Should I buy it?
Oscar
Astronotus ocellatus
Also known as: velvet cichlid
Massive personality, even more massive tank requirement. A single oscar realistically needs 300L+ and produces enough waste to push your filter to its limit.
Oscar tank mates · 300L tank size hub
aggressive · intermediate care
Sources & confidencehigh · verified · beginner: not recommended
Checked against several solid care sources that mostly agree. Numbers here are a careful starting point. Your tap water, tank size, and habits decide the rest. How we evaluate.
Best for: Single-species or oscar-pair setups with 300L+ and serious filtration. People who genuinely want a 'wet pet'.
Avoid if: You have anything under 250L; want plants, small fish, or a low-maintenance setup.
Common mistakeKeeping two oscars in 200L is how keepers invent nitrate spikes and fish with nowhere to turn. Adults need real footprint and a water-change discipline that matches appetite. A 'pair in a big 200L' is still too small for the turning radius and bioload.
Top things that go wrong
- Grows large or needs a very big footprint. Oscar is often sold at sizes that hide adult length (~35cm) and a published minimum near **300L**. Shop tanks are not adult housing.
- Mouth gap vs tiny tank mates. May eat tank mates small enough to fit the adult mouth — plan adult sizes, not shop sizes.
- Shrimp & snails. Not shrimp-safe — adults, fry, or both get eaten.
What most shops don't tell you
- 1.Myth: oscars stay manageable in a 200L community if you only keep one or two and clean often. Reality: adults need roughly 300L+ each in practical terms for turning space and waste — under-housing makes water quality and aggression problems inevitable.
- 2.Predation risk scales with gape, night feeding, and crowding. 'they grew up together' is a schedule, not a law.
- 3.Two oscars in 200L. Adult turning radius and nitrates outpace a weekly water change habit.
- 4.Housing with small tetras. 'They grew up together' ends when one fits in a mouth.
- 5.Oscars produce the bioload of a small dog and need a 300L+ tank with serious filtration. They eat anything under 15 cm. Single-species or large-cichlid setups only.
About this species
Oscars are large South American cichlids that learn faces, beg for food at the glass, and will eat any fish that fits in their mouth. The adult is 30 to 35 cm.
- Green Terror300L min · same group, comparable tank size
- Severum250L min · same group, comparable tank size
- African Cichlid200L min · same fish family
- Convict cichlid200L min · same fish family
- Firemouth Cichlid200L min · same fish family
- Jack Dempsey200L min · same fish family
- Keyhole cichlid200L min · same fish family
- Rainbow cichlid200L min · same fish family
- African Cichlidalso intermediate aggressive, similar tank size
- Green Terroralso intermediate aggressive, similar tank size
- Jack Dempseyalso intermediate aggressive, similar tank size
- Common Pleco tank matesnames this fish as a conditional pairing — read the pair page conditions
- Green Terror tank mateslists this fish as a safe and recommended mate
- Jack Dempsey tank mateslists this fish as a safe and recommended mate
- Jaguar cichlid tank mateslists this fish as a safe and recommended mate
Plan grid
Key limits are above. Here: pH band, swim level, bioload, and activity.
Swim zones
Care snapshot
Quick compare before you buy. Not a score of how “good” the fish is.
- Beginner ease29
- Peacefulness0
- Community fit0
- Small-tank fit66
- Hardiness57
- Energy54
Numbers are deterministic planning indices from Fishori fields — not a scientific score of your individual fish.
Example setups
Starting points only. Run the pair checker for every fish you add.
Avoid “one of everything” baskets — Oscar belongs in a plan built around territory, line-of-sight breaks, and matched water chemistry.
Compatibility
Tank mates for Oscar
Usually safer (engine GOOD): Green Terror, Jack Dempsey. Conditional (CAUTION — read the pair page before buying): Angelfish, Common Pleco. Avoid (RISKY): Corydoras Catfish, Discus, Guppy, Neon Tetra, Tiger Barb. Every name links to a live pair check — the lists are a shortlist, not a stocking plan.
Usually safer
Open a pair page with this fish as the starting point.
Needs planning
Read the blocking rule on each pair page before experimenting.
Usually avoid
Do-not-stock combinations on conservative hobby rules.
Compare with
Run a real pair check: Oscar + Green Terror
- Try Green Terror — open the pair check.
- Try Jack Dempsey — open the pair check.
Behaviour and temperament
Oscars are aggressive, intelligent cichlids that rearrange tanks and eat what fits. They can recognise keepers and still destroy unsuitable tank mates. Stress and damage rise hard in short, under-filtered setups stocked with anything mouth-sized Plan the husbandry before the shop impulse buy.
What sets them off
- Crowding and limited territory
- Similar-looking fish in the same tank
- Spawning, for any breeding pair
Fin nipping: Not a habitual fin-nipper; stressed or crowded individuals can still test fins.
