Oscar
Species Freshwater fish Astronotus ocellatus
Written with AI assistance, not yet checked by a person. Treat the details as a starting point and confirm important decisions with a vet or a breeder.
Overview
A large South American cichlid that reaches 25-35 cm and lives 10-15 years or more. It recognises its keeper, but needs a tank of at least 300 L for one adult, strong filtration and big weekly water changes, and it eats any fish that fits in its mouth. A long, costly commitment, not a fish for a community tank.
Native to the Amazon basin (Brazil, Peru, Colombia and neighbouring countries), where it is also a food fish. Red, tiger, albino and long-finned forms are bred for the aquarium trade. Small juveniles are sold at a few centimetres and grow fast.
- Purchase price
- Pet quality €5–20
- Care difficulty
- Intermediate
- Long, flowing fins
- No
- Adult body length
- 25–35 cm
- Good with other pets
- Activity pattern
- Diurnal
- Temperament
- Intelligent and interactive: it learns feeding routines, "begs" at the glass and rearranges decorations. Territorial, especially when breeding, and predatory towards smaller fish. Breeding: a pair cleans a flat stone, lays several hundred eggs and guards the young.
- Temperament
- Semi aggressive
- Schooling fish
- No
- Nips the fins of other fish
- No
- Keep only one per tank
- No
Health and common problems
These are common issues for this animal, not a diagnosis. If you are worried about your animal, see a vet.
Ammonia and nitrite poisoning
Frequency: Uncommon Emergency
Fish waste turns into ammonia and nitrite, which are toxic. In a new tank that is not cycled yet, an overstocked tank, or after the filter bacteria are destroyed, levels rise fast. This is the most common cause of death of new aquarium fish.
- Signs to look for
- Gasping at the surface, red or dark gills, lethargy, clamped fins, sudden deaths, cloudy water.
- Prevention
- A large fish produces a lot of waste: filter for at least 3-4 times the tank volume per hour and never skip water changes.
- When to see a vet
- If fish keep dying after the water tests are normal again. Prevention is cycling the tank for several weeks before adding fish.
- First aid
- Test the water at once, do a large water change (with conditioned water at the same temperature), stop feeding for a day and do not clean the filter in tap water.
Ich (white spot disease)
Frequency: Uncommon Moderate
A common parasite of aquarium fish that shows as small white dots. It spreads fast in a tank and is worse after stress or cold shocks.
- Signs to look for
- White dots on skin and fins, rubbing on objects, clamped fins, fast breathing.
- How to handle it
- Treat the whole tank with an ich product made for aquariums, following the label; remove activated carbon from the filter during treatment.
- Prevention
- Quarantine new fish for 2-4 weeks and avoid sudden temperature drops.
- When to see a vet
- If fish keep dying, or you are not sure which disease it is.
- First aid
- Raise the temperature slowly within what your fish tolerate and follow the instructions of an ich treatment made for aquariums.
Obesity
Frequency: Uncommon Mild
Too much body fat strains joints and the heart, and shortens life. It usually comes from extra food, treats and too little exercise.
- Signs to look for
- Ribs hard to feel, no visible waist, getting tired quickly, weight gain over months.
- Prevention
- Adults need food only once a day or every other day; avoid fatty meat.
- When to see a vet
- When weight rises despite a normal diet, or before starting a strict diet.
- First aid
- Measure portions, cut treats, and increase exercise slowly.
Hole-in-the-head disease
Frequency: Common Moderate
Pits and erosions appear on the head and along the lateral line, mainly in large cichlids such as the oscar. Poor water (high nitrate), a one-sided diet and a parasite (Hexamita) are linked to it.
- Signs to look for
- Small pits on the head that grow into holes, white stringy droppings, loss of appetite.
- Prevention
- Large weekly water changes (30-50 %) to keep nitrate low and a varied, good-quality diet.
- When to see a vet
- When pits appear, before they grow. An aquatic vet can decide on medication.
- First aid
- Increase water changes to lower nitrate and feed a varied, good-quality diet.
Care and maintenance
-
30 % water change
every week
Siphon about 30 % of the water from the bottom and refill with conditioned tap water at the same temperature.
-
Test the water
every week
Check ammonia, nitrite and nitrate (and pH); act on any ammonia or nitrite reading.
