Why Do Oscar Fish Shake? (With Essential Warning Signs)

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Oscar fish are fascinating creatures. Watching their appearance and behavior was among the reasons I chose to raise them. However, once in a while, I noticed an exceptional phenomenon. I saw that my Oscars shake their body and tail quite frequently. That got me curious, so I began to research the topic a bit deeper. 

Oscar fish typically shake their body and tails as part of a courting procedure, which may also be accompanied by lip-locking. However, persistent shivering among Oscars could also be a sign of infection, or when the fish are experiencing ongoing stress.

As we move forward in this article, I will show you how to determine whether your Oscars are breeding, or possibly experiencing ongoing stress. Following this guide will ensure your Oscars remain healthy and enjoy their ideal water requirements.

Also Read: Stress In Oscar Fish

Why Do Oscars Shake Their Tails?

Cichlids are simple creatures, although their habits are somewhat complicated. It isn’t always easy to diagnose the meaning behind some of their actions. Take their shaking as an example. As you may have already noticed, it can take various forms.

Sometimes they will simply swish from side to side. Other times, they will appear to vibrate or shiver. Most people call it shimmying. This behavior can mean mating, aggression, or a reaction to entirely separate stimuli. 

This is why you can’t ignore it. The same behavior that displays flirtation in one instance could symbolize violence and aggression in another.[1] This applies to Oscars, as they belong to the cichlids family. In fact, you have more to worry about where Oscars are concerned since they are relatively large.

Their dimensions naturally make them strong enough to kill their tank mates. Hence, if their shimmying is a prelude to violence, you need to know that beforehand so that you can take countermeasures. 

Try to keep the following in mind where shaking in Oscars is concerned:

1. Breeding Behavior

An Oscar fish shaking its entire body is probably looking to mate with another fish.[2] Most of the time, those that are ready to mate will accompany the shaking with additional signs such as lip-locking. However, it isn’t always easy to differentiate between mating and fighting among Oscar fish.

It isn’t just the shaking that is difficult to interpret. Various actions in Oscar fish that symbolize mating are also present when they fight. That includes the locking of jaws. Even more problematic are those Oscars that tend to transition from mating to fighting.

That is to say; some Oscars are very violent breeders. Some of them will start chasing one another around. But others will nip and bite each other, going so far as to remove strips of flesh from one another’s bodies.[3] If such violent behavior persists, the Oscars in question are more than capable of killing one another.

And yet, such behavior also falls under the umbrella of mating. If you cannot tell whether your fish are fighting or mating, talk to an experienced aquarist. You may also consult the store from where you acquired your fish. Even professionals confuse this behavior in Oscars.

If you don’t have a professional nearby, your next best choice is to observe your fish for extended periods carefully. Look for signs of violence, such as ripped fins or scars. A bullied Oscar will also turn lethargic, and show less interest in food.

2. Infection

When is shaking normal and when is it a source of concern? Well, this should be your first consideration. Is it normal for Oscars to shake? Yes, it is. Oscars can shake for any number of reasons, as I will elaborate later on.  

However, that shaking is not long-lasting. It should only happen every so often and for short periods. If that is all you have observed, you have nothing to worry about. The shaking only becomes a problem if it persists.[4]

In such cases, you have to consider the possibility that the Oscar fish can no longer control its nerves and muscles. This could be a symptom of a disease or infection from a parasite.[5] The next wise step in this situation would be seeing a vet or a professional.

Also Read: 17 Oscar Fish Diseases

3. Territory Establishment

Oscars are territorial creatures. This is part of the reason why some people prefer to keep them singly.[6] Oscars in large numbers can terrorize your entire tank, intentionally or unintentionally. If your Oscar fish keeps shaking its tail, it is appropriately reacting to a perceived threat to its territorial integrity.

