The oscar fish is sold at three inches. It does not stay there
Every figure on this record is large, and one of them explains all the others. Aquarium Co-Op states that oscars are usually sold at 2 to 3 inches long, reach 10 to 12 inches or more as adults, and achieve two thirds of their adult size within the first 6 to 12 months.
That is the whole problem with this species in one sentence. The fish in the shop tank is a juvenile with a year of growing to do, and the tank it is bought for is almost never the tank it will need. This record carries a minimum of 75 gallons, which is the largest figure on this site by a wide margin, and it carries a lifespan of 10 to 20 years, which is longer than most aquariums last.
Everything else about the oscar is easier than its size. Two sources publish the same pH band, 6 to 8, which almost never happens here. Two publish the same lifespan. Two publish the same lower lethal temperature to a decimal. The disagreements on this record are about how much water it needs and how big it finally gets, and nothing else.
The second of those turns out to be a disagreement between reference sources rather than care sheets. The Florida Museum of Natural History gives a maximum of 33 cm and about 1.1 kg. Wikipedia reports specimens grown to about 70 cm and 9 kg. Station 06 sets the two out rather than splitting them.
Why this record was written now
- The gap
- It was next in the freshwater fish queue at 23,000 searches a month, and this silo held one cichlid, the angelfish, against four still queued.
- What it changes
- The largest minimum tank on the site goes from 55 gallons to 75, the site gains its first per species filtration figure, and it gains a second pairing that no tank can fix.
- What it does not
- Every field is filled, and one of them should not be trusted as much as the rest: the hardness figure has a single source and no second figure to check it against.
Oscar fish tank size, and the argument about two of them
Three of our sources give a tank figure and they do not disagree much about one oscar. They disagree completely about two, which is the more useful question, because almost nobody who wants an oscar wants exactly one.
| Source | One oscar | More than one | What else it states |
|---|---|---|---|
| Aquarium Co-Op | 75 gal | 90 to 100 gal | 5 to 6 feet of length for two, and swimming space to turn around |
| Aquarium Source | 55 gal | Plus 25 gal each | Stated as the ideal minimum rather than a floor |
| Aquarium Science | No floor | 50 gal for a couple | Approves a 64 gal of 4 ft by 17 in; calls four in 100 gal unpredictable |
| Florida Museum | Not stated | Not stated | Slow moving water with cover from sunken branches and logs |
| Wikipedia | Not stated | Not stated | A food fish in local markets in its native range |
| Tropical Fish Hobbyist | Not stated | Not stated | A feeding schedule by size class instead |
- What this record carries. 75 gallons, because Aquarium Co-Op does not merely publish it, it argues for it against the lower number: while some people say that a 55 gallon tank is the minimum for one oscar, it believes 75 is better so the fish has more swimming space to turn around.
- The disagreement about two is a factor of two. Aquarium Co-Op wants at least 90 to 100 gallons and 5 to 6 feet of length. Aquarium Science calls a 50 gallon acceptable for a couple. Both are talking about two adult oscars in one box.
- One source refuses to give a floor and says why. Asked whether four full grown oscars fit in 100 gallons, Aquarium Science answers that the outcome is unpredictable because oscars are individuals. That is a real position and this record prints it rather than treating silence as agreement.
- Length appears once and matters. Only Aquarium Co-Op states a tank length, 5 to 6 feet for two fish, and Aquarium Science only ever approves a tank by its dimensions rather than its volume, in that case 4 feet by 17 inches. A 12 inch fish that has to turn around is a length problem before it is a volume problem, the same way the angelfish is a height problem.
- What our own tool does with it. The stocking calculator answers for 5, 10, 20 and 29 gallon tanks. At 75 gallons this is the record furthest outside that range, so the tool refuses it at every size and prints the figure that refused it.
The first filtration figure on this site that is per fish
Media measured in cubic feet
Until this record, every page here said the same thing about filters: our sources publish tank sized rules and nobody publishes a figure per species. Aquarium Science publishes one.