-
Rinse the filter sponge
every month
Squeeze the sponge in a bucket of old tank water, never under the tap: tap water kills the useful bacteria. Replace media only in parts.
-
Count the fish and check the temperature
every day
At feeding time count the fish, look for clamped fins, spots or heavy breathing, and read the thermometer. Remove uneaten food after a few minutes.
-
Clean the glass and trim plants
every 2 weeks
Wipe algae from the front glass and remove dead leaves.
Sign in to add these tasks to your reminders for your Oscar.
What it costs
This is an estimate, not a quote. It multiplies typical amounts by typical prices in Serbia. Your real costs depend on the shops, the vet and the animal. Change the assumptions below to match your situation.
Who it gets along with
Worked out from the traits of this animal. Individual animals differ, and introductions should always be slow and supervised.
Avoid keeping with
-
Cats
Based on the typical temperament of Oscar (1/5). -
Dogs
Based on the typical temperament of Oscar (1/5). -
Small pets
Based on the typical temperament of Oscar (1/5). -
Birds
Based on the typical temperament of Oscar (1/5). -
Fish
Based on the typical temperament of Oscar (1/5).
Not enough information about: children, seniors, strangers.
Notable cases
- Oscar (Be careful with): One oscar, or a pair that has bonded on its own, in 450 L or more; two unpaired adults often fight.
Set-up and food
- Minimum group size
- 1 animals
- Water temperature
- 22–28 °C
- pH
- 6–8
- General hardness (GH)
- 5–20 dGH
- Minimum tank size
- One animal 300 l
- Swimming level
- Mid
- Needs live plants
- No
- Needs hiding places
- No
- Water flow
- Moderate
- Jumps, needs a tight lid
- Yes
- Diet type
- Carnivore
Oscar, 400 L
400 L About €900 (estimate)
A 400 L tank on a strong stand with a canister filter, two heaters, a heavy lid, sand and large smooth stones or roots fixed in place; for one oscar or a bonded pair with very robust company.
- Aquarium tank – 400 L with stand
- Aquarium filter – canister
- 2 × Aquarium heater – 2 x 200 W
- Aquarium thermometer
- Aquarium lid
- Aquarium light
- Fine sand substrate
- Water conditioner
- Water test kit
- Gravel siphon and bucket
Equipment
Required
-
Aquarium filter
Keeps the water clean and moving and holds the useful bacteria; sized to the tank. A canister or large hang-on filter rated for at least 3-4 times the tank volume per hour; cycle the tank before adding the fish. -
Aquarium heater
Holds the water at the right temperature; a thermostat model is the norm. -
Aquarium lid
Stops fish that jump and slows evaporation. Oscars can jump when startled; a heavy, tight lid. -
Aquarium tank
at least 300 L
Glass or acrylic tank on a stand that carries the full weight (about 1 kg per litre). -
Aquarium thermometer
Checks that the heater works; read it daily. -
Water conditioner
Removes chlorine and chloramine so tap water is safe for fish. -
Water test kit
Drop tests or strips for ammonia, nitrite, nitrate, pH and hardness. Ammonia, nitrite and nitrate; daily during cycling, weekly afterwards.
Recommended
-
Aquarium light
LED lighting on a timer, about 8 hours a day; stronger light is needed for demanding plants. -
Gravel siphon and bucket
For water changes and cleaning the substrate; keep the bucket only for the aquarium.
Food
- Frozen bloodworms – For juveniles, a few times a week.
- Large cichlid pellets – As much as is eaten in about two minutes. Juveniles 2-3 times a day, adults once a day.
Never feed: Live feeder fish. Full toxic foods checker
Breeding
- Breeding type
- Egg depositor
Breeding is a big responsibility. Many animals in shelters are waiting for a home; ask a vet and a breeders association before you plan a litter.
Legal
Check your local law. Rules about keeping, importing and selling animals differ between countries and regions and change often. What is written here may be out of date; ask your local authority before you buy or adopt.
No specific legal rules are recorded for this animal.
General information, not veterinary advice. Every animal is an individual. Typical values and costs are estimates. Talk to a vet, a breeder or a shelter before you decide, and see a vet if your animal is unwell.