is normal behavior or whether they are sick.

Fish will often rub on rocks to clean themselves or simply to scratch an itch. It is often referred to as flashing and is very natural behavior, so don’t be alarmed. If you notice your fish rubbing on rocks more frequently, your fish may have parasites or is stressed because of high ammonia levels in your tank.

If you catch your fish flashing just now and again or more regularly, I have listed 6 of the top reasons why fish like to rub themselves against rocks, which will hopefully help you decide why your fish may display this behavior.

Fish Rubbing On Rocks - Top Reasons Why

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1. Natural Behavior

Most fish flick against rocks or gravel at some time or another. Believe it or not, fish that rub against rocks may be doing so because it is just part of who they are and is completely natural. They may be showing dominance or just flirting with each other, getting ready to mate.

Throughout the animal kingdom, mating rituals and displays of dominance over territory can be quite bizarre. Fish are no different and have limited ways to show what they are thinking or feeling, so they will often display weird or unusual behaviors for the most natural reasons.

An example of this behavior would be African cichlids which can display a wide range of mating behavior. Some African cichlids will spawn on rocks and spend time cleaning the rock beforehand by rubbing against it.

It is always worth researching the particular species of fish that you are concerned about to better understand their natural behavior patterns.

Another natural reason that fish bounce off the bottom of the tank is to uncover food hidden beneath the gravel or sand. As the fish bounce off the bottom, a plume of food particles usually swirls around for your fish to devour.

2. Your Fish May Be Bored

Boredom is another reason why fish will display odd behaviors such as rubbing on rocks or the gravel on the bottom of the tank.

Bored Fish
Don’t let your fish get bored.

Fish can get bored for many reasons such as:

  • Living in an undersized tank.
  • Having little or no company.
  • Living in a tank with no ornaments, rocks or plants.

An undersized tank will give a fish little to no exercise and may lead to pent-up frustration and even obesity. Living in such a confined space would be so far away from how they would live in the wild that the fish may display its frustrations by rubbing against rocks or gravel on the aquarium base.

If a fish has little or no company, it would be like living in solitary confinement. Many fish species are quite social in the wild, and living a solitary life, I’m sure, would drive it to the edge of insanity or beyond.

Boredom and loneliness cannot be good for a fish’s happiness. Many animals, including fish, have had bizarre behaviors noted when kept in captivity that wouldn’t be usual in the wild.

An aquarium with little or no rocks, ornaments, or plants would also be very different from how fish would live in the wild and could lead to boredom. Fish especially like to dart in and out of tubes or arches, often playing with other tank mates.

Fish also like to hide themselves away in dark corners or within the undergrowth as it brings them comfort. Fish in the wild would not be consistently exposed and on show.

All of the reasons listed above can contribute to boredom and, more importantly, how they would live in the wild.

I regularly discuss in my posts how as aquarists, we should be providing the best environment for our fish to live in. By making our aquariums mimic their natural habitats as closely as possible, we will observe the most natural behaviors from our fish and be at their happiest.

Adding some cheap plants will create something much more natural, and it will help in oxygenating your tank. If you add a cheap piece of PVC tubing, you will give your fish somewhere to hide or play.

Just taking a few extra steps can curb a fish’s frustrations or boredom quite easily, and you may notice they will stop certain behaviors like rubbing along rocks.

3. Your Fish Has Parasites

Parasites are common and affected fish may rub themselves on rocks and are of a little more concern. Parasites can cause itching, and the only way for a fish to detach the parasite is to rub itself along a rough surface.

How can you tell if your fish has parasites?

Fish can suffer from both internal and external parasites which will often result in different symptoms.

If you look very carefully, you may notice parasites hanging from the body of your fish, or you may notice missing scales, ulceration to the skin, or white spots.

If your fish are rubbing against rocks or rough surfaces quite regularly, and it is a new behavior, this can also be a sign of parasites.

Parasites are often difficult to spot for beginners, but you will become more accustomed to certain common diseases and how to identify them over your years of being an aquarist.

Aquarium Parasites
Parasites can cause itching to your fish’s scales

Examples of Fish Parasites

A discussion on parasitic infections in fish will take a whole post on its own, but I will list a few of the most common parasites that you may encounter, which will cause itching and discomfort to a fish’s skin.

  • Ichthyophthirius multifiliis (more commonly known as “Ich” or White spot disease) and probably the most common fish parasite, and is easily identifiable by the white spots covering your fish’s body.
  • Chilodonella
  • Trichodina
  • Mongenean trematodes (More commonly referred to as “Flukes“, usually “Gill Flukes” or “Skin Flukes”)
  • Anchor worms
  • Argulus Japonicus (More Commonly referred to as “Fish Lice“)
  • Piscinoodinium
  • Hexamita
  • Ichthyobodo (or “Costia“)
  • Leeches

The list above is not exhaustive as many more known parasites can infect both Marine and Freshwater fish.