This could be another fish or, for instance, a human hand. It is no different from a cat hissing to repel an unwanted entity in its vicinity. It shouldn’t concern you unless the cause of the aggression is another fish that has continued to trespass upon your Oscar’s territory. 

In such cases, the Oscar might take violent action against the trespasser. That could pose an issue because most fish do not stand a chance against the gigantic Oscar fish. However, if your Oscar is merely reacting to your appearance, you have little to worry about.

4. Stress-Related Behavior

Shaking in fish can sometimes signify distress. The sources of it may vary. Some fish will shake because they feel threatened. This can happen in situations where their tank is filled with larger, more aggressive species that have developed a penchant for bullying them. 

It can also happen in situations where the water parameters are less than ideal. For instance, if the water is too soft or acidic, if the temperatures are too low, or if the concentration of toxins has risen. 

Those are the ideal water parameters you should provide to your Oscar fish:

  • Water temperature: 75-80 degrees F
  • pH: 6-8
  • Water Hardness: 12dH – 15dH

Oscars that are stressed as a result of a threat in the water spend a lot of time hiding. They also won’t eat as much. Also, some fish could suffer from stress simply because they were not appropriately acclimated before you added them to a tank. 

If you can’t identify the exact source of the shaking, start by eliminating the potential causes. Test your water to ensure that the temperature and pH are perfect. Test for toxins as well. Lastly, perform water changes where necessary.

To do that, I highly recommend that you check the API Reef Master Test Kit (link to Marine Depot). For a relatively low price, that bundle will help you to measure your water parameters quite accurately (including pH, nitrites, nitrates, and ammonia).

Also, make sure that your heating and filtration systems are working correctly. Measure your water temperature and ensure that it is adjusted to Oscars. Then, take a while to clean up the tank by removing all waste, uneaten food, and dead plants you can find. 

If your Oscar is still shaking, remove all potential mates to eliminate the possibility of breeding. Keep subtracting the possible causes until you identify the source of the shimmying. If it isn’t for mating purposes, you should definitely take action.

Also Read: Why Is My Oscar Fish Swimming Erratically?

How Do I Know if My Oscars Are Mating?

You can know that your Oscars are mating by scrutinizing their behavior. A mating couple typically becomes more aggressive, presenting gestures such as jaw locking and nipping. Also, the female’s ovipositor will begin to descend, and the couple will seek a spot for eggs deposition.

Oscar fish are not the most subtle creatures. As such, once they are ready to mate, you cannot fail to see the signs. However, keep in mind that they will present those only when fully sexually matured (about 14 months of age):

1. Look For the Typical Aggression

Oscars have somewhat violent mating rituals. When a female is ready to mate, it will test the male’s strength through a show of aggression.[7] They will chase each other around, eventually locking jaws and dragging one another all over the tank. 

You should also expect some shaking, nipping, biting, tail-slapping, and gill flaring, not to mention the spreading of fins. If your male and female Oscars have been showing this behavior for an extended period, there is a high chance for breeding.

2. Observe the Breeding Ground

Oscars lay their eggs on flat surfaces. If you can provide them a flat piece of stone, the Oscars will locate it and clean it with their mouths. Yes, the shaking, jaw-locking, nipping, and biting could symbolize ordinary aquarium violence. 

However, once your Oscars start preparing a breeding ground, you can conclude that their aggression is a sign of mating. You will be more sure once you notice the yellowish eggs appearing on the breeding surface. That is when the male will begin his fertilization.

3. Observe Their Appearance

You can also look at the bodies of your Oscars for confirmation. A female Oscar’s ovipositor will descend once spawning is near.[8] The male Oscar’s breeding tube will extend soon after. Once you observe these signs, spawning should occur in 48 hours. 

You should also keep an eye on their colors. They tend to intensify as well during this period. Once you observe these signs, I encourage you to isolate your Oscars. As they are starting to mate, their behavior will become more and more aggressive.

Also Read: Why Is My Oscar Fish Turning Black?

