Oscar Fish Population and Maintenance

Oscar Fish is not known to exist in the wild in the Northern Territory. However, it is a popular aquarium fish throughout Australia and is considered to have the potential to become a major pest of wet tropical regions of northern Australia. Typically, oscar grows to about 200-280 mm, Young Oscar fish have wavy white and orange markings on a black background; colouration of the body and fins of adults is usually very dark, with olive blue-green and mustard colours, highlighting large dark blotches. Some have orange or red markings.

The base of the caudal fin has a large spot or ocellus bordered with red. Fin colouration varies; usually it is very dark, occasionally there are ocelli present and eyes are red. This species does not tolerate cold waters. A lower lethal temperature of 12.9°C has been reported for specimens under experimental conditions. The natural diet of oscar includes fruit, snails, insects and small fish. Other items such as reptiles may be opportunistically eaten. It is an omnivore with carnivorous tendencies. Oscar Fish is renowned for its aggressiveness. It may have a significant impact on native fishes through direct predation and competition for breeding areas.

Oscars mature early (10 to 12 months), have relatively high fecundity and are territorial during the breeding season. Spawning normally takes place in still waters on flat, solid surfaces. The female typically lays about 3,000 eggs and both parents are occasionally seen guarding hundreds of young in shallow water along shorelines.

DISTRIBUTION

Oscar is a cichlid native to the Amazon basin and has worldwide commercial value as an ornamental species. Over its native range oscar is found in the Amazon, Orinoco and La Plata River systems in South America. Wild populations of oscar are not known to exist in the Northern Territory. However, populations of this exotic fish do exist along the Central Queensland coast and it is considered to have the potential to become a major aquatic pest of wet tropical regions of northern Australia.

Oscar In Aquarium

When selecting filtration for an oscar tank, you will need to keep a few things in mind. First and foremost, you will need to remember that Oscars are very big and very messy creatures, probably messier than any other fish you have kept. They eat a lot, and a lot of what they eat ends up coming out of their gills in a mashed-up mess. The rest comes out the back end as prodigious amounts of feces. Combine that with the relatively large amount of urine produced by Oscars, and you have substantial hurdles for both biological and mechanical filtration.

A second consideration is the size of the tank. If you need help selecting an apropriate sized tank, read this article, and this article. Larger tanks will need more filtration, both to provide adequate water movement, and to ensure that all water in the tank passes through the filtration with a reasonable frequency. A third consideration is your budget. Different types of filters cost varying amounts. However, as we will examine later in this article, the old axim “you get what you pay for” is quite true in fishkeeping.

When I talk about wet/dry filtration, I am talking about sumps that sit under the tank, not the “bio-wheel” filters produced by Marineland. Wet/dry filters are the kings of biological filtration.
They achive this superior biological filtration by running water across massive amounts of biological media in the presence of air. Different designs achieve this in different ways, but the principles involved remain the same. The only drawback of wet/dry filters is that they normally either lack, or are very weak in the area of mechanical filtration.

As mentioned above, mechanical filtration is quite important in an oscar tank. Therefore, if you use a wet/dry set-up, you will need to make sure that mechanical filtration is covered. This can be done by either modifying your wet/dry system to include mechanical filtration directly, or by adding supplemental filters to perform the mechanical filtration role.

Filters
Modern cannisters are the Jacks-of-all-trades of the filtration world. They do this by providing large amounts of space for media that can be customized to fit your specific needs. They can be optimized to provide mainly biological, mainly mechanical, or a good balance between the two. Cannisters are also excellent investments because of their ease of maintenance, and relatively inexpensive operating costs. Properly-sized cannisters can go anywhere from a month to as much as 4 months without any maintenance. Compare this to most other types of filtration, which needs to be serviced at least every couple of weeks, and you can see some substantial savings in bot time, and media costs.

Also called Hang-On-the-Back, or HOB filters, the power filters are by far the cheapest filters to buy. They are an excellent choice for smaller (55 gallons and under) tanks, or as supplemental and/or back-up filtration on a larger tank. While it is theoretically possible to put enough HOB filters on tanks up to about 125 gallons to provide adequate filtration, I do not recommend it. This is because in this size range, you are talking about at least three filtes that will most likely need to be maintained weekly. This is an aweful lot of work and recurring expense for filters that are only marginally adequate.

While it would be difficult to add enough to properly filter a tank with one or more full-grown
oscars, sponge filters do have some good uses in Oscar keeping. They are a cheap way to add
a little extra mechanical and biological filtration to a tank, and make nice back-up filters. Also, if you keep one running in a large tank, you have a pre-cycled filter ready if you need to set-up a hospital tank. Sponge filters are also cheap, effective filters for fry grow-out tanks.

Two factors essentially rule out undergravel filters (uGFs) for oscar tanks. First is the general messiness of Oscars, which is discussed above. The waste tends to clog up the gravel, and reduce the flow through your UGF. Second, Oscars love to dig, especially around spawning time. They dig so much that they will often dig all the way to the bottom of the gravel, and expose the UGF's plates. This will cause a short-circuit in the water flow, and virtually eliminate any filtration occuring in the UGF. When combining these two factors, it is generally best to avoid UGfs in an Oscar tank. While they might provide some benefit as supplemental filtration, the work involved in keeping the gravel clean and the UGF plates covered is simply not worth it.

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