It is more important to understand that parasitic infections in fish may cause the rubbing behavior on rocks and other surfaces in a fish’s attempt to remove the parasite.

Parasites can get into your tank by newly introduced fish that are already carrying the parasite. Some people like to start new fish off in a quarantine tank for a few days before introducing them to the main tank.

Parasites will also attach to live plants so the addition of new plants to an aquarium can inadvertently cause a parasitic outbreak. Live plants should always be cleaned and quarantined for 2 weeks before adding to your established tank.

How To Identify Parasites In Fish

Most parasites have easy-to-identify signs to help you find the correct treatment such as the white spots from Ich, but gill flukes (Dactylogyrus) and skin flukes (Gyrodactylus) are microscopic and will often cause secondary infections before you will notice anything is wrong.

If you are unsure if parasitic infection is the problem, you should contact a fish vet for advice.

If fish are becoming unwell for reasons such as poor water quality in your aquarium, parasites can quickly spread through the entire population leaving behind much devastation.

If you are worried about a parasite passing to other fish, you can remove the affected fish and place them in a quarantine tank also known as a hospital tank where fish can receive treatment for the parasite.

Treating Parasites In Fish

There are lots of treatments available from local fish stores such as a salt treatment which would be recommended for many parasites and will often cure Ich. Aquarium salt can be purchased at most pet shops, however, rock salt or kosher salt is also suitable, but you must follow instructions closely when adding any foreign chemical to your tank.

Salt treatments are also good for Gill Flukes and Skin Flukes and if the salt treatment fails, Malachite Green is a very safe treatment for many parasites and fungal infections.

Formalin is another effective treatment for fish parasites but it is not as popular because the active ingredient is formaldehyde which, although highly effective, and safe for fish in very low doses, is known to cause cancer. Fromaline should only be used by trained professionals and in severe circumstances.

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Another way to cure many parasites is to increase the water temperature in your tank. You should increase the temperature to at least 82°F to have any benefit and if your fish can tolerate the increase, a temperature of 86°F is often cure Ich completely.

4. Does Your Fish Have A Fungal Disease

Fungal diseases are more often found on dead fish, although they can be found on fish already in poor health with lowered immunity.

Many people have suffered from a fungal infection in their lifetimes, such as Thrush or Athletes foot, and can testify to how itchy the skin can become.

If your fish is suffering from a fungal infection, it too will be suffering the dreaded itch and will want some much-needed relief by itching itself against any hard or rough surface in the aquarium.

Fungal infections can often look furry and cause the skin to become soft and inflamed.

To stop the infection from returning, you will need to identify why your fish is unwell.

5. Your fish is Stressed

If you have completed a large water change in your fish tank and the newly added water has caused a drastic change to the overall temperature within the tank, it can start a stress response in your fish.

Similarly, if the chemical makeup of newly added water is much different, it can also cause a stress response.

When we talk about stress in fish, we are not talking about money worries or relationship worries. Fish can become stressed with major changes to their environment, such as a drastic change in tank water quality leading to such things as ammonia poisoning caused by high ammonia levels, difficulty breathing or the tank being just too hot.

Water quality problems are a major cause of stress in fish. Ammonia poisoning is often caused by a rise in ph levels which can upset the nitrogen cycle, leading to gill damage and eventually difficulty in breathing.

stressed fish
Your fish may be stressed.

Fish can also become stressed if other fish are bullying them. Bullying often occurs between certain species. It is important to check how compatible your fish is with other species in the tank.

The best fix for stress is figuring out the cause by monitoring other fish in the tank and testing the tank water parameters and quality. Quick water changes are often an easy fix for most problems that may occur.

Increased ammonia levels can be fixed quite easily and keeping your tank well oxygenated and clean will keep ammonia levels down. Water test kits are readily available from fish stores and quickly identify any water quality problems.

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Invest in a good filtration system and change the filter media regularly (at least once a month). Keep water parameters within suggested ranges, perform regular water changes and add a water conditioner at regular intervals. By following these steps, you will know that your fish cannot be stressed due to natural reasons.

6. Your Fish Is Simply Just Itchy

Fish don’t have hands or fingers to scratch, so it makes perfect sense that fish rub themselves against rocks, sand, or other rough areas in their tank. I’ve been known to find a nice rough wall or tree many times so that I can scratch my back against it (Ooooh!! Instant relief….).

Fish scratching themselves will enjoy this feeling of relief as well and is a very natural way to relieve themselves of an itch.

It is wise to make sure the rocks in your tank are not too sharp, as fish flashing against sharp rocks could cause injury. African cichlids are known to be quite aggressive and when these fish bounce off rocks, any sharp edges could cause damage to their skin and scales.

Frequently Asked Questions

Jon O'Connell

I have kept both marine and freshwater fish and set up almost 100 aquariums. Although I am no longer doing it professionally, I hope I can help others to enjoy keeping happy, healthy fish by sharing my many years of experience.

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