How Do I Know if My Oscar Fish is Dying?

You can tell that your Oscar fish is dying if it presents typical warning signs, such as loss of appetite and lethargic behavior. Also, the colors of a dying Oscar will gradually fade, and its awareness of the surroundings will begin to deteriorate. 

Oscars rarely die abruptly. However, if they have contracted a fatal ailment, they won’t necessarily tell you. But you can tell by merely looking at their behavior and observing their bodies for the right signs, which include the following:

1. Loss of Appetite

Most fish that are dying lose their appetite.[9] This is true for most living creatures. Like most fish, Oscars will respond by enthusiasm once you introduce food to their tank. This is one way of determining whether or not they are healthy. They will swim in the direction of the food. 

However, if your Oscar shows no interest in its food during meal times, you have every reason to worry. If you keep finding their food in the tank, uneaten, something has gone wrong. Even a healthy fish will die if it stops eating. A sick one cannot afford to skip its meals.

2. Faded Color

Oscars are beautiful fish with bright colors. Those colors can either change or fade for several reasons. One of these is the presence of an illness. If your Oscar’s change in color is accompanied by other signs such as a loss of appetite, you can conclude that its health has deteriorated. 

However, you should first make sure that your Oscars aren’t exiting their mating period. Since, during the breeding process, their colors are getting stronger, they naturally start to fade afterward. 

3. Lack of Awareness

Fish are relatively intelligent. They have a certain amount of awareness, at least as far as their surroundings are concerned. This is why they react to stimuli, such as the presence of food or a tapping hand.

If your Oscar shows no signs of awareness, if it does not respond to any of the standard stimuli, it is probably struggling with a disease that deserves your attention. Some illnesses will compromise your Oscar’s ability to swim properly. 

4. Increasing Lethargy

Oscars that are suffering under the weight of disease tend to become inactive. They either swim slowly or not at all, choosing to hover in place. Their response to every stimulus is lethargic. This is one of the most common signs of illness in fish. 

Lethargy tells you that your Oscar is suffering considerably. Some Oscars will simply lay on their sides. Others will choose to hover at the top of the tank. Both cases mean that something is going wrong with your Oscar. 

5. Air Gasping

You can’t measure an Oscar fish’s breathing with a stethoscope. But you can tell whether or not a fish is struggling to breathe. It will gasp for breath by rapidly opening and closing its mouth. You can also count the number of times the gill covers move. 

Some fish will swim to the top in the hopes of finding more oxygen. This will help if their labored breathing is the result of an oxygen deficiency in the tank. However, it won’t help if the Oscar is suffocating as a result of an internal problem. 

  • If you’ve noticed any of the signs above, make sure to adjust the desired water parameters for that particular species. In case that didn’t help, you should consult a fish vet.  


As was mentioned earlier, Oscar fish tend to shake and shiver during their mating period. As proof, you will notice that the couple is seeking a spot for eggs deposition. However, in some cases, the shakes could mean troubles.

The second case typically comes along with other symptoms, such as a sluggish behavior and lack of appetite. These signs mean you should take action. Start by optimizing their water conditions. If that hadn’t worked, you should seek professional advice.


  1. https://web.mit.edu/lxs/www/cichlids/behavior.html
  2. https://www.cuteness.com/article/signs-breeding-oscar-fish
  3. https://www.fishxperts.com/oscar-fish-care/
  4. https://petcentral.chewy.com/overcoming-the-shimmies-in-tropical-fish/
  5. http://howfishbehave.ca/pdf/how%20do%20parasites%20affect%20fish.pdf
  6. https://aquagoodness.com/oscar-fish-behavior-and-intelligence/
  7. https://www.oscarfishlover.com/breeding-oscar-fish/
  8. https://petcentral.chewy.com/oscar-fish-breeding/
  9. https://petcentral.chewy.com/how-to-spot-signs-of-distress-in-your-fish-before-its-too-late/