What do they look like?

Micropterus salmoides has a large mouth, a notch between the two dorsal fins, and a dark stripe along the side of the body (Bailey et al., 2004). This black band is seemingly made up of small oval shapes to a closer eye. Coloration is variable, but is usually a darkish green on the back and sides, fading to an off-white on the belly. The anterior dorsal fin has nine to eleven spines while the posterior dorsal fin has twelve to fourteen rays (Boschung et al., 2004). The average weight of M. salmoides is one kilogram; however, certain individuals have reached weights of over ten kilograms. Males usually do not surpass 40 cm, while females can reach up to 56 cm in length.

Where in the world do they live?

Micropterus salmoides is native to eastern North America and historically ranged from southern Canada to northern Mexico, and from the Atlantic coast to the central region of the United States. Since the beginning of the twentieth century largemouth bass have been introduced successfully all over the world.

What kind of habitat do they need?

Largemouth bass prefer quiet, clear waters with abundant vegetation (Iguchi and Matsuura, 2004). More specifically, they prefer shallow water that is usually no deeper than 2.5 meters, but they sometimes occupy deeper regions. Abundant vegetation is important because it allows bass to hide from their prey and provides protection against predators. Their environment is also made up of regions of clear waters where the bass' vision can be utilized to detect prey.

How do they grow?

After hatching, which usually takes from three to four days, larvae form a school that moves with the close protection of a male adult. Once the individuals reach a length of almost three centimeters they leave the school to fend for themselves. At this point, the juveniles are approximately one month in age. From this point on their growth rate occurs at different speeds throughout their lives. During the first year, largemouth bass grow from 10 to 20 centimeters in length. Growth rate decreases every year, and after about five to six years there is very little change in length.

How do they reproduce?

During the breeding season, each male prepares and builds a nest in shallow water. Nests are generally very crude in design. Once the nest is built a female swims near, and following an act of courtship, she lay her eggs in the nest.

Micropterus salmoides breeds in the spring. This time is determined by the temperature of the water, which usually ends up being around 60 degrees Fahrenheit. Females lay their eggs in the nests of males, and males then guard the eggs until they hatch. On average there are about 3,000 fry per nest, but as many as 6,000 have been observed (Becker, 1983). Following hatching, the schooling fry remain close to their father for at most one month (Dewoody et al., 2000). Largemouth bass females reach sexual maturity at four to five months of age, and males reach sexual maturity at three to four months of age.

Female largemouth bass do not invest anything more than their gametes to their offspring. Males begin their investment by constructing nests as well as defending these nests from intruders. Once the eggs hatch males remain with their broods and defend them against all predators. This continues usually for about a month.

How long do they live?

Largemouth bass live much longer in the wild than they do in captivity. The longest known lifespan of a wild largemouth bass was 23 years. The expected lifespan in the wild, though, is around 15 years. In captivity the longest lifespan recorded was 11 years, while the average age of death in captivity is around 6 years.

How do they behave?

In the morning, largemouth bass tend to be very mobile and remain in deep waters (>2.5 m). In the afternoon, bass are sedentary and are usually found near a larger structure in deeper water. As the sun goes down largemouth bass become very mobile and move into shallow water. They remain active throughout the night with a slight decrease in mobility. Movement of bass usually correlates to movement of prey species. The home ranges of largemouth bass are relatively small and overlap with each other. Despite this, there is very little agonistic behavior between individuals and most interaction occurs during spawning.

Home Range

Home range size for M. salmoides ranges from 0.1 to 50 ha.

How do they communicate with each other?

Largemouth bass perceive their environment through visual, auditory, tactile, and chemical means, as do most fish.

What do they eat?

Immature Micropterus salmoides feed on zooplankton and aquatic insects. As they grow their diet shifts to crayfish and other fish species. Sunfish are the food of choice for most adult largemouth bass.

What eats them and how do they avoid being eaten?

Larval and juvenile largemouth bass are prey species of yellow perch, walleye, northern pike, and muskellunge. As adults, largemouth bass can usually escape most predators. The primary predators on adult largemouth bass are humans.

What roles do they have in the ecosystem?

Micropterus salmoides plays an important role in the ecosystem as a top predator. Top predators are important because they maintain the populations of all of the animals below them in the food chain. Their success is not limited by any specific type of prey. Instead, they prey upon a number of species, and therefore maintain the health and viability of the ecosystem.

Do they cause problems?

With its many introductions all over the world, M. salmoides has had many negative impacts on the native ecosystems. Two of the main impacts are the loss of biodiversity and the homogenization of ecosystems. Introduced poplulations also influence the densities of other sport fishes like trout and walleye. These issues are currently being studied and management plans are being implemented all over the world.

How do they interact with us?

Largemouth bass are important game fish. They are one of the most popular fishes to catch and they continue to bring popularity to the sport of fishing.

Are they endangered?

Micropterus salmoides does not find itself on any of the lists of endangered species around the world. In fact the largemouth bass is one of the most successful fish, not only in its native areas, but also in freshwater areas all over the world where it has been introduced. There are certain fishing regulations that are set upon the catching of largemouth bass and these differ among regions. They involve either a limit to the number you can catch, a limit on the size that you can keep, or regulations on the season of the year in which you can catch them.

Contributors

Allison Poor (editor), University of Michigan: December, 2005.

Ryan Curtis (author), University of Michigan: October, 2005. Kevin Wehrly (editor, instructor), University of Michigan: October, 2005.

References

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