SPCA New Zealand
Advice & welfare

Caring for goldfish

Goldfish (Carassius auratus) are an intelligent and friendly breed of ornamental fish. Their natural habitat are the cool streams, lakes and ponds throughout Asia. Goldfish have an average lifespan of 10-15 years, with some species living up to 30 years!


Goldfish are omnivores, that is they eat both plant and animal material. Therefore, a varied diet will maximise the health of your goldfish. This can include a mixture of specialised goldfish flakes, pellets and dead brine shrimp.

Feed your goldfish 2-3 times a day. It is important not to overfeed your goldfish. Uneaten food will contaminate the tank and effect the water quality. Fish should be fed as much food as they eat in under 2 minutes. If food is left over after 2 minutes, remove the remainder of the food from the tank.

We recommend finding a veterinarian comfortable and experienced in treating fish for routine checkups on fish health and further information on caring for your fishy friends.


The type of goldfish you bring into your home will make a big difference in the size of tank you will need. Slim-bodied goldfish like Commons, Comets and Shubunkins may start out small as juveniles but can grow to be about 30cm long and therefore would need to be kept in a pond. If you don’t have the space for a pond, a fancy goldfish is probably a better fit for you. Fantails are one of the most common fancy goldfish, which make a great beginner fish. We recommend avoiding purchasing goldfish that have been selectively bred for traits e.g. bubble eye goldfish, as these traits can impair their health and welfare (you can read more about this here).


The bigger the tank the healthier and happier the fish. Fish need enough space to exercise and express their natural behaviours. Goldfish should never be kept in a bowl or any small, empty environment.

A good rule of thumb for tank volume is 75L for a fancy goldfish, plus 40L for each additional goldfish. Length should be a minimum of 4 x the adult body length, width a minimum 2 x the adult body length and height a minimum of 3 x the adult body length.

However, water quality is equally if not more important than tank size. Aquarium maintenance, filter capacity and water change schedule all play an equally important role. A greater volume of water will help in diluting toxins from fish waste between water changes.

Place your aquarium in a stable and quiet environment, one that doesn’t experience significant changes in temperature and away from direct sunlight. Sudden loud noises and vibrations can be stressful for fish, so please be considerate when moving passed the tank or lifting the tank lid.


Large goldfish breeds such as the common, comet and shubunkin are best suited in outdoor ponds, as they will require a large amount of space when they reach adult size.

As a general rule of thumb, ponds should be 60cm deep. It is good to provide a range of depths in the pond, so your fish can have a choice e.g. deeper sections with cooler water. The minimum depth of available water in the pond must be 30cm.

As with aquarium fish, the number of goldfish that can inhabit the pond will depend on the size of the available swimming space.

Aquatic plants must be placed in the pond to provide shelter and enrichment. Aquatic plants also help to maintain good water quality, as they remove nitrates and phosphates from the water and provide oxygen. However, during the night plants will absorb oxygen and produce CO2. Water quality, including oxygen levels, need to be maintained using a filter system, pond pumps and air stones or fountains.

You must provide protection for your fish from potential predators, such as birds and cats. Netting and fencing can assist in deterring predators. Aquatic plant cover and ripples caused by the filter system may also help as a visual barrier. Provide lots of hiding places, e.g. tunnels, rocks and plants, so your fish can seek shelter and feel safe.

Water Quality and Maintenance

Maintaining good water quality is one of the most important aspects to keeping your fish happy and healthy. Water quality needs to be monitored daily in newly set up tanks and at least once a week in established tanks. You can buy at home water testing kits or some pet shops offer free water testing survives.

Water quality parameters to keep an eye on:

  • Ammonia: <0.1ppm
  • Nitrite: <0.1ppm
  • Nitrate: <50ppm (<110ppm tolerance)
  • PH: 6.5-7.5 (tolerance range: 5.0-9.0)
  • KH: 70-140ppm
  • GH: 150ppm
  • Temperature: 20-24°C (tolerance range: 8-30°C)

It’s important to maintain a stable water temperature, using a water heater if necessary.

Filtration and Aeration

Goldfish eat a lot and produce a lot of waste. Therefore, an efficient filter of a suitable size is an absolute must in a goldfish tank. An aeration system, such as air stones, can also be added to ensure the water is well oxygenated.

Filters provide a place for beneficial bacteria to grow. Beneficial bacteria is very important in the tank environment as it converts ammonia from fish waste, which is highly toxic to goldfish, to less harmful nitrates. This process is known as the ‘nitrogen cycle’. In newly established aquariums there are not enough beneficial bacteria to eliminate all the toxins immediately and therefore extra care needs to be taken to ensure fish are healthy for the first 2-6 weeks, before the nitrogen cycle is established in your tank.

Even with a good quality filter and established beneficial bacteria, you will need to perform partial water changes of approximately 10-25% once a week, to maintain nitrate and nitrite at safe levels. When cleaning your tank, be careful not to remove all the beneficial bacteria, especially from the tank filter. The trick is to clean little and often.

All tap water needs to be treated with water conditioner (available at pet stores), before adding it into the tank. Tap water contains chlorine and chloromines that can harm your fish. Also, try your best to match the temperature of the water to within 2 degrees of the water already in the tank.

Although a necessary process, keep in mind that cleaning/water changes can be a stressful event for your fish. One way you can help reduce stress is by carrying out cleaning routinely and predictably, i.e. doing water changes at the same time every week, using the same method. That way your fish will either get used to the cleaning process or learn to adapt to it.


A huge part of keeping your fish healthy is a clean environment and healthy diet. A lot of the time when fish are sick, it’s because of a poorly kept aquarium and/or an improper diet. Varying levels of chemicals, lack of oxygen, inappropriate temperatures, etc. will all make your fish sick. Water filtration and a cleaning schedule are vital for the health of your fish.

We also recommend that you learn as much about your species of fish as possible. Knowing what your fish needs and how they usually behave will help you to provide them with the best possible life. Healthy goldfish should be able to swim actively with no floating or sinking issues (i.e. buoyancy issues) or lean to the side for prolonged periods of time. Their skin and fins should show no blemishes or signs of damage. Common goldfish conditions include buoyancy disorders, bacterial infections, parasites and ingesting items, which they shouldn’t.

Daily health-checks should be performed. Please consult your fish veterinarian if you notice any changes to your goldfish’s behaviour, body condition, appetite or general appearance, as it could be an indication of illness.


Providing environmental enrichment and lots of space in their tank allows goldfish to express their natural behaviours. Goldfish need furniture in their tank to keep them occupied and provide them with places to rest and hide. Provide your Goldfish with sand substrate and lots of plant cover (approximately 50% of the tank). Driftwood, decorations and bubble walls are also good additions, but make sure the materials are fish safe.

Goldfish are social animals and therefore need other friends in their tank. They are generally not aggressive and therefore can be housed with other goldfish and most community fish, provided that the fish are larger than the size of the goldfish’s mouth. It’s best to keep goldfish with tank mates that have similar swimming abilities, so they are not in competition for food or space.

Click here for more information on the importance of environmental enrichment for your fish.

Goldfish are very intelligent animals. They can be trained to do tricks and will recognise their guardians over time!

Additional Information

Visit the SPCA Kids’ Education Portal (www.spca.nz/kids) for more information on caring for your companion fish, including enrichment tips and helpful videos!

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