Can I Keep An Oscar In A 55-Gallon Tank?

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Oscars are one of the most interesting fish kept in home aquariums. They are extremely beautiful too. However, when it comes to the tank’s size, they are pretty demanding.

Can you actually keep them in a tank of 55 gallons? Are you about to face some troubles? How do you do this right? And what other fish species can you bring along?

In this article, you’ll learn everything there is to know about this topic. So, without further ado, let’s get started.

Can an Oscar Fish be Kept in a 55-Gallon Tank?

Yes, an Oscar fish can be kept in a 55-gallon tank. However, it’s the minimum recommended size for a single adult Oscar. Here are some reasons why:

  • Space Requirements: Oscar fish can grow up to 12-14 inches long. A 55-gallon tank provides enough room for one adult Oscar to move and turn comfortably.
  • Behavioral Health: Oscars are active swimmers. A 55-gallon tank gives the Oscar fish sufficient space to exhibit natural behaviors without stress.
  • Water Quality: Larger volumes of water are more stable. A 55-gallon tank helps in maintaining consistent water parameters essential for the Oscar fish’s health.
  • Decor and Territory: Oscar fish are territorial. A 55-gallon tank allows for decor placement, enabling the Oscar to establish its territory.
  • Growth Consideration: Starting with a juvenile Oscar in a 55-gallon tank ensures it can grow without the need for immediate upgrades.

Also Read: Oscar Fish Tank Size

How Do You Calculate the Recommended Tank Size for Oscars?

Here is how to calculate the appropriate tank size for an Oscar fish:

  • Oscars grow to an adult size of 12-14 inches.
  • General fish tank rule is often 1 gallon of water per inch of fish.
  • Oscars are larger, more active, and produce more waste than average fish.
  • Instead of the general rule, Oscars might need 3-5 gallons per inch.
  • For a single Oscar: 12 inches x 3-5 gallons/inch = 36-60 gallons.
  • Incorporate space for decor, substrate, and filtration equipment.
  • Given the factors and for comfortable space for a single Oscar, 55-75 gallons is recommended.

Also Read: Can You Keep An Oscar Fish In A 75-Gallon Tank?

Maintenance Tips For A 55-Gallon Tank With Oscar Fish

Maintaining a 55-gallon tank with Oscar fish is a task that demands thoroughness and dedication.

Ensuring that the tank environment is consistently stable and clean is imperative for the health and happiness of your Oscar fish. Here’s a detailed breakdown:

  • pH Levels: Oscar fish prefer a pH level between 6.0 to 8.0. Using a pH tester weekly helps monitor this. My recommendation: API FRESHWATER MASTER TEST (link to Amazon).
  • Temperature: Maintain a water temperature between 74°F (23°C) and 81°F (27°C). Invest in a reliable aquarium heater and thermometer. My recommendation: Fluval E300 Advanced Electronic Heater (link to Amazon).
  • Filtration Capacity: A filter with a capacity to handle at least 200 gallons per hour (GPH) is ideal for a 55-gallon tank with Oscar fish. This is nearly 4 times the tank’s capacity, ensuring waste is effectively processed.
  • Sturdy Objects: Oscars are known to be a bit boisterous. Choose heavy rocks or driftwood that weigh at least 2-3 pounds to prevent easy displacement.
  • Plants: Live plants can be uprooted by Oscars. If opting for them, select robust plants like Java fern or use artificial plants.
  • Water Changes: Every week, replace 20-30% of the tank water. Using a dechlorinator is crucial when adding tap water. I personally use the Tetra AquaSafe (link to Amazon).

Is It Possible To Add More Oscar Fish To A 55-Gallon Tank?

For optimal health and behavior, a 55-gallon tank should house no more than one adult Oscar fish.

Adding more Oscar fish to this sized tank would likely lead to overcrowding and stress. 

Here’s why:

  • Growth Rate: Oscar fish are known for their rapid growth, often reaching sizes of 12-14 inches in adulthood, which means they require ample space.
  • Territorial Nature: Oscars have a strong territorial nature. In confined spaces like a 55-gallon tank, this can escalate to increased aggression and disputes among them.
  • Water Quality: A higher number of Oscar fish in the tank translates to increased waste. This can lead to faster degradation of water quality, demanding more frequent maintenance in a 55-gallon tank.

