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Largemouth Bass

Micropterus salmoides

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Largemouth Bass.

Learn about Largemouth Bass, including their identifying features, location, habitat and impacts.

Largemouth Bass (Micropterus salmoides) are freshwater fish and members of the sunfish family. They are a popular sport fish but can be invasive when introduced to new lakes and rivers. They are a top predators that primarily eat fish, but also feeds on insects, crustaceans and frogs.

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Identifying features

You can identify Largemouth Bass by their:

  • large, sloping mouth that extends past the eye
  • large, wide lower jaw slightly longer than the upper jaw
  • eye, which is often gold in colour
  • laterally compressed body (less than the Smallmouth Bass)
  • sides with irregular bars that form a stripe (very apparent in juveniles)
  • amber and clear pectoral fins
  • joined dorsal fins, that appear as 2 (with the separation between the 2 more obvious than in Smallmouth Bass)

The body colour of Largemouth Bass changes with size, condition and habitat. They will be darker with more contrasting markings in clear, weedy water. In cloudy water, they are a paler green colour overall.

Where is the species invasive?

Their recent spread is a result of accidental introductions from live bait and unauthorized transfers between waterbodies for recreational fishing.

In Canada, Largemouth Bass have been found invasive in:

  • southern British Columbia, including:
    • Columbia River system, including Vaseaux, Osoyoos, Kootenay and Christina lakes
    • Lower Fraser River Watershed
    • South Thompson River Watershed
  • Ontario
    • some populations in western Ontario on the borders to the States and Manitoba
  • Quebec
    • Saint Lawrence River
    • Richelieu-Lake Champlain system
  • Saskatchewan
    • Boundary Reservoir on the Souris River
  • New Brunswick
    • St. Croix River
    • Saint John River (Meduxnekeag and Mactaquac Arm)

The Largemouth Bass is currently not reported in Nova Scotia, Prince Edward Island nor Newfoundland and Labrador.

Distribution

Largemouth Bass are native to the fresh waters of eastern-central North America, including the lower Great Lakes and some inland waters of southern Ontario. However, they have been widely introduced to other regions and are now one of the most widely distributed freshwater fish in the world, mainly because of their popularity as sport fish.

Habitat

Largemouth Bass prefer warm water and are usually found in small, shallow lakes or shallow bays of larger lakes. They are often found close to dense aquatic vegetation (e.g. cattails, waterlilies and submerged aquatic plants, such as pondweed) or other forms of cover, such as sunken logs.

Unlike Smallmouth Bass, Largemouth Bass are rarely found in rocky areas. Therefore, the habitats of Largemouth and Smallmouth Bass often do not overlap, even if both species inhabit the same lake.

Impacts

Largemouth Bass are top predators that can dramatically change native food webs after being introduced to a new waterbody. They are visual feeders and take food from the surface, in the water column and off the bottom of lakes. When established in new areas, Largemouth Bass can:

  • change the food web by reducing the amount of prey available to native fish
  • reduce or cause the local extinction of native fish populations or cause them to alter their behaviour

There are many factors that make Largemouth Bass a successful invader, including their:

  • fast growth rate
  • dietary flexibility
  • tolerance of high water temperatures and water cloudiness (turbidity)

Largemouth Bass.

Jaw of the Largemouth Bass

The jaw of the Largemouth Bass extends well behind the back margin of the eye when mouth is closed.

Separation between the two dorsal fins of Largemouth Bass

The separation between the two dorsal fins of Largemouth Bass is more pronounced than in Smallmouth Bass.

Irregular bars on a a Largemouth Bass

Largemouth Bass have irregular bars that form a horizontal stripe along their side.

Juvenile (young) Largemouth Bass

Juvenile (young) Largemouth Bass with irregular bars that form a dark horizontal stripe along their side.

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