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Why does my tropical fish rub itself on rocks and substrate

This is one of the most commonly asked questions among African Cichlid keepers. Chances are sooner or later you will observe your cichlids rubbing themselves on objects and substrate in the aquarium (also known as flashing). Below I will attempt to answer the question above by exploring different reasons as to why that is.

This article relates directly to African Cichlids who are known to rub themselves on rocks, decorations and the substrate in the aquarium, for other tropical fish rubbing themselves please read on as some of the points raised here may go a long way to answering the above question.

Firstly it is important to say that this is not necessarily a cause for concern, however depending on other factors there could be an underlying issue with your fish. This behavior to some extent makes up part of their natural character and should be disregarded as nature.

Rubbing on objects and rocks:

Cichlids “scratch” themselves on rocks and other objects in a motion which sees the fish bounce off in controlled way and thus not harming itself. This is completely natural and the fish may have had an itch. Although natural this can obviously be a dangerous situation as if you have sharp rocks or objects in your set up the fish can injure itself and/or lose some scales which although may not be fatal they will cause significant stress on the fish. Most African cichlids due to their aggressive nature are rather good at healing so with some care your fish will eventually recover.

Rubbing on the substrate/sand:

Another interested behaviour observed in African Cichlids is when they rub themselves on the substrate/sand. This is more common in Haps and Peacocks from what I have observed due to Mbuna being vegetarian and primarily feeding on algae off rocks in the wild. Haps and Peacocks often disturb the sand by bouncing off it in order to release any food particles that may be trapped there. I have observed many times one fish flashing off the bottom and another fish following in it’s cloud of sand looking for food.

Species such as Fossorochromis Rostratus even sift through the sand and filter feed as they would in the wild. They may also be scratching themselves as stated above. 

When is it a cause for concern?

As discussed above this behavior is natural in African Cichlids as long as they are not injuring themselves, don’t have any visible signs of parasites such as Ick (white spots) and are not constantly doing it. If you observe any of these extra symptoms on your fish then you need to consider a course of action. Your fish may be suffering from a form of external parasite like Ick, in which case they will constantly rub themselves on anything they can find, if this continues it will eventually be fatal, if you see visible signs of external parasites or injury it is important to either re-locate the fish to a hospital tank or preferably treat the entire aquarium with the appropriate medication.

Unfortunately parasites are extremely contagious so if one fish has it chances are all your fish do, which really signifies the need for a quarantine tank before adding fish to your main set up. Usually if the cure process is started fast enough the fish will recover. Keeping up with maintenance and providing the correct parameters for your fish helps keep them strong and healthy.


Observing your fish for periods throughout the day will help you understand their behavior and spot anything out of the ordinary such as constant flashing and/or signs of illness. This can be difficult however with everyday life taking over! If you see something out of the ordinary don’t wait, research the symptoms and see if you should be worried or not.