Japanese koi fish: A suitable candidate for backyard ornamental fish farming in Manipur

Dr. Chimwar Wanglar, Ms. Soniya Laishram,  Dr. Nilachandra Thangjam, Mr. Suraj Kumar Irungbam, Dr. Bedajit Yumnam, Dr. Dipak Nath, Dr.Angam Raleng, Prof. Ratan Kumar Saha and Prof. Phurailatpam Ranjit Sharma
Introduction: Nishikigoi/Japanese koi/Koi, a mutant variety of Cyprinus carpio (puklaobi) fish, is one of the most expensive and popular decorative fishes in the world. Koi are unique multicolor fish and multiple color varieties have been developed since the early 1800s in the Niigata province of Japan.
It is believed that koi varieties were descendents of Magoi (black carp) variety, which were cultured as food fish in China and transported to Japan around 1000 AD. In the early 1800s in Japan, colorful patterns and varieties of this fishes were observed and selectively bred for these characteristics which gained extreme popularity.
Koi were first introduced to the USA in early 1940s while koi were not seen in Great Britain until the 1960s. Since then koi keeping and breeding has gained worldwide following in Asia, Europe, South Africa, etc. Generally, Koi are 30 to 60 cm long and have a typical life span of around 40 years, though the oldest-known koi (Hanako) lived to be 226 years old.
In 2018, the most expensive koi was sold at about 1.8 million US dollars. It was a 3 foot koi name S legend kohaku variety. The value of each Koi fish is based on the specific color pattern, size, body conformation, intensity of the color, etc. However, most of the koi color types are not true breeds i.e. the patterns are not repeatable. Koi farming depends largely on strict and continuous culling throughout the culture period making it expensive to obtain a particular breed or line.
Although most koi around the world are Japanese origin, however, there are differences in quality between the domestic (other countries) and the Japanese breed. Japanese koi breeders have been producing koi for generations by rigorous culling to maintain a gene pool of high quality koi. Generally, it is believed that the highest quality Japanese koi is never exported to other countries. Koi breeders around the world focus more on faster growth and early breeding to generate mix varieties that are generally cheaper.
Domestic Koi Fish Japanese Koi Fish
Bred from mixed varieties of koi Japanese bred from ancient varieties of koi (generally breed and maintained for several generations) breed when the fishes attain as early as 1 year Breed generally when the fishes attain 4 years
Higher fecundity Lower fecundity
Faster growth rate Slower growth rate
Concentrate on the mix varieties Concentrate on few varieties to achieve high level quality breed/line
Smaller size ( 12-15 inches on average) Larger size ( up to 36 inches)
Sold generally at any size and age and not intended for auction Mainly for auction and to be sold at higher prices
Affordable for all enthusiasts Expensive
Shorter lifespan (15 years on average) Longer lifespan (commonly reaching 50-60 years)
Easier to keep in an aquarium Generally cultured in big ponds
Common varieties of Koi:
Currently as many as 120 different koi varieties are distinguished and the most popular category is the Gosanke (Kohaku, taisho sanshoku, showasanshoku), Tancho, Chagoi, Asagi, Bekko, Ogon, Kawarigoi, etc. Other new varieties such as Ghost koi, Butterfly/Hirenaga/longfin koi, though they are not considered true Nishikigoi. Some common varieties are discussed below.
Kohaku indicates “red and white” and these fishes have white background with red markings across the body.
Taisho sanshoku otherwise known as Sanke koi are similar to Kohaku but have additional black markings on their body.
Showa sanshoku or Showa are black koi with red and white markings on the body. Recently, the amount of Sanke has increased and can be difficult to distinguish from Showa.
Bekko are white, red or yellow background with black markings in the body.
Tancho is any koi with solitary red patch on its head.
Kawarigoi are koi that cannot be put into any one of the major categories.
Kohaku Sanke Showa Bekko Tancho Butterfly
Reproductive biology: The age of maturity for breeding of koi varies from 1 to 4 years for both the males and females.  They tend to mature earlier in tropical waters than northern parts of Europe and America. Once they mature, they tend to breed every year. Some breeders have managed to breed the kois twice per year, but the female koi will lay significantly fewer eggs in the second time around.
A matured female can release around 100,000 to 150,000 eggs per kg body weight of fish (domestic koi are found to spawn as many as 400,000 eggs per kg female).
However, only around 60% of these eggs will hatch and even fewer may have reasonable chances of becoming a fry. The best results are observed when the female is at least 4 years old and a male at least 3 years old. The reason being is that the female would be of a good size and in good condition which would let her carry many thousand large, quality eggs with a good yolk sac.
The larger the yolk sac the larger the fry and the quicker they will eat microscopic food so the faster they will grow. It is also an advantage to use a large koi of 4 years as they have better ability to cope with the many hours of the spawning cycle.
Breeding of Koi
Brooder selection : Koi females develop two large ovaries which take up major part of the body cavity. So, the first sign of readiness of koi females for spawning is the presence of a pronounced, round and soft abdomen. Males do not have enlarged abdomens and gentle pressure on the abdomen near the genital pore will release milt/sperm that is white in color. Both the male and female fishes have to be weighed to calculate the appropriate amount of hormones for injection.
Female Koi Fish Male Koi Fish
Body shape Shorter and rounder body Longer and slender body
Pectoral fins Rounder, almost translucent Pointy, opaque, intensely colored
Vent appearance (anus) Transverse slit running across the slightly protruding vent Rounder vent
Physical changesduring mating Will become rounder and chunkier. Will develop sandpaper-textured white tubercles on the side of their face and on their pectoral fins.
Breeding management : Breeding of koi fish can be done in both natural and artificial ways in confined waters like tanks and ponds. It is essential to provide some substrates which may be in the form of roots of water hyacinth, plastic straps, nylon filaments, etc., to help the sticky eggs to adhere and for easy collection of the eggs. The male and female brooder fishes are to be kept separately, at least two weeks, before breeding them and fed with protein rich formulated diets with some treats in the form of tubifex worms, mealworms, redworms, insect larvae, etc., for faster gonadal development.
Koi are omnivorous feeders and will eat food found at all depths of water. High carbohydrate feeds should be avoided to prevent deposition of fat. Avoid overcrowding and stress while netting. Spawning is triggered by factors like temperature, water parameters, pH, etc. Optimum temperature for breeding of koi is 18 to 22oC and pH of 7. Fluctuation in pH is not suitable for koi breeding.
The Dissolved Oxygen should not be less than 5ppm (mg/l). The ammonia level should not exceed 0.05ppm. It is not advisable to feed the koi while they are in the breeding tank. The tank should be filled with treated, fresh water of pH 7 to 7.5 and if possible the water temp should be 5o C below the main pond temperature.
This helps stimulate the females andmimics the natural habitat. Brooder fishes should not be kept in the breeding pond/tank for more than 4 days.
Natural breeding: Similar to common carp, Koi fish can breed naturally in tanks and ponds under optimal conditions.   (To be contd)