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Smallmouth Bass

Micropterus dolomieu

Identifying Characteristics

  • 20-38 cm long
  • slender, streamlined body with broad, slightly forked tail
  • body is generally brown, but varies depending on the environment
  • red to orange eyes
  • dark brown, vertical bands along the side
  • young have a yellow tail with black margin
This is an illustration of a Smallmouth Bass. 1 image
This is a map of British Columbia showing the spread of invasive species.

Watch it

This is an image of curator Gavin Hanke in a lab with bass specimens from the Royal BC Museum collection.
(Video 2:25 3.78 MB)

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Video transcript

Smallmouth and Largemouth Bass
Gavin Hanke, Curator, Vertebrate Zoology, Royal BC Museum

I’m Gavin Hanke, Curator of Vertebrate Zoology at the Royal BC Museum.

This is an image of bass specimens from the Royal BC Museum collection.

Both bass, the Smallmouth and the Largemouth, have a sizable mouth.  Largemouth Bass, even the young ones, here’s a very small one, have a band running right down the body.  Smallmouth Bass have vertical bars, this one’s fading, in fact all pickled specimens fade.  But Smallmouth Bass have vertical bars on the body.  Largemouth  have a long band down the side.  
This is an image of Dr Gavin Hanke, Royal BC Museum curator and Smallmouth Bass.
And you can also look at the length of the mouth, on a Largemouth, the upper jaw extends back behind the eye. On a Smallmouth it doesn’t.

This is an image of a Smallmouth Bass specimen preserved.

They are quite obvious when you see them, especially fresh ones. With the preserved ones it’s a little more difficult. They are distinctive.  

As an invasive species, they reproduce very well. So, their populations are growing quite quickly assisted by people moving them around the province. They’ve got a large mouth, that’ll tell you more or less that they are a predator.  

Imagine tadpoles, fish, aquatic insects, crayfish, anything that they could swallow, they will. I’ve seen these guys eat frogs, small mice, if a bird landed on the water, a really small bird, they would eat it. I’ve even had one in an aquarium that would eat french fries. They eat anything. Whatever comes close, they will eat.

They are also very territorial. So, when they are breeding, they defend an area, they create a nest and they will evict anything that comes near them.

This is an image of a two Smallmouth Bass specimen preserved.

Even a snail won’t be tolerated, they’ll grab a snail and push it out of the nest area. Any fish that comes near will get thrashed, they are quite aggressive.  

That severely disrupts the native eco-system.  You’ve got habitat and fauna that has evolved over the last few thousand years with a new gluttonous predator added. That really will change things.  
This is an image of a jar of fish with labels from the Royal BC Museum collection preserved.
The real issue is how they are getting spread around. People like them for fishing, so they move them around and will take a bucketful of bass to a new lake. We are really helping them move around the province.  If you introduce a new predator like that it will severely disrupt the system. 

Report a Sighting

An invasive with a mouth to match an appetite.

Despite the name, the Smallmouth Bass has a large mouth to match an even larger appetite. It is a favourite of anglers who illegally stock bass in lakes and rivers. Bass eat mostly small fish, amphibians, crayfish and aquatic insects. They swallow their prey whole, and their mouth is lined with small teeth that hold slippery prey like Velcro. The mouth and gills work together to suck in vast quantities of water, making escape even more difficult for unwary aquatic organisms. Even small mammals swimming on the surface are in danger if a sizable smallmouth is lurking nearby.

Impact on Communities and Native Species

Smallmouth Bass are aggressive predators. They out-compete native fish, such as Cutthroat and Rainbow Trout, for territory and prey, and eat any bite-sized native fish they encounter - even the prickly Threespine Stickleback. As well, they pose a threat to native freshwater insects, crustaceans, amphibians, young snakes and turtles, and small mammals. Smallmouth Bass are spreading in British Columbia thanks to human assistance, and are a threat not only to freshwater biodiversity, but also to fish that support commercial and recreation fisheries.

Invasion History

The Smallmouth Bass arrived in British Columbia in 1901 as fry or fingerlings, planted in lakes on Vancouver Island and on the mainland. Now the fish, native to eastern North America, are established in lakes on Vancouver Island, the Gulf Islands, and in the Kootenays, the Okanagan, the Thomson-Nicola and, most recently, the Cariboo regions. The Smallmouth Bass has spread both naturally, moving through rivers and streams to new lakes, and with the help of fishermen, who released bass into lakes to establish private fishing opportunities.