Fish
Largemouth Bass
Micropterus salmoides · also called black bass, bucketmouth, green trout
The largemouth bass is the fish that built an industry. It is not the biggest freshwater fish or the fastest, but it is aggressive, widespread, and endlessly catchable, and around it has grown a multi-billion-dollar world of boats, lures, and tournaments. It is also, outside North America, a serious invasive threat.
Overview
Micropterus salmoides is native to eastern and central North America and has been stocked into more than 70 countries. It is an olive-green ambush predator of weedy, warm, still water, typically 30–45 cm and up to a couple of kilograms, with trophy fish over 4.5 kg. Its huge mouth — the upper jaw reaches past the eye — gives it its name.
How it hunts
The bass waits in cover — weed beds, sunken timber, docks — and lunges out at passing prey, then returns. It eats fish, crayfish, and frogs, and a big one will also take ducklings, snakes, and rodents at the surface.
Nest guard and quick learner
The male builds and guards a nest, defending the eggs and fry for weeks. In heavily fished waters, bass become measurably harder to catch — a partly heritable wariness selected for by decades of catch-and-release.
Status
The largemouth bass is Least Concern and abundant. The real concern is where it has been introduced, where it frequently harms native fish and amphibians.
Largemouth Bass: common questions
What is the difference between largemouth and smallmouth bass?
They are close relatives, both members of the black bass group, but they differ in a few reliable ways. In the largemouth the upper jaw reaches back beyond the eye and the body usually carries a broad dark horizontal stripe; in the smallmouth the jaw ends below the eye and the sides show dark vertical bars. Largemouth prefer warm, still, weedy water such as ponds, lake shallows, and slow river backwaters, while smallmouth favour cooler, clearer, rockier lakes and moving rivers. Smallmouth are generally regarded as the harder fighter for their size, largemouth as the bigger fish and the one that drives the tournament industry.
Why is the largemouth bass such a popular sport fish?
Several things line up. It is widespread and easily stocked, tolerating warm water and low oxygen that would kill trout, so it can be established in farm ponds, reservoirs, and city lakes across most of a continent. It grows large, strikes lures aggressively, and fights hard with jumps and runs. It can be caught on a huge variety of methods, from live bait to elaborate artificial lures, which supports a large tackle industry. And it takes well to catch-and-release, so the same fish can be caught many times. Around this has grown a professional tournament circuit, televised coverage, and a boat and equipment market worth billions.
Do largemouth bass really eat ducklings and snakes?
Yes, though these are not everyday meals. A large largemouth is limited mainly by what will fit in its mouth, and its mouth is enormous. There is well-documented footage and stomach-content evidence of big bass taking ducklings, small grebes, frogs, water snakes, salamanders, mice and voles that fall in, and even small turtles, alongside the fish and crayfish that make up the bulk of the diet. The behaviour is opportunistic; a bass sitting under cover will explode on almost any struggling animal at the surface, which is exactly why frog and mouse imitation lures work so well.
Where is the largemouth bass an invasive species?
Almost everywhere it has been introduced outside its native North American range. Stocked for sport into lakes and rivers in Japan, South Africa, southern Europe, Central and South America, and many other regions, it preys heavily on native fish, tadpoles, and invertebrates that did not evolve with such a predator, and it has been implicated in the decline or local loss of endemic fish and amphibians in several countries. In Japan it is officially designated an invasive alien species with restrictions on moving or releasing it. Managing an introduced bass population is difficult once it is established.