Goldfish (Carassius auratus)

Synonyms: Cyprinus auratus, Carassius auratus auratus

Common Names: Golden carp, wild goldfish

Description:

Goldfish (Carassius auratus) is a fish in the minnow and carp family, native to eastern Asia, and one of the earliest foreign fish brought to North America [1][2]. The familiar orange pet often loses its bright color in the wild, growing into a large, drab, fast-breeding fish that muddies the water and crowds out native species [2]. MISIN tracks goldfish because released pets and pond fish have set up wild populations that are very hard to remove once established [2][3].

Identification:

Wild goldfish look very different from the bright pets people picture. They have a deep, stocky body and, in the wild, range in color from gold or brassy bronze to olive-green, gray, or creamy white [2]. A grown wild goldfish is usually 4 to 8 inches long but can reach well over a foot [2]. Two features help confirm it: goldfish have a long dorsal fin (the fin along the back) with a stout, saw-toothed spine at its front edge, and ? unlike the very similar common carp ? they have no barbels (the whisker-like feelers) at the corners of the mouth [2].

Goldfish are easiest to notice in late spring and early summer, when adults gather to spawn in shallow, weedy water near shore and can be seen splashing in the shallows [2]. Drab wild goldfish are easy to mistake for young carp, so check the mouth for the missing barbels [2].

At-a-glance cues:

1. Deep, stocky body; wild fish are often gold, bronze, olive, gray, or white rather than bright orange [2]
2. No barbels (whisker-like feelers) at the mouth ? common carp and koi have them [2]
3. Long dorsal fin with a stout, saw-toothed spine at its front edge [2]
4. Adults gather to spawn in shallow, weedy water in late spring and early summer [2]

Habitat:

Goldfish are native to eastern Asia and were brought to North America centuries ago as ornamental fish; they are now found in waters across much of the United States [1][2]. They live in quiet, shallow water ? the backwaters and pools of slow streams, along with ponds, lakes, ditches, and marshy edges ? especially where the bottom is mucky and plants are present [2].

Part of what makes goldfish such a successful invader is how tough they are. They tolerate muddy, low-oxygen, and polluted water better than most native fish, and they survive a wide range of temperatures, from near freezing to very warm water [2]. This lets them thrive in disturbed ponds and waters where native fish struggle [2].

Reproduction:

Goldfish reach new waters almost entirely because people put them there. The most common way is the release of unwanted pets and the dumping of aquarium or backyard-pond water into ponds, lakes, ditches, or storm drains; goldfish used as live bait and then released add to the problem [2]. Just a few released fish can start a population [2].

Once in the water, goldfish breed fast. They spawn in shallow, weedy areas in late spring and summer, and a single female can release up to several hundred thousand sticky eggs that cling to underwater plants, often spawning more than once in a season [2]. Goldfish can also breed with common carp to produce hybrids [2]. Because populations build so quickly and the fish are long-lived, the most important step is preventing release in the first place [2][3].

Impact and Damage:

For a homeowner, the clearest impact shows up in backyard and farm ponds. A few dumped pet goldfish can multiply into a crowd of large, drab fish that constantly stir up the bottom, turning the water cloudy and brown, killing off the pond plants, and feeding algae blooms [2]. Goldfish are not a danger to people or pets, but they can quickly ruin the look and health of a pond [2].

In natural waters the damage is broader. As goldfish root through the bottom for food, they raise the cloudiness (turbidity) of the water, which shades out and reduces underwater plants and can trigger algae blooms. They compete with native fish for food and also eat the eggs and young of native species, reducing their numbers [2]. Released goldfish can also spread fish diseases, such as koi herpesvirus, that cause die-offs in other fish [3]. Once established, goldfish populations are very difficult and costly to control [3].

Similar species:

Drab wild goldfish are easily mistaken for other carp-family fish.

Common carp (Cyprinus carpio) is the most common mix-up because both have deep bodies and a saw-toothed dorsal spine, but common carp have two pairs of barbels (whisker-like feelers) at the mouth, which goldfish completely lack [2].

Koi (Cyprinus carpio) are a colorful domestic form of common carp often kept in ponds and confused with goldfish, but like other common carp they have barbels at the mouth and usually grow much larger [2].

Crucian carp (Carassius carassius) is a close Eurasian relative that looks very similar and also lacks barbels, separated mainly by fine details such as scale and fin-ray counts that usually require close inspection [2].

Prussian carp (Carassius gibelio) is another closely related, barbel-less carp that is nearly identical to a wild goldfish and is reliably told apart only by counting scales and gill rakers or by genetic testing [2].

Monitoring and rapid response:

Signs to watch for:

1. Schools of deep-bodied gold, bronze, olive, or drab fish in ponds, ditches, or slow shallow water [2]
2. Fish splashing and gathering in shallow, weedy areas to spawn in late spring and early summer [2]
3. Pond or backwater water that has turned cloudy and brown, with aquatic plants disappearing

What you can do:

1. Never release pet goldfish or dump aquarium or pond water into any lake, stream, ditch, or storm drain ? this is the main way goldfish spread [2].
2. Rehome unwanted goldfish (give them to another hobbyist or return them to a pet store) instead of setting them free [2].
3. Never use goldfish as live bait or empty a bait bucket into the water [2].
4. In a small private backyard pond, you may be able to net out goldfish and keep the pond from draining into natural waterways; dispose of removed fish in the trash, not in another waterbody [2].
5. Coordinated removal across a larger pond or connected waters ? netting, draining, or stocking predators ? is usually an agency-led effort and most methods require permits [3].

When to call a professional:

1. Goldfish established in a lake, stream, or any water connected to other waterbodies, where they cannot be contained [2][3]
2. Any control method that involves draining, pond drawdown, or pesticide use, which typically requires permits and trained staff [3]
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. Integrated Taxonomic Information System (ITIS). Carassius auratus (Linnaeus, 1758). itis.gov
2. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Carassius auratus (goldfish) ? Species Profile. nas.er.usgs.gov
3. Minnesota Department of Natural Resources. Goldfish (Carassius auratus). dnr.state.mn.us

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