Lemon Oscar Care Sheet

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If you have a large tank and you’re looking for an interesting, characterful fish that’s strikingly attractive and super-intelligent, you might want to consider the South American Lemon Oscar cichlid (Astronotus ocellatus). Oscars are also very friendly fish that can bond with their keepers, watching as you move around the room, reacting to your voice, and begging for food.

Read this guide to find out more about the absolutely gorgeous lemon oscar and learn how to care for these remarkable fish.


Oscars are natives of South America, specifically the Amazon River Basin, the Rio Paraguay, the Parana, and the Rio Negro.

The species was first described in 1831 by Louis Agassiz and was given the scientific name Astronotus ocellatus. Oscars are also commonly known as the velvet cichlid, tiger oscar, and marble cichlid.

Many varieties of oscar fish are kept in the aquarium hobby, most of which have been artificially produced through cross-breeding to create more interesting and vivid color morphs. The lemon oscar falls into that category.

Natural habitat

In nature, oscars inhabit the slow-moving waters of ponds, canals, and rivers where the substrate is sandy or muddy. The fish are carnivorous, feeding on insect larvae, worms, crawfish, and small fish.

As juveniles, oscars live in small groups. However, as the fish reach adulthood, they become more solitary. So, if you keep lemon oscars in your tank, you should keep one individual specimen or a pair if you want to try breeding them.


Astronotus ocellatus

Lemon oscars are large fish, growing to reach up to 12 inches when adults if kept in a large tank and provided with optimum water conditions and a nutritious, varied diet. In captivity, oscars generally live for up to ten years.

All oscars have an oval-shaped body, large and thick lips, and tend to be somewhat dark in color. However, the lemon oscar is a vibrant yellow, hence its common name. When stressed or excited, the fish’s colors become more intense and brighter.

Lemon Oscar care guide

Tank size

Juvenile lemon oscars can live in a modest tank of around 30 gallons. However, these fish grow pretty quickly, and once fully mature, they need an aquarium of at least 100 gallons or larger.

These fish can be aggressive, so you will need a considerably larger tank if you want to keep a breeding pair or with other species of large cichlids.

Oscars are large fish that need plenty of swimming space and a well-oxygenated tank, so we recommend a long tank with plenty of surface area for optimal gaseous exchange rather than a tall tank. The tank must also have a tightly fitting lid to prevent the fish from jumping out and splashing water everywhere when feeding.


Lemon oscars need a stable environment where the water parameters remain consistent. As well as an efficient filtration system, you’ll need to carry out 20 to 40 percent partial water changes every week, clean and replace the filter media when required, and vacuum the gravel each week.

Oscars are very messy eaters, spitting out bits of live fish and worms. So, if you decide to give your fish live food, you will need to be diligent and thorough in your tank cleaning duties, possibly even cleaning the tank more frequently.

Although these fish do not like a strong flow, you do need to provide efficient filtration. They also need highly oxygenated water, so we recommend that you provide at least one air stone.

Water parameters

Lemon oscars are tropical fish, needing a water temperature of 72 to 77 degrees Fahrenheit. The pH range should be between 6.5 and 7.2. These fish do not tolerate brackish water.

Tank decoration

Lemon oscars swim in all areas of the tank, so be sure to leave space for them to move around. These are big, active fish, so you need to keep all equipment like outlets, inlets, and heaters either protected by immovable objects or well-hidden. Ideally, you should choose an external filtration system and heater.

Oscars appreciate a sandy substrate, as they are card-carrying diggers. They also like plenty of hiding places, mostly in the form of driftwood and rocks. Rockwork must be well buried in the substrate, ideally on the glass bottom to prevent the rocks from becoming dislodged or toppled over.

Although live plants make a great addition to any tank, helping to oxygenate the water and absorbing nitrates, lemon oscars will readily eat, shred, or dig up your planting. With that said, floating varieties of plants make a good alternative, and the oscars will appreciate the plants’ cover.

Diet and nutrition

Lemon oscars are carnivores that need a diet made up entirely of meaty protein.

Although these fish prefer to eat live food, they will eat frozen, dead, or pelleted food as an alternative. Good foods for oscars include chopped up earthworms, prawns, and fish. If you feed these fish live foods, opt for worms, feeder goldfish, and guppies.

Foods like beef hearts, chicken, pork, and more were once considered to be safe for oscars to eat. However, it’s now thought that the high fat and protein content that these foods contain, which don’t occur naturally in the fish’s diet, can cause severe digestive problems for the fish and should therefore be avoided.

How often and how much to feed?

Ideally, you should feed your fish twice or three times each day, offering only what they will clear in a few minutes per feed. However, if you’re offering your oscars live food, you may need to allow extra time for the fish to catch their prey.

Tank mates

Unfortunately, lemon oscars don’t make good community fish. Although they are quite good-natured with large fish, oscars are confirmed predators that will eat most smaller fish. But if you have a large tank of over 200 gallons, you can probably keep a few other large, semi-aggressive fish, such as plecostomus, arowanas, and Jack Dempseys.

