Why Did My Oscar Fish Die? (Find out why!)

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It is unusual for an oscar to suddenly pass away without any signs. They are generally strong, hardy fish that can battle through most situations given half a chance. However, occasionally things can just work against your oscar and he isn’t able to keep going. Below we look at some of the commonest reasons Oscars pass away suddenly.

Oscars have bundles of personality. They quickly become pets, even members of the family. If your Oscar dies, especially if the death is sudden or unexplained, it can leave you wondering if you did something wrong or whether there was something you could have done differently to save your oscar.

I have been keeping, breeding, and showing Oscars for the best part of 30 years. During that time dozens of Oscars have passed through my fish room. I currently have a trio of Lemon Oscars in a 180 gallon (680 liters) aquarium.

Why Did My Oscar Die Shortly After I Got Him?

Oscars are sold by their millions worldwide. They are one of the world’s most popular fish. Speak to any fish keeper that has been in the hobby for more than a couple of years, and the chances are they have or had an oscar.

The problem with such a popular fish is they are produced in huge quantities, shipped around the world with dozens, maybe hundreds squeezed into each bag, and then placed in a sales tank at the fish store where they may only sit for a few days before being brought home to your new aquarium.

This whole process can be extremely stressful on a 2” oscar. Stress is a massive killer. It seriously compromises their immune system.

To reduce the chances of stress putting an early end to your Oscars life, make sure your tank is ready for him. When you get home with your new fish, place the bag on the top of the tank to float for around 20 minutes.

This will allow the water in the bag to get to a similar temperature as the water in the tank.

When you’re ready to release your oscar, pour the bag of water through a net into a bucket, catching the oscar in the process. Carefully release him into his new tank. I usually leave the lights off for the first 24 hours and certainly don’t feed him until the next day.

Providing your oscar with a good hiding place, like a terracotta pot on its side, will give him somewhere to hide until he feels comfortable.

Why Did My Oscar Die After Only A Week?

So, you get your oscar home and everything seems rosy. He is swimming around the tank happy as can be, then, without warning he dies. This sudden death in a new tank can often be attributed to an ammonia spike.

When fish go to the bathroom, their waste contains ammonia. The job of the aquarium filter is to process this ammonia to the less harmful nitrite and then to the less harmful still nitrate. To do this, filters use bacteria.

The bacteria can process the waste quickly. The problem is, it takes time for the bacteria to build up. They will colonize every inch of your filters’ media if given enough time.

With a traditional community tank that will house dozens of small fish, we try to start off slowly. Maybe add 5 fish, then leave them to live in the tank for 3 or 4 weeks, then add another 5 fish, and so on.

This way the bacteria in the tank gets a chance to build up as the number of fish increases.

The problem with an oscar is they eat lots and poop lots. A brand new filter may struggle to process the waste before the ammonia builds up to toxic levels.

To combat an ammonia spike there are two routes to take. The ideal route is to set your new tank up and then leave it to run, without any fish, for 6 to 8 weeks. Every couple of days, add a small pinch of fish food.

This food will break down and create ammonia, which in turn will allow bacteria to build up in your filter. After 6 to 8 weeks your tank will be ‘cycled’ and you can add a small oscar.

Be aware, this method won’t work if you add 3 full-grown Oscars and start chucking the food in with them. The ammonia will still spike as the filter isn’t used to that much waste.

An alternative to cycling over 8 weeks is to add your fish to his new tank, and then carry out large water changes every other day for 4 to 6 weeks until your filter has a chance to build up sufficient bacteria to deal with your Oscars waste.

If you choose this method, never skip a water change. It could be fatal for your fish.

Whichever method you choose, use a good aquarium water test kit to measure your ammonia levels. I have had great success with the Master Test Kit from API. I have always found they are reasonably priced on Amazon (you can check the current price HERE).

Why Did My Oscar Die After A Few Months?

If you’ve had your oscar living with you for a number of months, and then he passed away, it can be difficult to determine why.

Assuming there were no obvious signs of illness (such as white spots over his body, a fungus growing on him, or a hole in his forehead), and assuming you’ve been checking your water quality regularly using the API test kit to make sure your ammonia didn’t spike unexpectedly, my first thought would run to internal parasites.

When fish are imported into the country, there is a good chance they will pick up internal parasites, such as tapeworms, on their journey. Fish imported from the wild almost always come in with tapeworms.

I highly recommend that any fish that comes into your possession, whatever the source, is treated for internal tapeworms.

Tapeworms live inside your fishes’ internal digestive system where they rob the fish of the nutrients from the food he is eating. Over time your oscar will become weaker. His immune system will struggle to fight off bacteria and infections. A fish can be so heavily infested that it stops eating altogether.

To de-worm my Oscars, I use Paracleanse from Fritz (you can check the current price on Amazon). Follow the instructions on the packet to the letter and consider treating more than once, over a period of a few weeks as the treatment only kills the tapeworm in the worm stage of its life, not the egg stage, meaning the eggs can survive treatment and re-infect your oscar.

In Conclusion

There could be countless reasons where your oscar passed away. To give your oscar the best possible chance in your care, follow the basic principles of feeding good quality food little and often, testing the water with your test kit, and changing water as necessary. When you see signs of illness, treat quickly with a good quality aquatic medication.

Hopefully, your oscar will give you many years of enjoyment. They make excellent ‘wet pets’.

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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