White perch (Morone americana)

Synonyms: Perca americana, Roccus americanus

Common Names: Silver perch, sea perch, gray perch, narrow-mouthed bass, bluenose perch, humpy

Description:

White perch (Morone americana) is a small silvery fish in the temperate bass family (Moronidae), native to the Atlantic coastal estuaries and rivers of eastern North America [1][2]. It invaded the Great Lakes in the 1950s by swimming through shipping canals, and it has since spread through ballast water, contaminated bait, and fish stocking [1]. MISIN tracks it because it preys on the eggs and young of native and game fish, competes with native fish, and hybridizes with the native white bass [1].

Identification:

White perch is a small, deep-bodied, silvery fish, usually about 7 to 12 inches long [1]. Its back is grayish-green to dark green-brown, its sides are silver, and its belly is silvery white; the body is deep and flattened side-to-side, and its two back (dorsal) fins are joined [1]. The single most useful field mark is what it lacks: white perch has no dark horizontal stripes on its sides, unlike the native white bass, which has several distinct dark lines running along its body [1].

Because it lives underwater, you are most likely to notice it when it is caught or netted ? anglers on Great Lakes waters and connected inland lakes are the usual finders. A silvery, deep-bodied fish with no side stripes and joined dorsal fins is the thing to check.

At-a-glance cues:

1. A small (about 7 to 12 inch), deep-bodied, silvery fish [1]
2. Grayish-green back, silver sides, silvery-white belly [1]
3. No dark horizontal stripes on the sides ? unlike the native white bass [1]
4. Two back (dorsal) fins that are joined together [1]

Habitat:

White perch is native to the Atlantic coastal region of eastern North America, where it lives in brackish estuaries, bays, and coastal rivers, and it adapts easily to fresh water [1]. It is not native to the Great Lakes basin [1].

Where it has invaded, it lives in the open lakes, bays, harbors, river mouths, and nearshore areas, and it moves into connected inland lakes [1]. It tolerates a wide range of conditions, which helps it establish and become abundant [1].

Reproduction:

White perch spreads between waters mostly with human help, so an angler or boater is the most likely way it reaches a new lake. It rides along in bait buckets and in the water in livewells and bilges, in ship ballast water, and through accidental or illegal stocking, and it swims on its own through connecting canals and channels [1]. The first Minnesota record, for example, was in Duluth Harbor in 1986 [1].

Once in a lake it breeds prolifically. It spawns in spring, and a single female releases roughly 20,000 to 150,000 sticky eggs that settle onto the bottom and hatch within about one to six days [1]. That high output lets a new population build quickly. Because there is no practical way to remove an established fish, the key is to keep it from arriving: never move fish or dump bait between waters.

Impact and Damage:

White perch is not a hazard to people ? it is a fish that is caught and eaten. Its harm is to native fish and lake food webs.

It feeds heavily on the eggs and young of other fish, including important native and game species, and competes with native fish for food and habitat, so it can drive down native fish populations [1]. It also eats large amounts of the tiny animals (zooplankton) that graze algae, and removing those grazers can help trigger algae blooms [1]. And it hybridizes with the native white bass (Morone chrysops), mixing into and diluting that native species [1]. Because it tolerates so much and breeds so fast, it can become one of the most abundant fish in a lake, crowding the fish community [1]. There is no effective way to control an established population, which is why keeping it out matters so much [1].

Similar species:

White perch is confused with a few other silvery panfish and bass, and telling it from the native white bass matters most because the two hybridize [1].

White bass (Morone chrysops) is the native fish most like it, and the one it interbreeds with ? but white bass has several distinct dark horizontal stripes running along its silvery sides and its two dorsal fins are separate, while white perch has no side stripes and joined dorsal fins [1].

Yellow perch (Perca flavescens) is a native fish that shares the "perch" name, but it is yellow-green with bold dark vertical bars down its sides and orange-tinted lower fins, quite unlike the plain silvery, stripeless white perch [1].

Striped bass (Morone saxatilis) is a much larger relative in the same family, easily separated by its long, streamlined body and the bold, unbroken dark horizontal stripes along its sides that white perch never has [1].

Monitoring and rapid response:

Signs to watch for:

1. A small, deep-bodied, silvery fish with no dark side stripes and joined dorsal fins, caught in Great Lakes waters or a connected inland lake [1]
2. New catches of such fish in a lake where they were not seen before [1]

What you can do:

1. The most important step is prevention: never move fish from one water to another, and never dump a bait bucket or release unused bait into any lake or stream ? dispose of unwanted bait in the trash [1].
2. Clean, drain, and dry your boat and gear between waters ? remove plants and mud, drain the livewell, bilge, and bait containers on land, and let everything dry before entering another waterbody [1].
3. If you think you have caught a white perch somewhere new, take clear photos, note the exact location, and report it ? do not release it into a different water.
4. For lake associations and stewards: promote Clean-Drain-Dry and bait-disposal messaging at boat launches and support agency monitoring of new waters, since there is no practical way to remove an established population [1].

When to call a professional:

1. Any suspected new occurrence ? report it to your state natural-resources agency and MISIN so biologists can confirm and monitor it [1]
2. Any silvery bass or perch you cannot confidently identify ? a photo-backed report is worth more than a guess, especially given the look-alike native white bass
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. Minnesota Department of Natural Resources. White perch (Morone americana). dnr.state.mn.us
2. Global Biodiversity Information Facility. Morone americana (Gmelin, 1789). gbif.org

---