Oscar Fish Aquarium Size

How large do oscar fish grow, and what size aquarium do they need?

Q. I have a 50-gallon aquarium to which I have added two 3-inch oscar fish. I think they will have adequate room to grow. The aquarium is equipped with two powerheads and a power filter on the back. What other types of fish can I put in with my oscars that they won’t eat? Can they be bred? They were sold to me under the name tiger oscar. Anything you can tell about them would be much appreciated.

A. The 50-gallon aquarium you describe is adequate for your oscars at their present size. Oscars, of course, can grow significantly — up to 10 inches in length — and even a 50-gallon aquarium will be too small for two adult fish at that size. If you are serious about keeping these fish on a long-term basis, it would be a good idea to give serious consideration to providing them with more living space at some point down the road, keeping in mind that oscars can grow larger rather more quickly than you might assume.

Right now, there is no reason why you can’t keep them with a fairly wide selection of other fish. Tinfoil barbs, for example, are too large and fast to be considered as possible food items by oscars, and they provide a certain amount of dither activity for the oscars that will keep them active and out in the open.

Dither fish are an important aspect of many cichlid setups. The reason is that the presence of other freshwater fish, particularly schooling fish, swimming about is a sign that all is well, thus encouraging the cichlid fish to stay in the open rather than hide.

You could also try keeping them with some of the less aggressive South American cichlids, such as green severums, blue acaras or juriparis. These fish are, again, too large for the oscars to consider as a potential meal and are not so aggressive that they will cause the oscars trouble at any time later.

I strongly recommend against keeping oscars with any of the larger Central American cichlid fish. These fish tend to be much more aggressive than the oscars and will often give them a hard time.

There is no reason why you cannot breed your oscars, provided that you actually have a pair. This is not the easiest thing in the world to determine. There are no really reliable color differences that allow you to tell male from female.

When your oscars are a bit larger, between 4 and 5 inches, you can remove them from the aquarium, one at a time, turn them over and examine the shape of the genital papillae. This structure comes to a fine point in males and tends to be blunt and wide-mouthed in females. There is a useful diagram showing these differences in my book, The Cichlid Aquarium (Tetra Press), that you might like to consult.

Oscars are not the easiest neotropical cichlid fish to breed even if you have the good fortune to own a male and a female. When they do spawn, they are very prolific. Consequently, you will find yourself having several thousand voracious young to feed. Give some serious thought to both housing and growing the young, as well as disposing of them before committing yourself to the breeding project.

In any event, I see no reason why you can’t look forward to many months of pleasure as you watch your oscars grow and develop the distinctive personality that these highly intelligent cichlid fish often show toward their owners. Just remember that you should be prepared to provide them with larger qurters as they grow.

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