If you like to keep fish that are both interesting to look at and great to show off, you might like to consider Koi, which are a type of Asian ornamental carp fish.

Koi come in a range of bright colours and patterns; e.g. black with coloured triangles, or black with orange belly and points, or white with several colours, as well as a number of varieties and combinations. They can grow quite large, up to almost a metre in length.

Types of Koi include fully-scaled (considered to be the norm for this fish), line-scaled, mostly scale-devoid and warrior-scaled. There are 13 classes of Koi which fall into either the metallic or non-metallic varieties. The Koi are classed according to colour and pattern.

Caring for Koi fish

  • Diet: According to the Australian Koi Farm in NSW, Koi should never be fed animal fats or dairy products as they are unable to digest these. Koi require a balanced diet which contains a combination of macro and micro-nutrients, so the best food is the specialised Koi variety. There are various types of food available, e.g. for rapid growth, seasons (summer and winter), colour enhancer (for showing) and building immunity. However it might be simpler to just buy a general all-round Koi fish food, as the separate kinds can work out to be quite expensive.


  • Habitat: Koi fish should be kept in chlorine-free water with pH level above 7.2-7.5 (neutral). A filter is necessary in your pond to keep the water healthy. If you notice a change in the fish’s behaviour, you should check the water for the presence of ammonia. If it is found it will be necessary to change the water completely. Ammonia can also be an indicator of an overstocked pond, or an inadequate filter.
  • Diseases to look for include:

– Fulminant Gill Rot, symptoms of which are 50% or more of the gills being eaten away. At this stage there is no effective treatment.
– Aeromonas Hydrophilla is a disease which results in erosions of the fins, snout and tail. Treatments such as antibiotics may help. This disease can be largely prevented by good husbandry practices.
– Aeromonas Salmonicida results in ulcers on the body. This disease may be treated with antibacterials. Immuno-stimulants for fish may act as a preventative measure.

Pond types include those made from bricks, concrete and fibreglass, amongst others. The Koi Farm recommends fibreglass ponds, or at least fibreglass sealing of the other types. Problems with ponds can include the location, inadequate filtration and poor construction, so it is important to carefully consider all of these elements when installing your pond.

Koi are vulnerable to predators such as large birds and cats, especially with their bright colours, so if you are installing an outdoor pond, it should be built in a shaded area and may require netting of some sort over the top to help protect the fish. A UV clarifier is also a useful addition to detoxify the water from fungi and viruses and helps keep your fish healthy.

Breeding Koi is quite a complex procedure which involves removing the breeding fish to a separate location with the right conditions, keeping the eggs at a specific temperature and feeding with a special diet. It’s probably easier to leave it to the professionals!

Buying Koi is a long-term commitment as these fish may live up to 35 years or even longer in some cases. It is important to educate yourself with as much information as possible prior to collecting your new pets.