Astronotus Ocellatus Species Profile

Astronotus ocellatus

Last updated on July 3rd, 2022 at 10:11 pm

The Astronotus ocellatus, more commonly known as the Oscar Cichlid, comes from Mexico and Guatemala in the Central American river basin and can grow to over 14 (36 cm) inches in length. This makes it one of the largest of all freshwater fish species available to aquarists. Despite its relatively large size, this fish has been kept by hobbyists since it was first described in 1852 due to its attractive appearance and temperament in captivity.

Astronotus ocellatus is a stunning Oscar cichlid native to the Amazon river basin in South America, including the lower parts of the Tocantins, Tapajós, Xingu, Amazon rivers and their tributaries, as well as lakes such as the Palcazu lake in central Brazil.

Astronotus ocellatus (commonly known as the Oscar Cichlid) are large, showy cichlids that are easily identified by their unique red and blue patches along the lower edge of their gill cover and their bright orange to yellow dorsal fin spines.

Astronotus ocellatus overview

Astronotus ocellatus is a large, attractive species of cichlid native to South America that is popular in home aquariums. It is a hardy species that is easy to keep but can be aggressive toward its own kind, as well as other tankmates. This species can grow up to 14 inches in length. Males tend to be larger than females with long fins and bright coloration. Females are less colorful and smaller than males but will show their breeding colors during the breeding season.

In an aquarium environment, live foods such as worms or daphnia should form a substantial part of their diet, supplemented by regular feedings with pellets and flakes which should contain high levels of protein. Vegetable matter such as spirulina algae and blanched vegetables may also form part of their diet. Be careful not to overfeed them though; they are prone to bloating when given an excess of food.

Origin and descriptions

Astronotus ocellatus

The Oscar originates from Rio Xingu in Brazil, where it lives in small creeks, often with substrates of fine sand. The species was formerly named Astronotus ocellatus but was reclassified to Astronotus ocellatus by Kullander et al. in 1988 due to similar morphological features between it and other species within its genus.

In 1991, Mannucci suggested that there were two subspecies of Astronotus ocellatus; one which is found south-eastwards throughout Southern Mexico, Guatemala, and Belize; while a second subspecies is only found northwards through Venezuela up into Guyana and Northern Brazil, which he named Astronotus ocellatus fischeri.

Lemon Oscar Care And Species Profile

Species profile

Astronotus ocellatus- Oscar Cichlids

The Oscar cichlid is an aggressive fish that requires a large tank. It can be kept with smaller tank mates if its aquarium is sufficiently large. This fish will eat any small fish or invertebrates it can fit in its mouth.

It should not be kept with small tetras, dwarfs livebearers, rasboras, guppies, bettas, neon tetras, etc because they are too easily attacked and eaten by an adult Astronotus ocellatus. Avoid keeping with fish less than 1/2 inch as well as long-finned fish such as angelfish and gouramis, who may become entangled in their long fins.

Although Oscars are more tolerant of cooler water temperatures than many other cichlids, they do best at 75 to 80°F (24 to 27°C). Lower temperatures reduce activity levels and prolonged exposure to 65°F (18°C) may result in sickness.

Oscar Fish Appearance

The body shape is very deep, compressed laterally; with a dorsal fin that has a longer base than other cichlids. Their bodies are covered with dark spots along their flanks, which may be red or blue. Adult Oscars have 13-15 dorsal spines, 2 anal spines, 14-16 dorsal soft rays, and 10 anal soft rays; they also have 11 pectoral rays.


Astronotus ocellatus prefers cooler water than many cichlids, and can handle a range of 74-79 degrees F. Their preferred temperature is in that mid-range. Water movement does not appear to be as important for them as it is for some other Oscar varieties, but they seem to do best when there are at least moderate currents.

Tanks should have lots of rocks and wood pieces for cover, and plants will help keep biofiltration healthy. This species enjoys dense cover like Java ferns or Anubias species; you’ll probably want at least one piece per 10 gallons if you want to keep your tank densely planted – it’s an Oscar after all!

Oscar fish size and weight

Oscar cichlid can grow to a maximum height of 14 inches (36 cm) in length and a large adult can weigh up to 1.6 kg

Oscar fish tank size

The minimum recommended tank size is 55 gallons, larger is better.

Tank set up

Astronotus ocellatus live in a temperature range of 25 to 27.5 °C, with a pH of 6.0 to 7.5, and they prefer soft, slightly acidic water that has a low nitrate level; dH should be between 5 and 15. Oscars are generally very easy to care for as long as their habitat is set up properly; if all these conditions are met, they will do well in captivity without much intervention on your part!

Geophagus steindachneri - Red Hump Eartheater

However, it is important to note that Astronotus ocellatus is not an ideal beginner fish: its large size and need for high oxygen requirements make them more suitable for advanced aquarists or commercial operations. It’s important when setting up tanks containing Oscars to leave plenty of room for them to swim and create territories within, as they require a lot of space compared to other cichlids, especially during the breeding season.

This usually means at least 60 gallons per adult Oscar, though some sources recommend at least 100 gallons per couple or trio; in any case, larger is better! They’re also messy eaters who tend to stir up substrate when searching for food at night.

