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Shubunkins are similar to the common goldfish and comet goldfish in appearance. They were first bred in Japan, from mutations in telescope eye goldfish (Demekins) c. 1900. They have streamlined bodies with well-developed and even fins. However, the Shubunkins are calico goldfish; they possess nacreous scales (an intermediate between metallic and transparent scales that are pearly in appearance). The overlapping patches of red, white, blue, grey and black (along with dark speckles) normally extend to the finnage of Shubunkins. Blue is the most prized colour in Shubunkins. Calico originally denoted three coloured varieties of goldfish that did not include blue. The best blues are produced from line breeding of good blue specimens of Shubunkins. Sometimes good blues may be obtained by breeding bronze (metallic) with "pink" (matt-scaled) goldfish, but a grey slate colour may result instead.
It may take several months for the nacreous coloration to develop on a young fry (baby fish). Shubunkins are excellent pond fish because they reach a length of 9 to 18 inches (23 to 46 cm) at adulthood. A Shubunkin goldfish is considered an adult at 2 to 3 years of age, even though they live much longer.
Blue colouring in goldfish comes from black pigment within the body wall. It will not show as blue in fish with metallic type scales, but will look blue if the fish has matt or nacreous scales. The nacreous (formerly called calico) scale type is produced in a fish that carries the gene for metallic scales, as well as the gene for matt scales (the fish is heterozygous). Only nacreous scales are accepted by the Shubunkin breed standards.
- When two fish with nacreous scales breed together, the offspring will on average include 1/4 with metallic scales, 1/4 with matt scales, and 1/2 with nacreous scales.
- If a fish with nacreous scales breeds with a fish with metallic scales, the offspring will on average include 1/2 metallic and 1/2 nacreous.
- If a fish with nacreous scales breeds with a fish with matt scales, the offspring will on average include 1/2 matt and 1/2 nacreous.
- London Shubunkins have stout bodies and also short, rounded finnage that is similar to the common goldfish.
- American Shubunkins (pictured in infobox) have a slimmer body shape than the london Shubunkin with deeply forked, pointed tail fins, and longer finnage all around.
- Bristol Shubunkins are slim bodied goldfish with well-developed finnage possessing a tail that is large, moderately forked, and rounded at the end making a shape similar to that of the capitalized letter "B".
- Axelrod, H.R.; Vorderwinkler, W. (1984). Goldfish and koi in your home. T.F.H. Publications. ISBN 0-86622-041-0.
- Chris Andrews, Interpet Publishing (2002) An Interpet Guide to Fancy Goldfish. ISBN 1-902389-64-6
- Erik L. Johnson, D.V.M. and Richard E. Hess (2006) Fancy Goldfish: A Complete Guide to Care and Collecting, Weatherhill, Shambala Publications, Inc. ISBN 0-8348-0448-4