Photographer: U.S. Fish and Wildlife Service Source: Bugwood.org Copyright: CC BY-NC 3.0 US
Wild goldfish become much larger animals than the domesticated goldfish commonly found in homes across the world, normally ranging from 5-10 inches but some have grown to 24 inches! Sometimes the wild populations maintain their “fancy” orange coloration, but they can vary from olive green to creamy silver. The dorsal fin has 15-21 rays, and a stiff serrated spine where the dorsal and anal fins meet. The anal fin of the male is concave, and the female’s anal fin is convex. The tail has a deep fork.
Overall, it is not yet considered a “pest species” but this fish has the potential to produce large populations and transmit several parasites and bacteria species to native populations. With them reaching larger body sizes in the wild, they start competing with native species. Their presence can increase water turbidity and reduce aquatic vegetation, changing ecosystem structure. Researchers have observed several native species become less successful after the establishment of wild goldfish populations. Also, they can introduce copepod parasites to native fish, such as Lernaea species. This parasitic copepod genus has been documented to also damage tadpoles from the frog genus Rana. Furthermore, wild goldfishes can carry several other types of parasites, myxozoan bacteria species, and koi herpesvirus, all of which can harm native fish populations.
They are adaptable and can withstand high levels of turbidity, temperature fluctuations, wide pH tolerance, and low dissolved oxygen levels. They are also more tolerant of water pollution than native North American fishes. Their diet selection is wide including small crustaceans, zooplankton, phytoplankton, insect larvae, fish fry and eggs, ground-floor vegetation and detritus. Females lay about 25 eggs, and five days after they hatch. The freshly hatched fish fry can take a couple of days to be fully agile when swimming. Life span is typically 7 years, but they can live up to 30 years.
This fish is one of the perfect examples of human interference allowing a pest to greatly expand its distribution. Being one of the earliest fish domesticated, it was imported to the United States as early as the 17th century, and intentionally dumped into the waters by settlers that wanted to add to the North American fish fauna. Over the next centuries, some state organizations were intentionally distributing this fish into other states as Fish Exchange Programs. In the early 1950s it was found in Texas. It is now present is several systems including the San Antonio, Guadalupe, San Jacinto, Buffalo Bayou near Houston, Tawakoni Reservoir, Conroe, and Nueces drainages.
Eastern Asia and Japan
U.S. Habitat: Any freshwater system, especially those with submerged aquatic vegetation.
U.S. Present: All states except Alaska, and also established in Puerto Rico.
For a point map distribution map provided by the U.S. Geological Survey click here.
After a few generations in the wild, the goldfish start to strongly resemble the Crucian carp (Carassius carassius). Some researchers think that some wild goldfish populations in the United States are a hybrid of the Crucian carp and goldfish: Carassius carassius auritus. It has also been observed to create hybrid populations with the common carp Cyprinus carpio.
The state of Texas does not have any restrictions on the collection of wild goldfish populations. Any that are caught should be eaten or destroyed. Spread awareness to friends and family about the impact of dumping pet fishes into local water habitats.
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