You can keep two oscars together for breeding purposes, but mature fish will become territorial with other members of its species. So, if you don’t plan on breeding your oscars, it’s generally safer to keep just one specimen.

Unfortunately, you can’t keep invertebrates like snails, crabs, shrimp, crayfish with oscars, as these critters will undoubtedly be viewed as a food source.


Lemon oscar fish in aquarium

Lemon oscars are pretty easy to breed in captivity. In fact, the most difficult aspect of breeding 0scars is sexing them, as there’s really no visual difference between the female and male adult lemon oscar cichlid.

If you want to breed these fish, the best strategy is to buy six to eight young fish and allow them to pair off naturally as they become sexually mature when they reach about 4.5 inches in length.


Lemon oscars are egg-layers and open spawners. Set up a spawning tank with plenty of space; a 100-gallon tank is ideal for a breeding pair. The water should be clean and clear and at a temperature of between 78.8 to 86 degrees Fahrenheit.

Line the bottom of the tank with flat, smooth stones as a spawning substrate on top of soft sand. The female will drop between 1,000 and 2,000 eggs on stones that she has carefully cleaned first. Both parents guard the eggs, and when the fry hatch, they’re kept in a pit and sometimes buried.

Once the fry is free-swimming, they can be fed Cyclops.

Health and disease

Lemon oscars are pretty resilient when it comes to diseases, but the best way to keep your fish healthy is to keep their tank scrupulously clean as described above and feed them a correct, nutritious diet.

Diseases that can affect oscar fish include:

Head and Lateral Line Erosion (H.L.L.E.)

H.L.L.E. is also known as Hole-in-the-head disease and is very common in the 0scar cichlid.

The disease presents itself as pits or cavities on the fish’s face and head, and it’s thought to be caused by a poor diet that lacks vitamins C, D, phosphorus, and/or calcium. Poor water quality and over-filtration with chemical filter media like activated carbon are also thought to be possible causes.


Ich is also known as white spot disease and is caused by an aquatic parasite called Ichthyophthirius multifiliis.

As the parasite’s lifecycle progresses, the fish can be observed flicking against solid objects within the tank, including the substrate. After a few days, a scattering of tiny white spots appears on the fish’s body, gills, and fins.

Although ich is treatable if you catch it early, the condition can be fatal if it’s left to progress. Stop ich in its tracks by increasing the water temperature to 82 degrees Fahrenheit for three days, and treat the water with a condition-specific medication.


Flukes are another type of parasite that sometimes attacks oscars. Flukes attach themselves to the fish’s gills or body and are often visible to the naked eye.

The parasites usually get into your tank on plants, attached to fish, or with live food. Much like a case of ich, you can dispose of flukes by treating the water with an anti-parasitic medication.

Bacterial infections

Almost every fish tank contains various species of bacteria, and most of the time, these bacteria don’t cause problems. However, if fish are weakened by injury or stress, bacteria can cause problems.

Bacterial infections show up as reddened patches on the fish’s skin, sores, and ulcers, and they can also cause general discomfort and loss of appetite.

Most bacterial infections are treatable, however, so long as you use an antibacterial medication and carry out more frequent water changes.


Types of fungi appear as white, cotton-like growths on the fish’s head, body, and fins. The condition is usually associated with fish that are kept in dirty tanks with poor water conditions, and it can be treated with an antifungal medication.

Where can I buy fish medication?

You can purchase medication to treat the fish’s most common diseases from your local pet or fish store or online. You don’t need a prescription from your veterinary surgeon for these drugs, however, if you can’t find the treatment you need over-the-counter, ask your vet for advice.

How can I prevent fish diseases in my tank?

The good news for hobbyists is that most fish diseases can be prevented relatively easily. Just follow a few simple steps.

  • Keep your new lemon oscar in quarantine for at least ten days before introducing them to your main tank.
  • Wash plants and decorations in a solution of antibacterial medication and water to kill off any parasites and bacteria and keep them out of your tank.
  • Buy live food from a reputable supplier. Remove the food from the water in which it came before giving it to your fish.
  • Never take live food from nature.
  • Keep your lemon oscar tank scrupulously clean by carrying out regular water changes.

Monitor your fish daily

Make it a habit to check your fish daily for signs of potential problems that may be brewing.

Oscars are very active fish that have a healthy appetite, so if you spot any lethargic fish or aren’t interested in food, remove them from the tank and place them in quarantine to prevent any disease from spreading. Early treatment is the key to preventing your pet fish’s death, so always be vigilant.


The lemon oscar (Astronotus ocellatus) is widely bred commercially, so they are usually readily available. Typically, you can expect to pay a pretty low price for a nice specimen.

Generally, small juvenile fish are less expensive than larger ones. Also, the brighter the yellow coloration of the fish, the more expensive it will be.

Final thoughts

The lemon oscar, also known as Astronotus ocellatus, is a beautiful variation of the ever-popular oscar cichlid.

These fish make a spectacular, vibrant addition to a very large aquarium, but they’re best kept alone or as a breeding pair, as they are territorial and predatory, and they will eat smaller fish and invertebrates. That said, lemon 0scars do have their own personalities, being friendly, inquisitive fish that can form a bond with their owners.

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