Best Oscar Tank Mates

What makes a good tank mate for an oscar?

A good oscar tank mate is too big to swallow, even after the oscar finishes growing, calm enough not to bully it, and comfortable in the same warm water. The oscar (Astronotus ocellatus) is a large cichlid from the Amazon and Orinoco basins that reaches 14 in (35.6 cm) by Seriously Fish’s measure. Four criteria follow from the sources in our oscar data.

1. Too large to eat. Seriously Fish and Aquarium Co-Op both say the oscar will eat any fish small enough to swallow, and they advise against much smaller fish and nano species. This single rule removes most aquarium fish.
2. Not a bully. Aquarium Co-Op notes that the oscar can itself be bullied by other large, aggressive fish. A tank mate big enough to be safe must not be so aggressive that the oscar becomes the victim.
3. Shared warm water. Oscars need 74–80 °F (23–27 °C), pH 6.0–8.0 and 5–20 dGH. The pH and hardness ranges are wide, so temperature and size decide most pairings.
4. Tolerant of a bare, rearranged tank. Seriously Fish and Aquarium Co-Op both say oscars dig, uproot plants and rearrange decor, so tank mates that depend on dense planting lose their cover.

Temperament is the criterion people expect to matter most, yet it matters least here. Seriously Fish calls the oscar not especially aggressive for a cichlid of its size; the risk it poses is predation, not fighting. The other pages in our tank mates by species series apply the same criteria to smaller fish.

Which species in our data can live with an oscar?

The angelfish is the only fish in our data that scores well with an oscar, and even that result rests on numbers rather than on any source that recommends the pairing. Two snails also score well, with caveats from their own care sheets.

Angelfish

The angelfish scores 7/10. The two share 75–80 °F (24–27 °C) and pH 6.0–8.0, and an adult angelfish reaches 6 in (15.2 cm), which keeps the size gap just inside the limit our method treats as a predation risk. That is the whole case for the pairing. No source in our oscar or angelfish data assesses the two together, and three facts argue for caution. Juvenile angelfish are smaller than adults, and Aquarium Co-Op says oscars grow to about two-thirds of adult size in their first 6–12 months. Angelfish have long fins and, according to Seriously Fish, squabble when they form territories. Both species are semi-aggressive, which is why the shared tank is 125 US gal (473 L). The angelfish tank mates ranking shows how angelfish fare with other companions.

Nerite and mystery snails

Nerite snails score 8/10 and mystery snails 7/10, because no source in our oscar data says whether oscars eat snails. The snails’ own care sheets point the other way. Aquarium Co-Op and Maidenhead Aquatics list large or aggressive cichlids among the nerite’s threats, and Aquarium Co-Op and Applesnail.net name larger strong-jawed fish such as cichlids as a threat to mystery snails. Treat both scores as unproven. The guide to aquarium snail tank mates lists safer settings for snails.

Why do so few fish in our data suit an oscar?

Few fish suit an oscar because our species data covers mainly small community fish and invertebrates, and almost all of them are small enough for an adult oscar to eat. The largest fish in the data besides the oscar are goldfish, angelfish and discus, and none of them is a proven oscar companion: goldfish fail on temperature, discus on temperature and size, and the angelfish passes only on the numbers.

The sources behind our oscar data describe which fish to avoid more clearly than which fish to choose. Seriously Fish and Aquarium Co-Op say to avoid much smaller fish and nano species; Aquarium Co-Op adds that other large, aggressive fish may bully an oscar. None of these sources names a list of recommended oscar tank mates that we could verify, so we do not name species we have no data for. A suitable companion would need to match the criteria above: an adult size well beyond what an oscar can swallow, a temperature range overlapping 74–80 °F (23–27 °C), and a temperament calm enough not to harass the oscar.

Other large-cichlid communities have their own pages, such as the guide to compatible tank mates for African cichlids. To test any species we do cover against the oscar, use the species compatibility checker.

Which fish should never live with an oscar?

Every small community fish in our data fails with an oscar, almost always because the oscar can eat it. Seriously Fish and Aquarium Co-Op describe the oscar as a generalised predator of smaller fish and crustaceans, and our method fails any pairing where a fish-eating species is several times longer than its companion.