Oscar tank mates

Astronotus ocellatus are aggressive toward other fish, except for smaller ones. In a large tank, you can keep multiple fish of various sizes together without major problems. If you want to keep more than one in a tank, make sure you have a very large aquarium with plenty of hiding places. Even if they get along in a smallish aquarium when they’re young, adult Oscar cichlids will fight viciously to defend their territory.

Some good tank mates are other large Central American cichlids like Jack Dempsey, or large catfish. Note that some of these fish can grow to be extremely large and aggressive. For example, a 6-inch Jack Dempsey can weigh as much as five Astronotus ocellatus. Be careful if you decide to keep other fish with your Oscar; they may fight or become stressed in such a small environment!

Oscar fish breeding

Astronotus ocellatus - Oscar Cichlids

Because Astronotus are relatively easy to breed, they are often used as a first cichlid for novice aquarists. They will happily lay their eggs on aquarium glass if given flat stones or other such surfaces to use as an egg depository. If you don’t want to raise baby cichlids, take away any eggs that are laid to reduce the chances of having your fish end up with mouth-rot.

The adults can be removed after spawning is complete; however, it is best to leave them in place so they continue feeding at least part-time on unfertilized eggs. When breeding Oscars, water hardness should not be kept below 10 dGH and ideally will be maintained above 12 dGH for optimal health and coloration of adults and fry.

Water temperature should also be maintained between 75–78°F (24–26°C); these temperatures help ensure good fertility in females. Parents may eat newly hatched fry, but they usually do better if moved to a separate tank soon after hatching. Fry should grow quickly and spawn themselves around 6 months of age under good conditions; wild-caught specimens may require up to two years before they’re ready to mate.

Herichthys carpintis (Pearlscale Cichlid)

Are they aggressive or peaceful?

The Oscar cichlid is a large, aggressive fish that needs plenty of space to do its thing, they can also be territorial with other Oscars or similarly sized fish. It’s best to house one Oscar per tank or keep them in a tank that is over 60 gallons so there is plenty of room for each fish to establish a territory.

Oscar fish care

Oscar Cichlids

Astronotus ocellatus is a large fish that requires plenty of space for swimming, especially when housed with other Oscars. Due to their aggressive nature, two Oscars should not be kept in one tank unless they are bonded to each other. This can be difficult because, unlike many cichlids, Oscar species aren’t naturally social with others of their own kind. For maximum success, introduce only a single male per aquarium; if multiple males are added to an aquarium containing females, they will likely fight until one establishes dominance. Before attempting to house more than one male per aquarium, it’s important to research breeding protocols and ensure you have enough room to grow juveniles before adding adult fish into your aquarium setup.

Oscar food

Astronotus ocellatus are omnivorous. A 50/50 ratio of meaty foods to vegetable matter is ideal, but they’ll eat pretty much anything – including flakes, pellets, spirulina, brine shrimp, and live foods like bloodworms. They also need a generous amount of fiber in their diet to prevent digestive problems.

To feed them properly you will need high-quality flake food as well as some frozen or freeze-dried vegetables such as spinach or zucchini. You should also supplement with mineralized crushed coral or a multi-vitamin every couple of days for bone growth and enhanced coloration.

Water parameters

Oscar Cichlids

These fish are native to Central America and require hard alkaline water. The pH should be between 7.0-8.0 and the temperature should be kept at around 22°C (72°F). Astronotus ocellatus do best in moderately planted aquariums with large rocks to create caves for them to hide in. They prefer tanks that have a lot of open swimming space as well as areas where they can dig.

Provide plenty of vegetation, hiding spots, and driftwood branches. It’s also important to keep up on maintenance – make sure your filtration system is running smoothly, provide regular partial water changes and keep an eye out for algae growth. If you notice any white spots appearing on your plants or gravel, then you likely have an ammonia spike which will harm your cichlids very quickly.

Blacknose Shiner (Notropis Heterolepis)

Oscar fish lifespan

Astronotus ocellatus can live for up to 10-15 years in captivity. Wild Oscar fish have much shorter lifespans, around 8 years. The oldest Astronotus was 19-years-old when it died.

Oscar fish diseases

Astronotus ocellatus, commonly known as Oscar cichlid or chocolate cichlid, is a freshwater fish found in Central America. Named after fictional character Oscar from The Adventures of Tintin comic series. Oscar cichlids are peaceful and active freshwater fish that get along well with other aquarium fish such as zebra danio, tiger barbs, rasboras, tetras and swordtails, etc.

They can also be kept with more aggressive species like African rift lake cichlids provided they are introduced into an established tank. They will eat any meaty food including flake food.


Astronotus ocellatus are sought out by larger cichlids such as tiger barbs, flowerhorn cichlids, plecostomus, and convicts. Also, note that some of these species have been known to exhibit aggressive behavior towards other fish in general, so if you choose to house them with other fish, make sure it’s a large enough tank for these carnivores! Some tetras will also eat Astronotus ocellatus fry and juveniles.

It is also a good idea to keep them away from large tropical fish like goldfish, as well as other cichlids.

Do they make good pets?

Even though these cichlids are great for experienced fishkeepers, they may not be suitable as a first pet. Oscars can grow up to 14 inches in length, and their voracious appetites, aggressive behaviors, and potential lifespan of 15 years make them less than ideal pets for novice aquarists. You may want to consider other types of freshwater aquarium fish if you’re new to keeping fish or interested in trying your hand at being a hobbyist.