Ask Jerry: The Oscar (Astronotus ocellaris)

“Oh, he’ so cute. I want one!”  This is usually the first response from new aquarium keepers the first time they see this cute little one inch baby oscar fish, Astronotus ocellatus” so graceful and with such a friendly attitude swimming through the aquarium.

Unfortunately, they don’t understand that this cute little fellow can rapidly grow to over a foot long and weigh over three pounds. They will also eat any of their small tank mates and outgrow any tank less than 50 gallons.

Many people say “I will take them back the place I bought them when they get too large”. Remember that the store may not have room for large fish or just will not accept fish from anyone except suppliers.

The Oscar (Astronotus ocellaris)

Oscar fish are originally from streams in many areas of South America. As babies, they are a very pleasing grey color with white to greenish marbled type lines. As they grow they become a velvety greenish grey in color and develop a very obvious circle at the beginning of the tail fin. Wild specimens are rarely shipped any more due to regulations and excessive shipping cost. They are now mostly pond raised in Florida and Singapore by the many thousands and shipped to suppliers and tropical fish stores all over the world. They are an easy fish to find in most pet and aquarium stores, and not very expensive.
This little fellow, even with all the drawbacks, quickly became one of America’s favorites, next to the small little guppy fish, and probably most talked about aquarium fish creating many fish stories. Through hybridization and selective breeding there are now dozens of colors from albino to beautiful reds, yellows, tigers and many others with short or long fins to choose from.

The Oscar (Astronotus ocellaris)

oscar fish (astronotus ocellatus) swimming underwater
oscar fish (astronotus ocellatus) swimming underwater
Oscars are very easy pet fish to keep. If kept one per tank they make great pets.
Oscar fish are very intelligent and can be trained to do many tricks.
Be careful teaching them to jump or they may miss and end up on the floor. A heavy glass aquarium cover is a must.
Oscars are not picky eaters, large frozen foods, live feeder fish, large pellets and other large formulated dry foods (including any small tank mates).
astronotus ocellatusThey don’t need any special water conditions as long as the parameters are reasonable. As are most large fish, they are messy and need frequent tank cleaning and water changes.
Oscar fish do need a large aquarium, single specimens at least 50 gallons, and usually can be kept to only one per tank because (as are most cichlid fish), because they are very territorial.
If you start with a few very young  specimens, you may be able to get two or more to live together, but not likely unless you have a very large aquarium, 150 gallons or more.
They are not bad tank mates to larger non cichlid fish that they can’t get in their mouth.
If they can get another fish in their mouth, WILL eat them. It  may take a while for them to catch them, but they will. Larger, fast swimming fish such as tinfoil or other large growing barbs, leporinus, anostomus, tri-color sharks and many more are suitable tank mates, but they must be fast swimmers.
If the oscars can catch and corner them they will beat them up.
Usually, after trying for a while they will give up and get along fine.
Oscars are very popular and make great aquarium fish as long as you know what to expect. I watched their popularity grow rapidly as they they began to be commercially raised and available in so many different varieties.
Remember all the negative things you need to prepare for, and if you’re ready, enjoy your new friend!
Dr Erik Johnson is a Marietta, Georgia Veterinarian with a practice in small animal medicine. He graduated from University of Georgia with his Doctorate in 1991. Dr Johnson is the author of several texts on Koi and Pond Fish Health and Disease as well as numerous articles on dog and cat health topics.