For a single 12 inch oscar it asks for one half to one cubic foot of foam, pot scrubbers or K1, which it puts at one to two canister filters of a named model. For inferior media such as ceramic rings it asks for two to four cubic feet, or four to eight of the same canisters.
That is a figure about the fish rather than about the water it sits in, and it is the only one of its kind we have found. Aquarium Co-Op states the reason without a number: as a big fish they create a lot of waste and need adequate filtration, with the type of filter mattering less than whether the current is gentle and the media can handle the bioload.
What it does not change
The calculator still returns no bioload figure and no filter rating, and this record is the reason to say why precisely rather than loosely. A media volume for one 12 inch oscar cannot be turned into a percentage for a 1 inch pea puffer or a 40 mm cherry shrimp, and nothing we have read publishes the curve between them.
So the tool's refusal stands on a narrower claim than before: not that nobody publishes a filtration figure per species, but that nobody publishes one for the species and volumes it covers. Our about page carries that claim as a row you can check, and it has been corrected to say this.
The other figure in this area belongs to a different record. PetMD gives five tank turnovers an hour for a goldfish tank, which is a rule about the tank. This one is a rule about the animal.
The full record
| Field | Recorded | Where it comes from |
|---|---|---|
| Minimum tank | 75 gal | Aquarium Co-Op, which states the case against the lower figure: while some people say that a 55 gallon tank is the minimum for one oscar, it believes 75 gallons is better so that they have more swimming space to turn around. Aquarium Source publishes that 55 gallon minimum, and adds at least 25 gallons for each new oscar. Aquarium Science goes lower still and gives no floor at all: it calls a 50 gallon acceptable for a couple of oscars and approves a 64 gallon of 4 feet by 17 inches, while answering a question about four full grown oscars in 100 gallons by saying the outcome is unpredictable because the fish are individuals. The sharpest disagreement is not the single fish figure but the pair: Aquarium Co-Op asks for 5 to 6 feet of length and at least 90 to 100 gallons for two, where Aquarium Science accepts 50. |
| Temperature | 75 to 80 °F | Aquarium Source. Aquarium Co-Op gives 74 to 80 and calls the fish very hardy, so the two bands share 75 to 80. Aquarium Science states no figure at all and argues the point instead: oscars do fine in a wide range of water hardness, pH and temperatures. The only figure below the bands is a limit rather than a preference, and two sources publish it independently: Wikipedia and the Florida Museum both give a lower lethal temperature of 12.9 °C, about 55 °F. |
| pH | 6.0 to 8.0 | Aquarium Co-Op and Aquarium Source publish the same band, 6 to 8, which almost never happens on this site. Aquarium Science publishes nothing and states that the fish is nowhere near as sensitive to ammonia, nitrite or nitrate as hobbyists seem to think, which is a claim about tolerance rather than a target. |
| Hardness | 215 to 268 ppm | Aquarium Source alone, as 12 to 15 dH, converted here at about 17.9 ppm per degree. The floor of 215 ppm is the highest on this site and only the nerite snail matches it, so the oscar and the snail are the only two records here that refuse soft water. Three records reach higher at the top, the guppy furthest at 536 ppm. No second source publishes a figure for this species to check it against: Aquarium Science says only that oscars do fine in a wide range of hardness. Read it as one source's number, not as a consensus. |
| Adult size | 10 to 12 in, captive | Aquarium Co-Op and Aquarium Source both give 10 to 12 inches in captivity, and Aquarium Co-Op adds or more. Beyond that the sources separate by a factor of two. The Florida Museum of Natural History gives a maximum of 33 cm, 13 inches, and a maximum weight of about 1.1 kg. Wikipedia reports specimens grown to about 70 cm, 28 inches, and 9 kg. Aquarium Source puts the wild figure between them, saying the fish can exceed the 14 to 15 inch mark. A shop juvenile is 2 to 3 inches, per Aquarium Co-Op. |
