Why Is My Oscar Laying On His Side On The Bottom Of The Tank?

You look into your beloved Oscars tank and see him lying on his side on the bottom. You naturally think the worst. Before you go into panic mode, just take a minute. The majority of the time it’s nothing serious. For fish, Oscars are surprisingly intelligent. They can even get in a mood if you upset them. The chances are it isn’t anything serious.

Eating Daphnia
Eating Daphnia

Over the last 30 years, I think I have kept just about every color strain of Oscar there is. I currently keep a trio of Lemon Oscars in a 180 gallon (600 liters) aquarium. It is a tank full of color, movement, and personality.

Why Do Oscars Lay On Their Sides?

Oscars are real characters. Each one will have a slightly different personality from the next. That’s why so many people love them. They become real wet pets.

One of the reasons an oscar lays on his side is because it is being submissive. Perhaps another fish in the tank is bullying him. Try to observe your tank without the fish knowing you’re there. See how they interact with one another.

If another fish in the tank is pinning the oscar down or constantly pecking at him, he will become stressed and may turn off color and try to avoid the bully fish. If there are more fish in the tank than there are available territories, it may be that your oscar feels defeated.

Sometimes rearranging the rocks and decorations will reset the territories and your oscar will find one for himself.



If after studying the tank you don’t see any signs of bullying or aggressive behavior towards your oscar, maybe your tank’s water parameters have gone wrong somehow. Oscars eat a lot of food and then in turn produce a lot of waste. It is easy for the ammonia to spike or the nitrates to creep up to a level that stresses your Oscar.

Use an aquarium water test kit to carry out a quick check. I use the Master Kit from API. It is very reasonable on Amazon (check the current price). If you find the parameters are off, carry out a large water change (maybe 50%-75%) and then retest. Continue until your parameters are back where they should be.

Ironically, changing water itself can cause an oscar to decide he is going to lay on the bottom of the tank. Don’t worry, he’ll snap out of it soon enough.



Can I Change Water Without My Oscar Getting In A Mood?

Unfortunately, like some people, some Oscars are easily upset. You can try siphoning off a small quantity of water, then topping it up, then siphoning off a bit more, until you’ve changed a fair quantity.

In practice, this is probably more stressful to the fish than just getting the change done. I’ve never had an oscar that held a grudge for long after a water change.

To minimize the stress, try providing your oscar with somewhere safe to hide. A sturdy pile of rocks he can’t knock over or a large terracotta pot laying on its side will give your oscar somewhere to retreat to when he feels the need.

It will also give him a place to defend, giving him something to do whilst you are water changing.



What If Something Is Wrong With My Oscar?

So what do you do if your oscar isn’t just upset, but there is something wrong with him? Firstly, try to establish what might be wrong. Take some time to sit and look at your oscar. Can you see signs of disease? Typically, this will show as white spots (ich) or a white fungus.

When you look at your Oscars head or down his body, are there any signs of Hole in the Head (HITH)? This will show as one or more small pits in his forehead or down his lateral line (the central line running down the middle of his body)? If left untreated HITH can be terminal, killing your oscar.

If there are no obvious external issues, could your oscar have internal parasites such as tapeworms? Whilst you can’t see them from the outside, does his belly look swollen?

If your oscar is new to you, there is a chance he has picked up tapeworms from the store or the wholesaler. Wild-caught Oscars very often come into the country with tapeworms.

Camallanus Red Worms are known to infect a number of freshwater fish. They are especially prevalent in livebearers. Look at your Oscars vent. If he has red worms wriggling from his anus, it is almost certainly Camallanus Red Worms. A fish de-wormer will usually fix the problem. I have had good luck with Paracleanse from Fritz. I usually just order it from Amazon as that is the cheapest place I have found it.

Selecting the right treatment for the illness, and treating quickly will usually sort most fish

problems out. Always follow the manufacturer’s guidance.

In Conclusion

Before you do anything about your Oscar laying on his side on the bottom of the tank, take a few minutes to have a good look at him. Look how the other fish are interacting with him. See if there are any signs of illness. Give him a few hours to see if he snaps out of it. Maybe you just have a moody Oscar!


About the Author

I’ve been keeping, breeding, and showing tropical fish for nearly 30 years. Over that time I’ve done it all! I’ve had great success and I’ve made some really foolish mistakes (like the time I bought an Asain Walking Catfish). Read more…
Richard James
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