Also Read: Can An Oscar Live In A 40-Gallon Tank?

Can Several Baby Oscars Be Raised in a 55-Gallon Tank?

While baby Oscar fish can initially be housed in a 55-gallon tank, they’ll quickly outgrow it and need larger accommodations.

Raising multiple baby Oscars in such a tank is only a short-term solution. To understand this better:

  • Initial Size: At their youngest, baby Oscar fish are roughly 1-2 inches, making the spaciousness of a 55-gallon tank deceptive at first.
  • Rapid Growth: Oscar fish are fast growers. Within their first year, they can reach sizes close to 10 inches, which makes a 55-gallon tank inadequate in the long run.
  • Stress Risks: Crowded conditions as the Oscars grow can result in stress, potentially leading to various health problems or aggressive behaviors.
  • Upgrade Need: Considering their growth rate and space needs, Oscars require between 3-5 gallons of water for every inch they grow, emphasizing the need for a larger tank as they mature.

How Many Gallons Does Each Additional Oscar Fish Require?

Each additional Oscar fish, considering their potential adult size, would ideally require between 55-75 gallons of additional space.

This is essential to ensure their health and activity needs are met.

Here are the specifics:

  • Size and Space: Considering that a mature Oscar fish can be anywhere from 12-14 inches in length, they demand between 3-5 gallons of water for each of those inches.
  • Water Quality: Every Oscar fish added contributes more waste, making it essential to have more water to dilute the pollutants and maintain good water quality.
  • Activity Level: Being dynamic swimmers, Oscar fish thrive when they have sufficient space for swimming, playing, and exploring without restrictions.

Does The Gender Of Oscar Fish Matter In A 55-Gallon Tank Setup?

Yes, the gender of Oscar fish does play a role in a 55-gallon tank setup. The interaction dynamics can be different based on the gender combinations of Oscar fish in the tank.

Here’s how gender plays a part:

  • Aggressive Males: Male Oscar fish tend to be more aggressive, especially when establishing territories or vying for mates.
  • Breeding Behavior: If you have both a male and female Oscar fish, there’s potential for breeding, which brings its own set of challenges.
  • Same-gender Compatibility: Two females might coexist more peacefully than two males, but individual temperament varies.
  • Space Requirements: Regardless of gender, each Oscar fish will still require ample space, but males might demand larger territories.

Can Oscar Fish Be Successfully Bred In A 55-Gallon Tank?

No, while Oscar fish can potentially breed in a 55-gallon tank, it’s not the ideal environment for successful breeding and raising of the fry.

Here’s why this setup is suboptimal:

  • Space Constraints: Oscar fish require space for breeding rituals, and a 55-gallon tank might be limiting.
  • Egg Laying: Female Oscar fish lay hundreds of eggs, and the tank might not provide enough space for them.
  • Protection of Fry: A larger tank aids in the survival rate of the fry as it gives them more space to hide and thrive.
  • Parental Aggression: Post breeding, Oscars can become aggressive, especially towards perceived threats to their fry.
  • Water Quality: Increased waste from the fry and uneaten food can degrade water quality faster in a 55-gallon tank.

How Many Oscar Fish Should Be Kept Together In General?

Ideally, Oscar fish should be kept individually or in pairs if provided with ample space. Keeping multiple Oscars requires careful consideration of space and their territorial nature.

Here is what you should know:

  • Territorial Behavior: Oscar fish are territorial, especially males, which can lead to conflicts in a limited space.
  • Tank Size: For every Oscar fish, a minimum of 55-75 gallons is recommended to ensure sufficient space.
  • Environmental Enrichment: Multiple Oscars mean the need for more hides and territories within the tank setup.
  • Compatibility: While some Oscars might coexist peacefully, others based on individual temperament might not, requiring constant observation.

Keeping Other Fish Species With Oscar Fish In A 55-Gallon Tank

There are a few species that are often brought up when considering tank mates for Oscar fish.

Here’s a brief explanation of each one, including whether they are compatible with Oscars in a 55-gallon tank:

1. Silver Dollar Fish

Silver Dollar Fish can be compatible with Oscar fish due to their similar size and temperament.

However, proper care and conditions are essential to ensure compatibility in a 55-gallon tank.