| Diet | Predatory omnivore, and it eats fish | Tropical Fish Hobbyist states that live fishes and insects constitute approximately 90 percent of the overall diet of wild oscars, with fruits, nuts, shrimps and snails taken seasonally. Wikipedia agrees on the composition and specifies that most fish eaten in the wild are relatively sedentary catfish. The Florida Museum lists smaller fishes, crustaceans, gastropods and aquatic insects or insect larvae. In the aquarium, Aquarium Co-Op names pellets, freeze dried krill, crickets and mealworms, and gives the portion as a slightly rounded belly that is not too concave or swollen. Aquarium Science gives an amount instead: once a day, about a level teaspoon per oscar, or two eyeballs worth of dry pellets. |
| Water column | All levels | Ours, from three sources describing three different parts of the tank. Aquarium Co-Op asks for enough water that the fish has swimming space to turn around. Aquarium Source says they love to scrounge through your substrate in an attempt to dig up some food. The Florida Museum places them in slow moving waters that afford them cover in the form of sunken branches and logs. That is the whole box, which is why this is the second record here that does not fit one of the four layers. |
| Lifespan | 10 to 20 years | Aquarium Co-Op and the Florida Museum of Natural History publish the same band, and the museum states it of captive fish specifically. Aquarium Source is shorter and more precise about the tail: an average of 10 to 13 years, with an oscar with great genetics and good care living to be over 15. Wikipedia gives a reproductive span rather than a lifespan, saying the species continues to reproduce for 9 to 10 years. |
| Growth rate | Two thirds of adult size in 6 to 12 months | Aquarium Co-Op, which adds that development then slows. It is only the third growth figure on this site, after the cherry shrimp and the goldfish, and it is the one that explains why this fish is so often rehomed: the 2 to 3 inch juvenile in the shop tank is 7 or 8 inches within a year. |
The same nine fields for every animal on this site are in the A to Z index.
Where our sources disagree
Every record here names a disagreement. This one has two, and they are about opposite ends of the same fish: how much water it needs, and how large it actually gets.
The Florida Museum of Natural History
The oscar is a large cichlid reaching lengths of 33cm and a maximum weight of approximately 1.1kg. Captive oscars commonly live 10-20 years. The mean lower lethal temperature for this species is 12.9 °C. A single spawning may consist of as many as 1000 to 2000 eggs.
Wikipedia
A. ocellatus examples have been reported to grow to about 70 cm (28 in) in length and 9 kilograms (20 lb) in weight. The lower lethal limit for the species is 12.9 °C (55.22 °F).
What we record: we carry the captive figure both care sources agree on, 10 to 12 inches, and print the two reference maxima side by side rather than choosing between them. They are not the same kind of claim: a museum profile stating a maximum length is not the same as an encyclopedia reporting the largest specimens anyone has recorded.
Both figures are useful and neither belongs in the row. The two sources agree exactly on the one figure a keeper can act on, the lower lethal temperature of 12.9 °C, which is the one figure the museum and the encyclopedia state identically.
The water figures agree, which is new here
On most records this site holds, the water figures are where the sources fall out. On this one they very nearly match, and the exception is the field with only one source behind it.
Aquarium Source. Aquarium Co-Op gives 74 to 80 and calls the fish very hardy.
Both publishing sources give the same band, which has happened on one other record here.
12 to 15 dH at Aquarium Source, and nothing to check it against.
- The hardness figure is the one to be careful with. 12 to 15 dH puts the floor at 215 ppm, the highest floor on this site, matched only by the nerite snail. Three records reach higher at the top, the guppy furthest at 536 ppm, so this is not the hardest water we hold; it is the water with the least room below it, and it is asked for on behalf of a fish from the Amazon. One source publishes it, no source contradicts it, and no source confirms it. It is printed with that caveat attached rather than left to look like a consensus.
