SPCA New Zealand
Advice & welfare

Caring for fish

While fish are amazing pets, they are also a serious commitment. Fish are living beings with needs, wants, and feelings - just like you and I. They require a lot of time, money, love, and understanding – they are not low maintenance pets. It is your responsibility to keep your fish safe, happy, and healthy.

Note: Each species and breed of fish have different, varying needs – the below information is a general guide. Be sure to consult a fish specialist/veterinarian regarding the specific health and welfare needs of your fish.


What, when, where, and how your fish eat really depends on their species. There are thousands of different species of fish, all with different dietary needs. Learning how your fish naturally eats is essential. Different species of fish have different styles of eating. Research if your fish is a top feeder, middle feeder, bottom feeder, or grazer.

It is essential to feed your fish the appropriate food for their species, as it will ensure that they get the right type of nutrients in the right amounts. Not only do fish need fish flakes/pellets as part of their diet, many species of fish also require a mix of other foods for balanced nutrition and enrichment. What someone would feed their goldfish compared to what someone would feed their tropical fish differs greatly. It is always best to talk to a veterinarian that specialises in caring for and treating fish, they can help you develop an appropriate meal plan for your fish.


When it comes to choosing the best aquarium for your fish – the bigger the better! A bowl, or any similarly small (i.e. less than 20L) enclosure, are NOT suitable environments for any fish. They are too small for your fish to show normal behaviour and it’s difficult to maintain good water quality.

A common myth about fish is that they will only grow to the size of their environment - this is simply not true. Fish will continue to grow, and a small environment is likely to cause many health issues. The tank must accommodate the fish when first purchased, to the point where they are fully grown. Some fish can become too large for an average home aquarium, e.g. pacu, giant gourami, red tailed catfish, shovel-nosed catfish, common pleco, arowana, and sturgeons, even the common goldfish can grow to 30 cm in length!

Tank size also needs to allow for suitable space for the number of fish you are wanting to look after. Many species of fish are social, schooling species and therefore need to be kept in a tank with multiple appropriate tank-mates.

A cover for your aquarium is vital as a lot of fish are keen jumpers. Covers also prevent objects from falling in the aquarium. Aquariums should be placed in a quiet environment, that does not experience significant changes in temperature and away from direct sunlight.

Provide your fish with lots of places to rest, hide and explore in their tank, such as, fake or real plants, driftwood, rocks, hide outs, shells, and hoops.

Enrichment idea: Creating a gradient/slope with the substrate (underlying layer) at the bottom of the tank is a great form of enrichment for your fish, as this is more interesting, complex, and natural than a flat bottom environment.

Water Quality

Maintaining good water quality (e.g. temperature, oxygen, pH, ammonia, nitrite levels, etc.) is extremely important to fish health and welfare. Water quality needs to be monitored daily in newly set up tanks and at least once a week in established tanks.

There are many at home testing kits available to use – always talk to a fish specialist to see which will work best for your fish and follow the instructions. Alternatively, check in with your local pet shop as some offer free water testing services.

All aquariums need a proper filter that is the right size in order to maintain good water quality. An aeration system, such as air stones, can also be added to ensure the water has enough oxygen. Filters provide a place for beneficial bacteria to grow. This is very important in the tank environment as the bacteria converts ammonia from fish waste, which is highly toxic to goldfish, to less harmful nitrates.


Even with a good quality filter and good bacteria, the water needs to be changed by 10-25% once a week to keep nitrate and nitrite at safe levels. When cleaning tanks, 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 chloramines that can harm fish. It’s important to match the temperature of the water to within two degrees of the water already in the tank.

You should regularly use a test kit to keep an eye on your aquarium’s ammonia or nitrite levels, you’ll need to change the water more often if you see spikes in these.


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. Fish have a harder time than other animals communicating when they are feeling ill – it is up to you as a responsible owner to do your research, carry-out daily health checks, and ensure they see a specialised fish vet if they ever show sign of illness or injury.


A fish that is behaving normally will be active (as is normal for that species), have rhythmic gill movements (a sign of good health) and will be motivated to feed. What constitutes as ‘normal’ and ‘abnormal’ behaviour will depend on the species, so it is important to know your species and get to know your individual fish.

Environmental enrichment and lots of space allows fish to express their natural behaviours. Always ensure anything you add to the aquarium is fish safe - any gravel, furniture, ornaments, and artificial plants should be smooth with no rough edges. Rough edges tear the delicate fins of the fish, which will affect their swimming. Additionally, all natural enrichment such as plants should be non-toxic for your fish.

Click here for more information on enrichment for fish

It is also important to consider the social environment of your fish. For fish that group together for social reasons (i.e. shoaling species), such as, neon tetras, white cloud mountain minnows, and zebrafish, it can be very distressing to be housed in a tank on their own. The number of fish you can keep in an aquarium depends not only on the size of your aquarium or pond, but also the behavioural needs of your fish. Keeping too many fish in the aquarium means they'll have to compete for food and/or resources like hideouts which may result in them becoming stressed. Moreover, some fish are simply just not compatible. For example, Siamese Fighting Fish are a breed of fish that will fight with other fish, so they prefer to be alone. If your fish are fighting, it is something that needs to be addressed immediately so that it does not get out of hand.

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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