Tetras, rasboras and danios

Neon tetras, cardinal tetras, GloFish tetras, harlequin rasboras and zebra danios all fail on size; the neon tetra, for example, scores 3/10. They are nano or small schooling fish, the group Seriously Fish and Aquarium Co-Op single out as unsafe. Zebra danios also share only 74–75 °F (23–24 °C) with the oscar.

Bottom dwellers, including the bristlenose pleco

Corydoras, kuhli loaches and bristlenose plecos score 3/10, 3/10 and 3/10. The bristlenose is the largest, at 5 in (12.7 cm), but the size gap still crosses the method’s predation threshold. Our data covers only the bristlenose, so this result says nothing about larger pleco species.

Livebearers, bettas and gouramis

Guppies, platies, mollies, Endler’s livebearers, bettas and dwarf gouramis all fail on size; the molly is the largest of them at 5 in (12.7 cm). The fish that live with bettas page explains that oscars are among the betta’s worst possible companions.

Goldfish and discus

Goldfish score 3/10 for a different reason: they are coldwater fish kept at 59–70 °F (15–21 °C) and share no temperature range with the oscar. Discus score 3/10: the shared temperature is only 79–80 °F (26–27 °C), and at 5.5 in (14 cm) a discus is still within the size gap our method treats as a predation risk.

How big a tank do an oscar and its tank mates need?

An oscar with any tank mate needs 125 US gal (473 L) in our data, and one oscar alone needs at least 75 US gal (284 L). Aquarium Co-Op recommends 75 gallons for one oscar and 90 to 100 gallons for two. Seriously Fish gives a 150 × 60 cm base as just enough for one adult but does not give a height, so no volume can be derived from it.

The shared figure is larger than either fish’s own minimum because the method takes the bigger of the two minimums, adds a margin when a semi-aggressive species is involved, and rounds up to the next common tank size. Every oscar pairing in our data reaches the same figure, whatever the companion. Plan the full stock with the stocking calculator.

Small tanks belong to a different kind of fishkeeping. The fish in the guide to choosing fish for a 10-gallon community tank are the nano and small species that Seriously Fish and Aquarium Co-Op say an oscar will eat, so none of them should be added to an oscar tank of any size.

An oscar that outgrows its tank needs rehoming, not release. The USGS Nonindigenous Aquatic Species profile (revised 2013) lists the oscar as established in south Florida, Hawaii and Puerto Rico and records introductions that failed in 21 states, noting that oscars grow large in aquaria and are likely to be released.

Can oscars live with other oscars?

Oscars are best kept singly or as a pair. Seriously Fish suggests a single fish or a pair, and our oscar data notes that groups work only if raised together from juveniles in a large tank. Aquarium Co-Op warns that several oscars often develop territorial fights that force the removal of some fish. Aquarium Co-Op notes that oscar aggression rises mainly in spawning seasons, and the breeding sources in our oscar data describe both parents guarding eggs laid on a flat rock or cleared pit. A pair needs the larger tank Aquarium Co-Op describes, rather than the single-oscar minimum.

Can a young oscar grow up safely with small fish?

No. A common belief is that small fish raised with a juvenile oscar will be accepted as tank mates, but no source in our data supports it. Aquarium Co-Op says oscars grow fast, reaching about two-thirds of adult size in their first 6–12 months, and both Seriously Fish and Aquarium Co-Op describe a predator that eats any fish that fits in its mouth. A fish that is safe beside a young oscar becomes food as the oscar grows.

The opposite misconception is that oscars are simply aggressive. Seriously Fish calls the oscar not especially aggressive for a cichlid of its size, and Aquarium Co-Op notes it can be bullied by larger aggressive fish. The problem with small tank mates is appetite, not temper, which is why a peaceful score elsewhere on this site does not carry over to an oscar tank.

Can oscars live with shrimp?

No. Our oscar data records that oscars eat dwarf shrimp, and Aquarium Co-Op says they eat any invertebrate small enough to fit in their mouths. Cherry shrimp score 3/10 and amano shrimp 3/10, because a fish recorded as eating both small fish and shrimp, and many times their size, is a deal-breaker in our method; the cherry shrimp tank mates guide covers the safer options. Aquarium Co-Op also lists medium to large cichlids among the fish that eat amano shrimp, and the oscar’s habit of uprooting plants removes the cover shrimp need.