Caring for your pet fish

GoldfishGoldfish are one of the most common fish species kept as pets. They are colourful, peaceful, and have a long lifespan. Depending on breed, goldfish can grow to 10 to 20cm.

Fish can make good pets but buying a fish should be a long term decision as they can live for up to 20 years. Fish need regular maintenance to ensure they kept healthy and their environment is clean.

If you no longer want to keep your fish you need to find an alternative home or humanely kill the fish.

Do not release live goldfish (or other non-native fish) into dams, rivers or other waterways (or down the toilet) as they can carry diseases that can affect our native species. They can also establish populations in waterways that compete with our native populations.

If you are unsure about how to care for your fish speak with your vet or a person experienced in the care of fish.


The welfare of all animals, including fish is protected by the Prevention of Cruelty to Animals Act 1986.

Choosing a fish

When selecting fish they should:

  • be clear and bright, fins held erect
  • be alert and swim without undue effort
  • not be sinking or bobbing to the surface
  • not have lumps, bumps, wounds or clamped fins
  • not have a trail of excreta from their vent
  • not be 'sulking' in the corner.

If you have any doubt then do not select them.

Environment for your fish

Fish need a large aquarium that provides sufficient area for the species and number of fish being kept. Fish should have ample room to swim around. Where there are more fish in the aquarium more space is needed. A rough guide for space is at least 10 litres of water for each fish  up to 3cm long. Increase the amount of water as fish size increases.

Set up the aquarium with:

  • an aerator
  • filters
  • pondweed
  • plants
  • smooth pebbles (up to 7cm)
  • a rock or other item for hiding beneath.

You should attempt to replicate a natural environment for your fish.

All water environments should be stabilised before fish are added. Tap water should be conditioned by allowing it to stand for 2 to 7 days before adding plants and fish to allow the chlorine to evaporate. Use commercial preparations to keep the pH level between 6.5 and 8.0.

Saltwater tanks require experience and expert knowledge as they are more difficult to set up and maintain. If you are setting up a saltwater tank for the first time, get an experienced person to help you and do your research properly.

When an indoor aquarium is used, the water should be kept at room temperature and should not be exposed to direct sunlight as this will increase the growth of algae. Temperature range should be between 20 to 25°C.

Tropical aquariums need heated controlled temperature ranges depending on the species — check with the aquarium outlet or your local vet for specific requirements.

Filtration is essential for providing the correct environment for the health of the fish. Mechanical filtration systems are the easiest to use.

Lighting for your fish

No artificial lighting is usually required unless there are plants or the tank is set up for tropical fish. If you use lights, they must be set up with a timer. Lights should not be switched on and off often as this can upset the fish. Plants require light for up to 12 hours so set your timers to provide this.

Covering the aquarium

A glass or mesh covering over the aquarium should be provided:

  • if the fish are at risk of young children or other pets (such as cats) reaching into the aquarium
  • where the water is closer than 10cm to the top of the aquarium (so fish could jump out).

Only use a solid cover over the tank if a filter is in place and working. A solid cover helps stop dust and toxins from entering the aquarium.

Do not spray chemicals or cleaning products near the aquarium. These can kill your fish.

Always remember water safety around young children and ensure the tank is located so it is not a drowning hazard.

Shelter and refuge

The aquarium should have an area of refuge for your fish from lights, action and other fish. This can be created with plants and rocky overhangs.

Cleaning the aquarium

It is recommended that conditioned water (left to stand for 2 to 7 days to allow chlorine to evaporate) of the same temperature be used to replace approximately 25% of the water each week.

Cleaning of the aquarium should occur every term. To clean the aquarium:

  1. Remove the fish and place them in a covered container with 25% of their tank water and 75% fresh.
  2. Clean the sides of the glass, gravel and furniture items with fresh water.
  3. Do not use chemicals.
  4. Rinse the tank carefully and fill it again with conditioned water.
  5. Refill the tank and let it stand for half a day before returning the fish.

Feeding your fish

Manufactured fish foods (flakes and granules) can be fed to tropical or temperate fish. Only feed food quantities that can be eaten within a few minutes otherwise overfeeding and soiling of the water can occur.

Be careful not to overfeed fish. Ask your vet how much food your fish needs and how regularly it should be fed.

Supplementary feeding

Some fish  need frozen food mixtures, shrimp and larvae. Do not feed your fish these foods unless you are directed to by reputable source — your vet or aquarium outlet.

Health problems

Water quality is vital for ensuring healthy fish. Always keep aquarium clean with fresh water.

Indicators that your fish is sick include:

  • loss of appetite
  • listing
  • skin lesions
  • floating upside down
  • poor swimming balance
  • spots, ulcers or growths
  • failure to thrive.

Get advice from your local vet about any health issues that develop.

If a new fish seems unhealthy, keep it separate until you are sure it is fit and healthy. Adding the new fish straight to the aquarium can infect other fish.

Handling of fish

Fish with red markingsFish should not be handled or kept out of the water. It damages their skin and increases the risk of bacterial or fungal infections. An aquarium net should be used for capturing or moving fish. Fish should be transported in watertight clear plastic bags — half water and half air. Transport fish quickly. Do not leave them unattended or let the fish to heat.

Page last updated: 04 Jun 2020