- One source argues that none of this matters much. Aquarium Science states that oscars do fine in a wide range of water hardness, pH and temperatures, and that they are nowhere near as sensitive to ammonia, nitrite or nitrate as hobbyists seem to think. It is the same source that asks for a cubic foot of filter media per fish, so the position is not that water quality is unimportant.
- The two reference sources match on the cold limit. Wikipedia and the Florida Museum both give a lower lethal temperature of 12.9 °C, about 55 °F. It is the one figure those two state identically, on a record where they disagree about maximum size by a factor of two, and it is a limit rather than a target.
- Where that leaves the tank mates. A floor of 75 °F is the second highest on this site, after the angelfish at 78. It sits one degree above the goldfish ceiling of 74, which is station 07.
How big does an oscar get? Two references, twice the answer
The captive figure is settled and the wild figure is not. Both care sources give the same 10 to 12 inches for a fish in a tank. Beyond that the numbers separate, and the two that separate furthest are the two least likely to be wrong by accident.
| Figure | Value | What it describes | Source |
|---|---|---|---|
| In a shop | 2 to 3 in | The juvenile people buy | Aquarium Co-Op |
| Adult, captive | 10 to 12 in | Or more | Aquarium Co-Op |
| Adult, captive | 10 to 12 in | Stated as the average | Aquarium Source |
| Wild | Over 14 to 15 in | Can exceed | Aquarium Source |
| Maximum length | 33 cm (13 in) | A museum profile's maximum | Florida Museum |
| Maximum weight | 1.1 kg (2.4 lb) | The same profile | Florida Museum |
| Reported length | 70 cm (28 in) | Reported specimens | Wikipedia |
| Reported weight | 9 kg (20 lb) | Reported specimens | Wikipedia |
| Weight at 12 in | 0.75 to 1 lb | The author's estimate | Aquarium Science |
| Weight scaling | 8 times | A 12 in fish against a 6 in fish | Aquarium Science |
| Growth | Two thirds in 6 to 12 months | Then development slows | Aquarium Co-Op |
- 33 cm against 70 cm is not a rounding. One is a museum stating a maximum length for the species; the other is an encyclopedia reporting the largest specimens anyone has recorded. Those are different claims and this record prints both rather than averaging two numbers that are twice each other.
- The weight figures can be read against each other. Aquarium Science estimates a 12 inch oscar at three quarters of a pound to one pound, and notes a reader disputing that with two and a half. The Florida Museum's maximum weight for the species is 1.1 kg, which is 2.4 pounds. The museum figure sits with the reader rather than the author, and we are printing that as arithmetic rather than as a verdict.
- The growth figure is the one that costs people money. Two thirds of adult size in the first 6 to 12 months means the 3 inch fish is 7 or 8 inches within a year. It is the third growth rate on this site, after the cherry shrimp and the goldfish, and the only one that describes a fish outgrowing its tank.
- The varieties have no figures. Wikipedia names albino, leucistic and xanthistic forms and long finned varieties. Not one of our sources publishes a separate size, tank or water figure for any of them, so this record treats them as one fish and says so.
Oscar tank mates, and two of our own records ruled out by name
This is the shortest tank mate section on the site, and the reason is in the diet row. Tropical Fish Hobbyist states that live fishes and insects constitute approximately 90 percent of the overall diet of wild oscars. A fish with that diet in a tank with small fish is not sharing the tank.
