Oscars: Aquarium Size and Filters

What size aquarium and what type of filters work best for messy oscars?

Q. I have a 48-gallon aquarium and I’d like to keep a couple of oscars. Would the 48-gallon be big enough for two oscar cichlids or should I get a larger aquarium? Also, I understand oscars are considered messy, so what would be the best type of filter to use?
Garrett Holdsby
Tallahassee, Florida

A. As you probably know, oscars (genus Astronotus) routinely grow to more than 10 inches total length (which includes the tail) in captive situations, and because of that, the recommended minimum size aquarium for a single specimen is 55 gallons. Of course, in the case of oscars, the old adage of “bigger is better” definitely applies. Therefore, I suggest a larger aquarium before you invest in some oscars. Ideally, consider your budget and the amount of floor space you have available for the effort and based on those two considerations, buy the largest fish aquarium you can – a 100- to 200-gallon aquarium would not be overdoing it by any means.

You’re right about oscars being messy, but it is because they have prodigious appetites willingly placated by easily manipulated aquarists. Anyone who has kept oscars knows all too well that they are more than capable of behaviorally manipulating their owners. A wiggling, wide-eyed oscar is perhaps the aquatic equivalent of a puppy dog – and who can resist that? So, as a result, oscars in a captive situation tend to get fed far more fish food than they need. While that results in a lot of fish waste, it can also lead to fish health problems (such as intestinal blockages and hepatic lipidosis) or fatty liver disease.

Given that even properly fed oscars generate their fair share of wastes, I suggest you use an aquarium filter you can easily and quickly clean. If you end up using an aquarium filter that is difficult or time-consuming to maintain, you’ll likely not clean it as often as you should. I find the hang-on-the-back power filters the most suitable for use with cichlid fish that produce a lot of wastes, largely because they are easy and quick to clean – simply take off the lid, pull out the filter media, rinse it and return it to the aquarium filter and you’re done.

Another great aspect of power filters is that you can use as many as you need to get the amount of aquarium filtration you require. On the packaging, most manufactures make a recommendation as to the size of aquarium for which the aquarium filter would be appropriate. However, the manufacturers do not temper the recommendation based on the fact that you intend to keep oscars, so following those recommendations can lead to an under-filtered aquarium. I would suggest you purchase a power filter rated for an aquarium 50 to 100 percent larger than the aquarium you intend to use it on, or double up on the number of aquarium filters to arrive at a similar capacity. With oscars, there is almost no such thing as too much filtration.

Last, no aquarium filtration system is complete without a schedule of regular water changes. With oscars, there’s likely no way to change too much water, so consider changing at least 30 percent to 50 percent every 3 to 5 days. In a large aquarium with good filtration and few fish that schedule can be stretched out a little, but be warned: One of the leading causes of illness with captive oscars is the failure to provide adequate water quality. Big aquariums, big filters and big water changes are the keys to success with Oscars. Good luck!

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