Care

A domesticated version of the wild carp, Koi or Nishikigoi (which translates from Japanese as 'brocaded carp') were bred from food fish introduced from China. Their story mirrors that of goldfish and unusually coloured individuals are mentioned in records dating back around 1,300 years ago. Around 200 years ago, more focused selective breeding began and gradually gave rise to the varieties that are known today. Like pedigree dogs, koi colours are named and recognised but the outcome of their breeding is far less predictable, meaning that very few of the offspring make the grade. Of course, these differences are only skin deep, and this leads to the extreme variations in the value of these fishes - an expensive high-grade fish may well literally be one in a million. As they can be produced in greater quantity, lower grade fish are a good deal cheaper to buy but outside of the realms of showing, beauty is in the eye of the beholder! Whatever their grade, koi share the typical carp traits that make them one of the best of all pet fish, soon learning to associate their keeper with food and happily feeding from the hand. Some varieties are known to be more friendly than others and these often more modestly coloured fish can help make their companions more confident.

Koi are big fish and need big ponds. To ensure healthy development and maximise water volume, a pond designed for koi should be at least 1.2m/4' deep but the bigger the better. These are pets that get better with age and tend to outgrow smaller facilities, this leads to serious owners often upgrading their ponds as their fishes mature. Large, greedy carp in big ponds need serious filtration and this is a factor to be considered at the planning stage, with helpful hardware such as bottom drains installed in the early stages of construction. The fact that many standard garden ponds have one or two koi swimming amongst goldfish and orfe is a tribute to how hardy they are, and they'll enjoy uprooting the plants and foraging in the mud in the same way their wild ancestors did. The fact that dedicated koi ponds tend to be bare is testament to the fact that they demolish most attempts at planting, so ensure any vegetation is out of reach and consider adding a "plant filter" where the benefit of waste removal can be harnessed safe from the fishes. Unlike wildlife ponds, carp ponds are best filled using tap water to ensure healthy mineral content - keepers in soft water areas are advised to add buffers to increase KH levels and monitor these alongside the usual parameters such as ammonia and nitrite. As these conditions favour the growth of algae, an ultraviolet clarifier is usually an essential piece of equipment to maintain the clear water that allows you to appreciate your colourful pets.

Koi tend to be labelled in a number of ways, including country of origin (expect to pay more for Japanese fish), grade and occasionally variety names such as Ogon, Kohaku, Sanke, Showa, Utsuri, Shusui, Chagoi etc. Long-finned fish are generally known as Butterfly koi.

Recent studies have shown that the origins of domesticated koi and their genetics point to them being descended from the Eastern Amur carp C. rubrofuscus and not C. carpio. 

Feeding

Good quality specialised diets are available for all sizes of these fish including pellets and sticks. Take care to avoid the temptation of overfeeding - adding food little and often will soon train the fish to associate their owner with food. Feeding is linked to temperature and it's important to offer a cold weather formulation in late autumn, winter and early spring. Prawns, earthworms, lettuce and even orange segments are all good treats to be fed now and again. 

Breeding

Spawnings will occur naturally in the pond if sexually mature males and females are present, where conditions are to their liking (water quality, water temperature, light levels etc), and where there is a medium such as mops/ropes/brushes where the eggs can be scattered. However, many spawnings go unnoticed as the eggs are often consumed quickly by the parents and other fish in the pond. To ensure survival of the eggs/fry, the aquarist will usually have to intervene, collecting the eggs before they are devoured, and keeping them in a spacious container with pond plants and some continuous form of gentle oxygenation. The eggs typically hatch within 4-5 days, and the fry will feed on their yolk sacs for the first few days, after which time a constant supply of small live foods such as infusoria and daphnia will be required. Koi, of course, can be selectively bred in separate breeding ponds if the aquarist is fortunate to have access to this type of set-up. In this scenario, the water of the breeding pond should match that of the main pond, and it should be lined with spawning ropes and the like. A well-conditioned selected pair can then be added and observed regularly for signs of spawning. Once the eggs have been deposited over the spawning medium, these can be separated from the parents and grown on in an independent container as described above. Fry from home spawnings usually provide a great example of the work needed to produce quality fish, as typically the fish most likely to thrive are the ones closest to their wild carp ancestors.