| Record | Verdict | The figure or statement that decides it |
|---|---|---|
| Goldfish | Refused twice | Aquarium Source names it: small fish like goldfish or guppies will be toast. And the bands do not touch, 75 to 80 against 68 to 74. |
| Guppy | Named no | The same sentence names guppies. Our record has them at 2 to 2.5 in. |
| Ember tetra | No | Aquarium Co-Op: do not keep them with nano creatures. Ours are 15 to 20 mm. |
| Cherry shrimp | No | Wikipedia lists shrimp in the wild diet. Ours are 30 to 40 mm. |
| Nerite snail | No | The Florida Museum lists gastropods in the natural diet, and Wikipedia lists snails. |
| Pea puffer | No | 1 inch, and a fin nipper on our record. Both halves fail. |
| Otocinclus | No | 35 to 50 mm on our record, and easily out-competed for food by its own description. |
| Kuhli loach | No | 90 to 100 mm and it hides in the substrate the oscar digs through. |
| Betta | No | 60 to 70 mm, and long finned in a tank with a fish that rearranges its environment. |
| Corydoras | No | 1 to 3 in. Wikipedia states that most fish eaten by oscars in the wild are relatively sedentary catfish. |
| Angelfish | Not answered | Aqueon names other medium sized South American cichlids as suitable and Aquarium Co-Op says the same, but no source names this pairing and our angelfish record is 6 in against 12. |
- Ten of eleven records are refused, and the eleventh is not answered. That is the honest state of it. Every no above rests on a size our own record publishes or a food item our sources name, not on a general warning about big cichlids.
- What our sources do name as suitable is not on this site. Aquarium Co-Op names bigger peaceful fish like silver dollars, certain plecos and other medium sized South American cichlids. Aquarium Source names a longer list of the same kind: bichirs, Jack Dempsey, green terrors, silver dollars, arowanas, plecos. We hold records for none of them, and pretending otherwise would be the easiest way to make this page look more useful than it is.
- The goldfish refusal is the one worth reading twice. It is refused as food and refused on temperature, which no other pairing here manages, and Tropical Fish Hobbyist adds a third reason nobody expects: it warns about disease transmission from feeder fish, goldfish especially. Our own goldfish record is a care record for an animal another record here lists as a hazard.
- The angelfish row is a gap, not a verdict. Two sources say medium sized South American cichlids are suitable and the angelfish is one. Neither names it, and a 6 inch fish beside a 12 inch predator is not something this site will wave through on a category. The tank mates grid marks it unanswered.
Feeding oscar fish, by size class rather than by clock
Two sources give a feeding schedule and they use different axes. Tropical Fish Hobbyist changes the frequency as the fish grows. Aquarium Science gives an amount and leaves the frequency alone. Aquarium Co-Op gives neither and describes the fish instead.
| Source | How often | How much |
|---|---|---|
| TFH, juveniles at 1.5 to 3 in | At least twice daily | Until the bellies are slightly distended |
| TFH, subadults at 4 to 6 in | Daily, alternating one and two feeds | Not stated |
| TFH, adults at 7 to 8 in and up | Every other day, twice weekly two or three feeds | Not stated |
| Aquarium Science | Once a day | About a level teaspoon per oscar, or two eyeballs worth of dry pellets |
| Aquarium Co-Op | Not stated | A slightly rounded belly, not too concave or swollen |
- The two amounts are not in conflict, they are in different units. A level teaspoon and a slightly rounded belly are the same instruction expressed by a measuring spoon and by looking at the fish. Two eyeballs worth is the third form of it and the most quoted in the hobby.
- Feeder fish carry a warning from the source that recommends them. Tropical Fish Hobbyist treats live feeder fish as a food and states they should never be the exclusive diet, then names the risk: disease transmission, with goldfish especially. It also names foods that are not obvious, including small crickets and mealworms, and frozen peas.
- What not to feed is as specific as what to feed. The same source rules out crisps and flakes because the particles foul the water, insects exposed to chemicals or insecticides, and small frozen foods such as brine shrimp and bloodworms for anything but the smallest juveniles.
- The wild diet is the reason for all of it. Approximately 90 percent live fishes and insects, per Tropical Fish Hobbyist, with fruits and nuts seasonally, which Wikipedia and the Florida Museum both confirm. Our breeding topic holds the spawning figures: the museum records 1000 to 2000 eggs in a single spawning, hatching in 3 to 4 days.