Here’s what makes them compatible:

  • Size Match: Silver Dollar Fish grow to around 6 inches, reducing the risk of being bullied by the larger Oscar fish.
  • Temperament: They are generally peaceful and can adapt to the Oscar fish’s active and sometimes aggressive behavior.
  • Diet: Both species have similar dietary preferences, which makes feeding them together more manageable.
  • Water Conditions: Silver Dollars can adapt to the same water conditions as Oscar fish, simplifying the maintenance.

2. Convict Cichlids

Convict Cichlids might coexist with Oscar fish, but they also can be territorial and aggressive.

To make this work:

  • Size Concerns: Convict Cichlids are smaller, around 3-5 inches, which might lead to conflicts with Oscar fish.
  • Aggression Match: Both species are territorial, so providing enough hiding spots and territories is essential.
  • Breeding Behavior: If Convict Cichlids breed, they become extremely aggressive, posing a potential problem.
  • Similar Water Needs: Convict Cichlids and Oscar fish share similar water condition requirements, easing the maintenance.

3. Firemouth Cichlids

Firemouth Cichlids can be housed with Oscar fish, but caution must be exercised due to their smaller size and territorial nature.

Factors to consider:

  • Size Difference: Firemouth Cichlids are smaller (around 6-7 inches) and may become targets for Oscar fish.
  • Temperament Compatibility: Although territorial, their generally milder temperament might be compatible with Oscars.
  • Dietary Needs: Sharing similar dietary habits, both species can be fed similar food.
  • Water Parameters: Firemouths and Oscars thrive in similar water conditions, which helps in tank maintenance.

4. Bristlenose Plecos

Bristlenose Plecos can be kept with Oscar fish, mainly serving as algae eaters in the tank.

Here’s why they can be suitable:

  • Size and Nature: Growing to 4-5 inches, they have a different ecological niche and generally avoid confrontation with Oscar fish.
  • Algae Eating: Bristlenose Plecos help control algae, contributing to the tank’s cleanliness.
  • Hiding Spaces: They require hiding spots, so providing adequate caves and shelter is crucial.
  • Water Conditions Compatibility: Both species thrive in similar water parameters.

5. Severum Cichlids

Severum Cichlids might cohabit with Oscar fish, considering their similar size and temperament.

Here are key points:

  • Size Compatibility: Severums can grow up to 8 inches, making them less prone to intimidation by Oscar fish.
  • Temperament Match: They share a relatively peaceful temperament, making compatibility possible.
  • Dietary Similarities: Both Severums and Oscar fish enjoy varied diets, including meaty foods and pellets.
  • Water Requirements: Both species need similar water conditions, which can make care and maintenance simpler.

6. Geophagus Cichlids

Geophagus Cichlids can be an interesting companion for Oscar fish, but compatibility depends on the specific species.

Key considerations include:

  • Species Specifics: The compatibility varies among species within the Geophagus genus, requiring careful selection.
  • Size Range: Geophagus range in size from 6-12 inches, which can work well with Oscar fish.
  • Diet Compatibility: Both fish types have omnivorous diets and can eat similar foods.
  • Water Parameters: They thrive in similar water conditions, aiding in the maintenance of a shared tank.

7. Silver Sharks

Silver Sharks may not be the best companions for Oscar fish, especially in a 55-gallon tank.

Here’s why:

  • Size Mismatch: Silver Sharks can grow up to 14 inches, potentially outgrowing a 55-gallon tank with Oscar fish.
  • Activity Levels: They are very active swimmers and may require more space than a 55-gallon tank provides.
  • Potential Stress: Their active swimming might stress the Oscar fish in a confined space.
  • Water Conditions: Although they share similar water requirements, the size and activity mismatch can create compatibility issues.


For those of you who are just skimming through, here is a quick recap:

  • A 55-gallon tank provides sufficient space for an adult Oscar fish, accommodating growth, natural behavior, and territory establishment.
  • Maintenance of a 55-gallon tank with Oscars demands consistent attention to pH levels, temperature, filtration, decor, and water changes for their well-being.
  • Adhering to the one-adult Oscar guideline in a 55-gallon tank prevents stress and aggression, considering their rapid growth and territorial tendencies.
  • While suitable for young Oscars, a 55-gallon tank requires future upgrades as they grow rapidly, ensuring their long-term comfort and health.
  • Gender dynamics impact social interactions in a 55-gallon tank; understanding male aggression, breeding, and space needs fosters a harmonious environment.