The oscar (Astronotus ocellatus) is a very popular fish in the aquarium hobby, but it isn’t a beginner’s fish, nor is it suitable for the casual fish keeper. Oscars are both very large (as much as 18-inches and 3.5 pounds) and extremely messy fish requiring both large capacity tanks and diligent water management. Furthermore, they require a very warm tank—between 75–81° F (24–27° C) which means you’ll need a good water heater.
Scientific Name: Astronotus ocellatus
Size: 18 inches
Temperature: 75 to 81 degrees Fahrenheit
Origin: South America, primarily the Amazon river basin, Orinoco, Uruguay, and Paraguay
A native of the Amazon basin, the oscar is a cichlid that is considered a human food source in much of its wild range, which includes much of the Amazon basin in parts of French Guiana, Brazil, Ecuador, Colombia, and Peru. Introduced populations reportedly exist in Florida, Australia, and China.
Naming for the oscar has been somewhat complex, it was originally given the seafaring genus classification Lobotes. There are numerous common names including “peacock cichlid” but this is often confused with the many “peacock” varieties of Aulonocara species from Africa’s Lake Malawi. Adding to the confusion is that many of the oscar’s related South American cichlids are also called peacock cichlids.
Coloration in the wild is typically a dark brown with the occasional yellow-rimmed circular marking. Juveniles are typically lighter colored and are often speckled. The species is capable of altering its coloration both to blend into its habitat and for the purpose of ritualized territorial combat. In the aquarium trade, coloration can vary from near solid black to a very pale cream color with varying amounts of speckling and even high-contrast mottling. Red, and red-striped varieties are often sold as tiger oscars. Heavily finned varieties have also been developed.
Like most cichlids, the oscar tends it eggs (presumably in the wild, but dependably when in captivity). Sexual maturation is at approximately 1 year and they can breed for slightly more than a decade. Parents will both clear a flat space in the substrate to harbor eggs and both will participate in brood tending.
Again, as with most cichlids, oscar are extremely territorial. A mating pair will tolerate each other, but typically it works best if the pair are introduced to a new tank at the same time. With sufficient space, more oscar can cohabitate, but it almost never works to introduce a new oscar into an existing population.
For a single fish, you’ll need at least a 40 gallon tank. For each additional fish, you’ll need another 30 gallons or so. Because they are so territorial, they highly prefer an abundance of cover and hiding space, some guides call for as much as 75% of your oscar habitat to be sheltered. Although rarely growing beyond 16-inches in an aquarium, these are big, powerful fish and they spend much time rearranging their territories. You’ll want to ensure that everything you want to remain in a set place is very securely placed and that hard angles and jagged surfaces are minimized as oscars are extremely stubborn and have been known to injure themselves moving objects within their territory.
In addition to a large aquarium with an efficient heater (multiple heaters are highly recommended), you’ll need a very strong filtration system (again, multiples are highly recommended). As noted earlier, oscars are messy fish. They may be messy, but they do not cope with their messes well. Their native habitat is semi-sheltered areas within slow white-water rivers where “housekeeping” is taken care of by the current. To minimize cleaning tasks, it is recommended that you feed your oscar only once a day and feed it slowly. When they no longer take food within 2 minutes, you are done feeding.
Beyond a strong filtration system, you’ll need to cycle approximately 15-20% of the water weekly to keep your fish healthy. Monitoring the temperature is also critical, oscars are highly susceptible to a variety of stress-related diseases when either held at prolonged periods of overly warm temperatures or even brief periods at temperatures below 70°F.
Primarily a carnivore, an oscar is not a very picky eater and have been known to feed on practically anything that falls into the tank. In the wild, they prefer smaller fish, insects, and will even eat fruit when facing a shortage of vitamin C, which they require. They will even try and nip the fins of other cohabiting fish including pirahna. Most high-protein commercial fish food for carnivorous species will suffice. They will also eat feeder fish, but goldfish especially are not recommended as they carry diseases and offer little nutritional value. The oscar diet should be very lean so foods such as poultry and beefheart should be avoided.
Finding suitable tank mates for oscars can be a challenge. Aside from the temperature and territorial behavior issues, an oscar will harass timid species (even if they stay out of the fish’s territory) and will engage with aggressive fish, even when severely outsized which leads to stress and injury. Medium-sized Pacu, which are similar to the piranha in the oscar’s native habitat, can coexist, as can many other south American varieties of cichlids. However, most people find that oscars fare best when alone. Anytime you decide to add fish, another oscar, a Pacu, or other cichlids, you will want to put them all in a new tank all at once to minimize the territorial aggression of the fish.
With an average aquarium-based life of between 8 and 12 years, the oscar can be a wonderful and spectacular companion fish. It may not get along with other fish too well, but with diligent care, it can be the star of your tank.