How to Care for Goldfish: A Comprehensive Guide for Australian Enthusiasts

Most people end up here for the same reason: a goldfish has arrived in the house, and the tank (or pond) suddenly feels too small, too cloudy, or too hard to keep stable. With goldfish, the consequences are usually slow and quiet—waste builds, water chemistry drifts, and health problems follow.

What helps is a simple set of checks: enough water volume, strong filtration, a fully cycled tank, and a feeding routine that doesn’t overwhelm the system. Below is a practical, Australia-focused guide that keeps the details grounded and the decisions clear.^{1, 2}

Goldfish in Australia: pets, and also potential pests

Goldfish (Carassius auratus) were brought to Australia as ornamental fish and are now established in many waterways, particularly across the southern half of the country.^{3, 4}

That’s why the most important rule of goldfish keeping in Australia is also the simplest: never release aquarium fish, plants, or water into drains, creeks, rivers, or dams. If you can’t keep a fish, rehome it through a pet shop, another keeper, or a local aquarium society—don’t “set it free”.^{1, 2}

A brief history (and why they look so different)

Goldfish were domesticated from carp-like ancestors in China, then shaped by centuries of selective breeding into the varieties seen today—streamlined commons and comets, and round-bodied “fancy” types with ornate fins and altered head shapes.⁶

Those body shapes aren’t just cosmetic. Rounded fancy goldfish tend to be slower swimmers and can be more prone to buoyancy and fin issues, which makes stable water quality and gentle tank design more important.

Behaviour: calm, busy, and best with their own kind

In a settled tank, goldfish spend much of the day cruising, picking at surfaces, and sifting through the bottom for edible scraps. It’s normal to see brief jostling at feeding time, especially in groups.

They’re usually safest kept with other goldfish. Many tropical community fish need warmer water, and small fish may be bullied or accidentally eaten once a goldfish is big enough to fit them in its mouth.

Tank setup and environment

Tank size: think in terms of adult fish

Goldfish are often sold small, but they don’t stay that way. In Australia, wild and escaped fish can reach large sizes, and even in home care a well-fed goldfish can outgrow a “starter” setup quickly.^{1, 4}

• Avoid bowls. They’re difficult to filter and unstable for temperature and water quality.⁷
• Choose a tank with room to grow. Bigger volumes dilute waste and are easier to keep stable than small tanks.^{1, 7}

There isn’t one perfect litres-per-fish number that fits every setup, because filtration, planting, and maintenance matter. As a safety check, use welfare guidance that scales tank size to fish size (not shop size), then err larger if you can.^{1, 7}

Filtration and cycling: the quiet machinery that keeps fish alive

Goldfish are enthusiastic eaters and heavy waste producers. A tank can look clear and still be chemically unsafe, especially when ammonia or nitrite is present. In a cycled aquarium, ammonia and nitrite should be kept at zero, with nitrate managed through water changes and plant uptake.⁸

• Use a filter rated above your tank volume (goldfish systems often need “oversized” filtration because of waste load).
• Don’t replace all filter media at once. That’s where much of the beneficial bacteria live.
• Test water regularly (ammonia, nitrite, nitrate), especially after adding fish, changing feeding, or cleaning the filter.⁸

Water temperature and placement

Goldfish are generally considered cool-water fish. What matters most is stability: keep the tank out of direct sun and away from heat spikes, and avoid sudden temperature swings during water changes.

Decor, plants, and substrate

Goldfish explore with their mouths and can be rough on delicate plants. Choose décor that won’t tear fins or trap fish.

• Smooth hardscape (rounded stones, driftwood without sharp points).
• Hardy plants such as anubias and java fern (often better tied to wood or rock than planted in soft substrate).
• Substrate you can clean—detritus collects quickly in goldfish tanks, so pick gravel or sand you can vacuum effectively.

Feeding and nutrition

A goldfish diet works best when it’s steady and varied: a quality staple food, plus plant matter and occasional higher-protein items. Overfeeding is one of the fastest ways to foul water, so portion control matters as much as food choice.¹

• Staple: quality sinking pellets formulated for goldfish (often easier on water quality than flakes).
• Add fibre: blanched peas (skins removed), spinach, or other soft greens in small amounts.
• Occasional protein: frozen foods such as daphnia or brine shrimp.
• Avoid: bread and fatty human foods; they add waste without proper nutrition.

Feed only what they finish in a couple of minutes, then remove leftovers.

Health and lifespan

With space, clean water, and consistent care, goldfish can live for many years. Australian biosecurity guidance notes typical lifespans around 9–10 years, with some individuals living much longer under favourable conditions.⁴

Many common problems trace back to environment rather than “bad luck”: persistent ammonia or nitrite, high nitrate, poor oxygenation, and chronic overfeeding. Prioritising water testing and routine maintenance prevents more illness than most bottled cures ever will.⁸

Signs something is wrong

• Gasping at the surface or rapid gill movement
• Clamped fins, lingering at the bottom, or unusual hiding
• Flashing (rubbing on objects), ulcers, fuzzy growths, or white spots
• Sudden buoyancy changes (floating, sinking, rolling), especially in fancy varieties

If several fish are affected at once, test the water first—poor water quality is often the common denominator. For persistent or severe illness, seek help from a veterinarian experienced with fish.

Maintenance and cleaning

Goldfish tanks stay healthy through small, regular interventions rather than occasional deep cleans.

• Weekly: partial water change and substrate vacuum to remove waste.
• Regularly: test ammonia, nitrite, and nitrate; adjust water change volume/frequency if nitrate creeps up.⁸
• As needed: rinse filter sponges/media in old tank water (not under the tap) to preserve beneficial bacteria.

Seasonal heat is often the hardest stressor in Australian homes. In hot weather, watch for rising temperatures and reduced oxygen, and increase aeration if fish are breathing hard at the surface.

If you can’t keep your goldfish anymore

Rehoming is part of responsible fishkeeping. If rehoming isn’t possible and a fish is suffering with a poor prognosis, humane euthanasia may be the kindest option. RSPCA guidance describes an anaesthetic overdose as the most humane method available for sick or injured aquarium fish.⁹

Never dispose of live fish by flushing, releasing into a waterway, or “setting them free” in a local pond—this can spread pests and disease and is specifically warned against by Australian biosecurity authorities.^{1, 2, 4}

Fun facts (kept realistic)

The “three-second memory” story doesn’t hold up. Goldfish can learn routines and retain information for far longer than a few seconds, with research and expert commentary describing memory that can last weeks or months depending on the task and conditions.¹⁰

What looks like simple wandering is often systematic foraging: a goldfish moves through the tank in loops and pauses, sampling surfaces for edible particles and plant matter.

Final thoughts

A goldfish does best in a roomy, filtered system where the water stays steady and clean, and the feeding doesn’t outrun the biology. Once those foundations are in place, their colour, movement, and quietly persistent foraging become the easy part to enjoy.

References

1. Queensland Government – Prevent the spread of invasive freshwater animals
2. Queensland Government – Identifying invasive freshwater animals
3. Fishes of Australia – Goldfish (Carassius auratus) species profile
4. Business Queensland – Goldfish (biosecurity and impacts)
5. NSW DPI – Goldfish (freshwater pest profile)
6. Encyclopaedia Britannica – Goldfish
7. RSPCA Victoria – Fish care and aquarium setup (including bowls and tank sizing)
8. Merck Veterinary Manual – Water quality in aquariums
9. RSPCA Australia Knowledgebase – Humane euthanasia of aquarium fish
10. Live Science – Goldfish memory myth explained (expert commentary and research background)