Ornamental Fish Production and Management (1+1)

11.2.2 Koi-carp

The name koi in Japanese means carp but these are usually taken to be the colourful derivatives of Cyprinus carpio, alternatively called nishikigoi (coloured cloth in Japanese). Developed in Japan from black ancestors originating in China, the coloured varieties date from the 16^th century. The major colour and scale variations popular today have been generated in the last 50 years and are still being added to. Koi enjoy world-wide reputation and command extraordinary high prices. Like goldfish, they can live for many years and represent valuable ‘investments’.

They are classified according to a Japanese system devised for show purposes and the names frequently reflect aspects of the varieties, history or place of origin. Simple patches of one colour superimposed on the background of another is the basis of most of the traditional varieties. Thus Kohaku are white fish with red patches, Taisho sanke white, whilst Showa sanshoku contain much more black, to the extent that it can be regarded as a black fish with added kohaku, a white fish with a solitary red patch on top of the head in the most valued specimens this is round like the rising sun symbol on the national flag of Japan. All of these varieties and the non-valued all-white specimens are said to be found amongst offspring of any cross within these varieties.

Further varieties include black on white (Bekko) and its obverse (utsuri) together with Shusui in which linear scale patterns are combined with other characteristics. These scale patterns are closely akin to the scaly and line characteristics of common carp.

Colour patterns are not so simply inherited but may also be due to the varied segregation of a few simply Mendelian alleles. There is also a common theme in fish genetics of duplicated loci where this can lead to tetrasomic inheritance. i.e. four genes segregating and not tow and so greater complexity arises.

Other body colours of orange and yellow are also found, and a blue type probably relates to dilution of the normal black pigment. Scale pigmentation variation characterizes some varieties, and others show the metallic sheer probably produced by excessive deposition of guanine in the scales.

The history of varied colour patterns is not well documented but seems to follow a pattern of inbreeding with the chance occurrence of distinctive mutations. The overall gold form is stated to be the consequence of recessive allele at two loci which the metallic sheer is due to one single recessive allele. All three in combination produce the white fish. In addition to this it seems likely that scale transparency follows the model observed earlier with common carp and is determined by a recessive or partially dominant gene. The reticulation pattern of melanphores on scales resembles ‘gold’ in the guppy and that was controlled by a simple recessive allele. Thus more than seven loci seem to be involved, with differing degrees of dominance. The genetic situation with respect to koi varieties is thus very complex: strains breed true to some basic features but give rise also to much further variation, and the prospects for developing yet more forms seen excellent, particularly if different strains are crossed.

Most of the world’s finest koi now come from Japan but a growing interest in selective breeding of these fish is taking place in many countries. New developments include the introduction of fin shape into the koi gene pool, and body shape may come next. Chromosome engineering would also be usefully developed in koi culture if only as a means of protecting valuable genetic stock by providing for sale only sterile triploids. Thus the selective breeding of koi has some potential.