The goldfish has a fairly self explanatory name: "gold" describing its color, and "fish" describing its species. Goldfish are a relatively small member of the Cyprinidae or carp family. The Cyprinidae family is the largest family of freshwater fishes in the world. Apart from the goldfish, other well-known members include the minnow, chub, shiner, zebrafish, various Asian carps and koi.
Selective breeding over centuries has produced many different color variations, some of them far removed from the 'golden' color of the original goldfish. There are also different body shapes, fin and eye configurations. Some extreme versions of the goldfish need to be kept in indoor aquariums as they are much less hardy than varieties closer to the "natural" original. However, some varieties such as the Shubunkin are hardier, and can be kept in outdoor pools.
Goldfish may also change their color by varying the spectrum of light under which they are kept. Goldfish produce pigment in response to light. Cells called chromatophores produce pigments that reflect light, and gives coloration. The color of a goldfish is determined by which pigments are in the cells, how many pigments molecules there are, and whether the pigment is grouped inside the cell or is spaced throughout the cytoplasm. If a goldfish is kept in the dark it will appear lighter in the morning, and over a long period of time will lose its color.
Goldfish can grow to a maximum length of about 18 inches (48 cm) and a maximum weight of about 10 pounds (4.5 kg). However, this is rare, few goldfish reach even half this size. The longest goldfish measured was 47.4 cm (18.7 in) from snout to tail-fin end in Hapert, The Netherlands.[5] The longest fancy goldfish measured was an oranda called Bruce. It was measured at 40 cm (15.75 in) in Hong Kong, in 2002.[6][7]
In optimal conditions, goldfish may live more than 20 years, but most household goldfish generally live less than six to eight years, due to sub-optimal living conditions (such as being kept in bowls). The oldest recorded goldfish lived to 49 years.[8] The collective noun for a group of goldfish is a 'troubling' of goldfish.[9]
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