Predation: May eat tank mates small enough to fit the adult mouth — plan adult sizes, not shop sizes.
Territory: Holds a patch (cave, corner, or surface). Break sight lines so neighbours can pass.
Planted tanks: caution — pick tougher plants
In the glass: typical and warning signs
- An oscar patrols, digs, and begs at the glass in a large filtered tank.
- Rearranging décor is normal ownership — secure heaters and lids.
- Gasping and aggression spikes after skipped water changes mean bioload math failed.
- Missing small fish overnight mean predation, not a mysterious disappearance.
- Mouth-size predation and territorial attacks are expected with wrong stocking.
- Two oscars in tight quarters often fight as hard as they bond in bigger systems.
- Upgrade volume before adding a second oscar 'for company.'
- Remove all swallowable fish long before adult size arrives.
Fish behaviour can vary between individuals and tank setups. Always observe new fish closely after introduction.
Water, food, and grouping
Hardness
variable
Diet
carnivore
Oscars are large carnivore cichlids that need meaty foods and filtration that keeps up with serious waste. Feed appropriate pellets and frozen foods by appetite in 300L-class volume, and stop pretending a neon community diet applies. Overfeeding in undersized tanks turns the water into the main enemy.
Shrimp & snails
Not shrimp-safe — adults, fry, or both get eaten.
Oscar is fine singly or as a researched pair — check behaviour before doubling up.
- Hold 23 to 28 °C steadily on a real thermometer, not the dial on the heater.
- Aim for pH 6 to 8 and a hardness you can re-test in two weeks. A one-time strip in the shop car park is not a water test.
- Footprint: short wide tanks and tall narrow tanks fish differently for the same volume. Match the tank shape to the swim pattern, not just the litre count.
- Tank volume meets or exceeds 300L published minimum for adults.
- Heater can hold 23–28°C without cooking cooler-water tank mates.
- No tank mates small enough to fit the adult mouth gap for this species.
Explore and stocking hubs
Tank-mates hub, matching guides, category peers, and litre stocking lists around this species’ minimum tank.
Plan with tools
Check mates as pairs first, then add this fish in the tank builder for the full stocking.
Filtration & heating
A 300L minimum tank needs a filter rated for at least 1200L/hr turnover and a heater to hold 23–28°C reliably.
Research: verified · Confidence: high · 4 linked source(s). We do not invent citations.
How Fishori evaluates compatibility (same logic as pair and tank tools).
- Seriously Fish. Astronotus ocellatus
Primary: aquarium size, water chemistry, behaviour, and compatibility (URL verified in upgrade script; recheck if site content changes).
- FishBase. Astronotus ocellatus
Secondary: taxonomy, distribution, and maximum length in nature; cross-check with aquarium import lines and measured tank parameters.
- Wikipedia. Astronotus ocellatus
Secondary: general species context; verify all husbandry numbers against a dedicated aquarium care sheet and your test kit, not a single table row.
- Wikipedia. Astronotus ocellatus (oscar)
Encyclopaedia overview; use specialist aquarium sources for your stock's real temperature/pH/footprint needs.
Evidence notes
- The Seriously Fish profile for the binomial in this record was successfully reached as the primary aquarium reference.
- FishBase contributes natural-range size and habitat context. Translate those numbers through your heater, your water report, and your tank footprint before stocking.
- Wikipedia is only cited if the article URL returned OK. Use it for orientation, not as the only care sheet for an import.
- All compatibility text reflects typical hobby experience and the Fishori model. Individual fish, shop stress, and the order tank mates are added in can still defy a single-paragraph label.
Featured compatibility checks
Curated pair pages for Oscar. Each opens a full verdict — not just a list label.
Common questions about Oscar
- How big do Oscar get?
- 30 to 35 cm in eighteen months. Shop oscars are sold at 5 cm. That fish doubles in size every few months for the first year.
- What size tank does Oscar need?
- 300L is the absolute minimum for one adult. 450L+ for a pair. Footprint matters more than height: they need length to turn.
- Are Oscar aggressive?
- Oscars are aggressive, intelligent cichlids that rearrange tanks and eat what fits. They can recognise keepers and still destroy unsuitable tank mates. Stress and damage rise hard in short, under-filtered setups stocked with anything mouth-sized Plan the husbandry before the shop impulse buy.
- What is the most common mistake with Oscar?
- Keeping two oscars in 200L is how keepers invent nitrate spikes and fish with nowhere to turn. Adults need real footprint and a water-change discipline that matches appetite. A 'pair in a big 200L' is still too small for the turning radius and bioload.
- What fish can live with Oscar?
- The Oscar profile lists Green Terror, Jack Dempsey among its safer pairings (engine-checked GOOD). Angelfish, Common Pleco are conditional (CAUTION): workable only with the specific conditions on each pair page. Avoid Corydoras Catfish, Discus, Guppy, Neon Tetra (RISKY). Run the pair checker for your exact water and tank size before stocking.