Photo credit: U.S. Geological Survey, Bugwood.org
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Species at a Glance
The goldfish, which is a member of the minnow family, was one of the first aquatic invasive species to reach North America, arriving in the 1600s as ornamental fish for aquariums and water gardens. It is now one of the world’s most widespread invasive species.
The elongated, stout body is typically 10-20 cm (4-8 in) in length and weighs 0.03 kg (0.06 lbs), although it can reach a maximum length of 59 cm (23 in) and maximum weight of 3 kg (7 lbs). It has a long dorsal fin with 15-24 rays and a hard serrate spine at the origin of both the dorsal and anal fins. There are normally 26-32 scales in the lateral line. The mouth is small, terminal, and lacks barbels. While the goldfish was mostly golden in color one thousand years ago, it now comes in a variety of colors, including orange, yellow, white, black, silver, olive-green or greenish-brown and combinations of these colors. When found in nature, the goldfish is most often a shade of green, brown, or gray.
The goldfish may be confused with the common carp (Cyprinus carpio), which has two pairs of barbels on the upper jaw, a non-serrate spine, and typically more than 32 scales in the lateral line. However, goldfish can hybridize with the common carp, producing individuals with both characteristics.
While preferring a habitat with a muddy bottom and thick vegetation, the goldfish can tolerate pollution, temperature fluctuations, and high levels of turbidity. It lives in freshwater ponds and slow-moving or still waters in depths of up to 19.8 m (65 ft) and prefers temperatures of 4-41°C (40-106°F); although it cannot live for long at high temperatures.
Intentionally introduced to ponds, fountains, and small lakes for ornamental purposes, the goldfish was able to escape and disperse through connecting waters. Many introductions of goldfish were also due to its use as live bait. In addition, the goldfish is often released into the wild by pet owners not realizing the environmental repercussions of setting the fish free.
Native to eastern Asia, the goldfish has been reported invasive in the United States by every state except for Alaska, and is established in all of the Mid-Atlantic states.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
The goldfish is believed to be responsible for population declines in many native fish, invertebrate, and plant species. It also uproots plants and creates enormous turbidity due to its aggressive bottom feeding behavior.
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).