A fish that rearranges the room
Plants and decor
Two sources describe the same behavior in different words. Aquarium Co-Op says oscars like to rearrange their environment and uproot plants. Aquarium Source says they love to scrounge through your substrate in an attempt to dig up some food.
Aquarium Source is also the only source on this site to answer the question that follows, and it answers it with a plant: hornwort, as a floating option, because it will not be damaged by any of the digging oscars do.
Hornwort now has a record of its own, and it does not settle this. Aquarium Breeder names oscars among the fish to keep away from hornwort because they can damage the plant, against Aquarium Source recommending it here for exactly the opposite reason. Both statements are printed on the plant record, and neither this record nor that one turns one of them into a verdict.
The same publisher has now been read on all three of our plant records, and the oscar is on its harmful list for two of them. Aquarium Breeder says the oscar will devour java moss, naming it with the red devil and the siamese algae eater, and it says java fern withstands oscars because they find the hard leaves unappetizing. That is the clearest thing any source says about this fish and plants: it is not the fish that decides, it is the leaf.
Health, and the one condition both care sources name
Aquarium Co-Op and Aquarium Source both name hole in the head disease, which Aquarium Source describes as one or two small holes in the head. Aquarium Co-Op frames it as a reason to keep the immune system healthy rather than as a treatment.
This site does not print treatments, for the same reason the goldfish record transcribes a veterinary list without adding one: a care record is not a diagnosis. What it can do is say that two of our six sources independently name the same condition for this species, which is worth more than either of them saying it alone.
The water and health topic collects what our sources say about keeping a tank stable, including the disagreement about what a safe ammonia reading is. Aquarium Science's position on this record, that oscars are nowhere near as sensitive to ammonia, nitrite and nitrate as hobbyists think, belongs in that argument rather than in this row.
What this record will not answer
Four things about oscars our six sources do not settle.
- How hard the water should be. One source publishes 12 to 15 dH and nothing checks it. It is on the record with that stated, and it is the only field here we would flag before acting on. Its floor of 215 ppm is the highest on the site, which is a strange thing to find on an Amazon fish and a reason to want a second source rather than to trust the first.
- How large the fish actually gets. A museum says 33 cm, an encyclopedia reports 70 cm. Both are printed. The captive figure, 10 to 12 inches, is the one two sources agree on and the one the record carries.
- Whether an oscar can live with our angelfish. Two sources say medium sized South American cichlids are suitable tank mates and neither names this pairing. A 6 inch fish next to a 12 inch predator is not a verdict we will infer from a category.
- What a rainbow oscar or a red oscar is. Both are searches people make and neither phrase appears in any of our six sources. Wikipedia names albino, leucistic and xanthistic forms and long finned varieties, and gives no separate figures for any of them. Those are descriptions of pigment, and matching them to a shop name on the strength of both being about color is the kind of guess this site does not print. If a source publishes the mapping, it will go here.
Oscar fish questions, answered from the record
What size tank does an oscar fish need?
This record carries 75 gallons for one fish, from Aquarium Co-Op, which argues for it against the lower figure: while some people say a 55 gallon tank is the minimum for one oscar, it believes 75 gallons is better so they have more swimming space to turn around. Aquarium Source publishes 55 as its ideal minimum and adds at least 25 gallons for each additional oscar.
For two fish the sources split completely. Aquarium Co-Op wants 5 to 6 feet of length and at least 90 to 100 gallons. Aquarium Science calls a 50 gallon acceptable for a couple of oscars and refuses to give a floor at all, on the grounds that oscars are individuals and the outcome is unpredictable. Station 02 prints every figure.
How big do oscar fish get?
10 to 12 inches in captivity, which Aquarium Co-Op and Aquarium Source both publish, with Aquarium Co-Op adding or more. That is the figure this record carries.
