The Largemouth Bass (Micropterus salmoides) and the Smallmouth Bass (Micropterus dolomieu) are two of the most popular freshwater game fish in North America. Both belong to the sunfish family, Centrarchidae, and are collectively known as “black bass.” While they share a common lineage, their appearances and habits differ significantly. Understanding these distinctions provides a clearer method for identifying which species is on the line or which type of water to target.
The Most Definitive Physical Traits
The quickest and most reliable way to differentiate the two species involves examining two primary structural features: the jawline and the dorsal fin. The size of the mouth is the most obvious identifier. When the mouth is closed, the upper jaw of the Largemouth Bass extends noticeably past the rear edge of the eye. This feature allows the Largemouth’s mouth to open much wider, which is why it is often called a “bucketmouth.”
In contrast, the jaw of the Smallmouth Bass typically ends directly beneath the center of the eye or only slightly behind it, making its mouth appear proportionally smaller relative to its body size.
Another reliable distinction is the dorsal fin. The Largemouth Bass possesses a deep, nearly complete separation between its spiny anterior dorsal fin and its soft posterior dorsal fin. This division makes the Largemouth’s dorsal fin appear almost like two separate fins. The Smallmouth Bass, however, has a continuous dorsal fin with only a shallow notch separating the spiny and soft sections.
Color Patterns and Body Shape
While the jaw and dorsal fin offer structural identification, coloration and overall body shape provide secondary visual cues. The Largemouth Bass typically exhibits a dark, olive-green body with a prominent, dark horizontal stripe or a series of dark blotches running along its lateral line from the gill plate to the tail.
The Smallmouth Bass, often referred to as a “bronzeback,” generally has a body color ranging from brownish-green to a rich bronze, lacking the distinct horizontal band. Instead, the Smallmouth usually displays dark brown vertical bars or mottled patterns along its sides. These markings help the fish blend into the rocky environments they prefer.
In terms of body structure, the Smallmouth Bass tends to be more streamlined and torpedo-shaped, built for navigating moving water and open spaces. The Largemouth Bass is generally bulkier and more elongated, with a larger head relative to its body.
Preferred Habitat and Water Conditions
The ecological preferences of the two species are the most significant difference outside of physical appearance, dictating where anglers can expect to find them. Largemouth Bass prefer warmer water temperatures, thriving in the range of 60 to 80 degrees Fahrenheit. They are often found in slow-moving or stagnant water bodies like ponds, lakes, and reservoirs, and they are more tolerant of murky or turbid water conditions.
These fish are classic ambush predators, showing a strong affinity for dense cover. They use heavy cover such as submerged vegetation (weed beds), fallen trees, brush piles, and boat docks to conceal themselves and quickly attack unsuspecting prey.
Smallmouth Bass prefer cooler, clearer water, with optimal temperatures ranging from 55 to 75 degrees Fahrenheit. They are commonly found in rivers with current, and in deep, clear lakes, where they gravitate toward hard, structured bottoms. Their preferred habitats include rocky shoals, gravel beds, boulders, and ledges. The Smallmouth is generally a more active hunter, chasing down prey in open water or around the edges of rocky structures.