The wild figure is disputed between two reference sources. The Florida Museum of Natural History gives a maximum of 33 cm, 13 inches, and about 1.1 kg. Wikipedia reports specimens grown to about 70 cm, 28 inches, and 9 kg. Aquarium Source sits between them, saying the fish can exceed 14 to 15 inches. Station 06 prints all eleven size and weight figures with what each one describes.
How fast do oscars grow?
Aquarium Co-Op states that oscars achieve two thirds of their adult size within the first 6 to 12 months, and that development then slows. Set that beside the size they are sold at, 2 to 3 inches, and the fish in the shop tank is 7 or 8 inches within a year.
It is the third growth figure on this site, after the cherry shrimp and the goldfish, and the only one that describes a fish outgrowing the tank it was bought for.
How long do oscar fish live?
10 to 20 years. Aquarium Co-Op and the Florida Museum of Natural History publish that same band, and the museum states it of captive fish specifically. Aquarium Source is a little shorter, giving an average of 10 to 13 years with an oscar of great genetics and good care living to be over 15.
Wikipedia gives a different kind of figure: the species continues to reproduce for 9 to 10 years, which is a reproductive span rather than a lifespan and is not the same claim.
Are oscar fish aggressive?
Aquarium Co-Op says they are not overly aggressive except during spawning seasons. Aquarium Source says they have the potential to be quite aggressive and territorial. Both are true of the same fish and neither is the reason the tank mate list is short.
The reason is the diet. Tropical Fish Hobbyist states that live fishes and insects make up approximately 90 percent of the wild diet, and Aquarium Source puts the consequence bluntly: small fish like goldfish or guppies will be toast if kept in a tank with oscars. An oscar does not have to be aggressive to eat a guppy.
What can live with an oscar fish?
Nothing this site holds a record for. Station 07 runs our sources' rules against all eleven other records and ten of them are refused on a size our own record publishes or a food item our sources name. The eleventh, the angelfish, is not answered because no source names the pairing.
What our sources do name is bigger, peaceful fish: silver dollars, certain plecos and other medium sized South American cichlids at Aquarium Co-Op, with bichirs, Jack Dempsey, green terrors and arowanas added by Aquarium Source. We hold no records for any of those, so this page can tell you the category and not the animal.
Can oscars live with goldfish?
No, and this pairing is refused three separate ways, which no other pairing on this site manages. Aquarium Source names it: small fish like goldfish or guppies will be toast. The temperature bands do not touch, since this record carries 75 to 80 °F and our goldfish record carries 68 to 74. And Tropical Fish Hobbyist warns about disease transmission from feeder fish, goldfish especially.
It is the second pairing here that no tank size can fix, after the angelfish and the goldfish.
How often should you feed an oscar?
It depends on the size of the fish, and Tropical Fish Hobbyist is the only source that says so. Juveniles of 1.5 to 3 inches are fed at least twice daily until their bellies are slightly distended. Subadults of 4 to 6 inches are fed daily, alternating one feed and two. Adults of 7 to 8 inches and up are fed every other day, with two or three feeds twice a week.
Aquarium Science gives an amount rather than a schedule: once a day, about a level teaspoon per oscar, or two eyeballs worth of dry pellets. Aquarium Co-Op gives neither and says to adjust the portion so the belly is slightly rounded, not too concave or swollen.
Do oscars eat plants?
They uproot them, which our sources treat as a different problem. Aquarium Co-Op says oscars like to rearrange their environment and uproot plants. Aquarium Source describes them scrounging through the substrate to dig up food. Neither of those two describes an oscar eating a plant, though our java moss record carries a third source that does, saying oscars will devour that moss. Compare our goldfish record, where Wikipedia states plainly that goldfish eat live plants.
Aquarium Source is the only source on this site that answers the question with a plant: hornwort, floating, because the digging will not damage it. Our hornwort record publishes 59 to 86 °F, which contains this record entirely, and it is one of three plants Aquarium Store Depot names as tough enough for a fish that chews, on the page behind our freshwater puffer fish guide.
What water parameters do oscars need?
Temperature 75 to 80 °F, which is the band both publishing sources share, and pH 6 to 8, which they publish identically. That level of agreement is rare on this site.
Hardness is the exception and it is flagged on the record. Aquarium Source alone gives 12 to 15 dH, about 215 to 268 ppm. That floor of 215 is the highest on this site, matched only by the nerite snail, although three records reach higher at the top. Aquarium Science publishes no water figures and argues instead that oscars do fine in a wide range of hardness, pH and temperature.
What filter does an oscar need?
Aquarium Science publishes the only per fish filtration figure this site has found: for one 12 inch oscar, one half to one cubic foot of foam, pot scrubbers or K1, which it puts at one to two canister filters of a named model. For inferior media such as ceramic rings it asks for two to four cubic feet instead.
Aquarium Co-Op states the requirement without a number, saying that as a big fish they create a lot of waste and need adequate filtration, with the type mattering less than a gentle current and enough media for the bioload. Station 03 explains why our calculator still refuses to publish a bioload figure.
Where do oscar fish come from?
The Amazon basin, and the oscar fish habitat our sources describe is specific: the Florida Museum places them in slow moving waters that afford them cover in the form of sunken branches and logs. Wikipedia gives the range as Brazil, Colombia, Ecuador, Guyana, French Guiana, Suriname, Peru and Venezuela, along the Amazon and the Ica, Negro, Solimoes and Ucayali river systems. The Florida Museum is narrower: strictly freshwater, restricted to the Rio Ucayali drainage and the upper Amazon of Peru and Brazil.
Two other facts sit oddly beside the aquarium trade. Wikipedia records that in tropical South America the species is often sold as a food fish in local markets, and the Florida Museum records breeding populations established in no less than six Florida counties from a deliberate stocking by aquarium fish farms in the late 1950s, including inside Everglades National Park.
Where does this record disagree with the rest of the site?
In four places. Its 75 gallon minimum is the largest here and sits far outside the volumes the calculator answers for. Its hardness figure has the highest floor of any record here and one source behind it. It is the first record to carry a filtration figure stated per fish. And its tank mate section refuses ten of eleven records, which is the most on the site.
The full index lists every record we hold, the freshwater fish silo lists what is queued, and the method page says what happens here when a new record contradicts an old claim.
Three sources now recommend a tank mate for this fish that our own rows can barely support. Aquarium Source, Everything Fishkeeping and Aquarium Store Depot all name the oscar as a companion for the fish on our flowerhorn record, and Aquarium Store Depot asks for 215 gallons minimum before any tank mate goes in at all. This record carries 75 to 80 °F and that one carries 80 to 86, so the two published bands meet at a single figure: 80. A pairing three sources recommend and one degree of water allows is printed on our tank mates grid as a caution rather than a refusal, with the arithmetic beside it. The two records also share the largest-fish problem from opposite ends: this one is 10 to 12 inches in 75 gallons, and that one is 9.5 to 16 inches in 70.
What an oscar tank needs and a community tank does not
Three requirements our sources state that a gallon figure does not carry.
- Length, not just volumeAquarium Co-Op: 5 to 6 feet for two
- Filter media measured in cubic feethalf to one cubic foot per 12 inch fish
- Decor you can afford to have movedthey rearrange it and uproot plants
Every item our records ask for is gathered on the tank setup topic.
Nothing here is a paid link. It is the shortfall between what this record asks for and what a boxed kit contains.
How this record was compiled
- By
- Verified
- Sources
Aquarium Co-Op, oscar fish care guide, Aquarium Source, Aquarium Science, oscars, Florida Museum of Natural History, Tropical Fish Hobbyist, feeding oscars and Wikipedia, Oscar (fish)
- Conflicts
Printed above: a museum gives a maximum of 33 cm and an encyclopedia reports 70 cm
- Not recorded
A hardness figure with a second source behind it, and any figure at all for the albino, leucistic, xanthistic and long finned forms our sources name