Largemouth vs Smallmouth Bass: How to Tell Them Apart

Largemouth and smallmouth bass are both black bass, and they share a lot of water across North America. Size doesn't separate them. What does is a handful of features that hold true whatever the fish's age or the colour of the water. Work through these checks in order.

Check 1: where the upper jaw ends against the eye

This is the check state wildlife agencies put first. Hold the fish's mouth fully closed and look at it side on. Find the back corner of the upper jaw, the bony plate that runs back from the lip, and see where it sits against the eye.

• Largemouth: the upper jaw extends past the back edge of the eye. Open the mouth and you can see why they get called bucketmouths.
• Smallmouth: the upper jaw ends around the middle of the eye, and never clearly past the back of it.

Agencies word the smallmouth landmark slightly differently. North Carolina says the jaw reaches the middle of the eye. West Virginia says it does not go past the back of the eye. Both lead to the same answer. If the jaw clearly runs beyond the eye, it's a largemouth. If it stops under the eye, it's a smallmouth. Always check with the mouth fully closed, because that's how the identification charts measure it.

Check 2: a dark horizontal stripe or vertical bars

• Largemouth: a row of dark blotches that join up into an irregular horizontal stripe. The Wisconsin DNR describes it running from the eye to the tail.
• Smallmouth: no wide dark stripe along the side. Many show dark vertical bars down the flanks instead, and three dark bars running back from the eye.

These markings fade with age and can be faint on either species. A clear stripe or clear bars is a strong clue, but a plain-sided fish needs the jaw and fin checks.

Check 3: the dorsal fin notch

The dorsal fin on a bass's back has a spiny front part and a soft back part. How the two join is the third reliable check, and it shows up well in photos when the fin is raised.

• Largemouth: the two parts are almost separated by a deep notch, so it can look like two fins sitting side by side. The spiny front part has a jagged edge and the soft back part is rounded, like a paddle.
• Smallmouth: the two parts are joined, with only a shallow dip between them. It reads as one continuous fin.

Check 4: body colour (use it last)

• Largemouth: usually dark green on the back, lighter green on the sides and a pale belly.
• Smallmouth: usually bronze, brown or brownish green, which is where the nickname bronzeback comes from.

Colour is the weakest clue, so treat it as a tie-breaker. The Wisconsin DNR notes that largemouth from murky water are often dark brown or nearly black, while clear-water fish are lighter and brighter. Trust the jaw, the side markings and the fin first. We explain why colour fools people in How to Identify a Fish From a Photo.

Check 5: eye colour

The Wisconsin DNR describes the largemouth's eye as golden brown and the smallmouth's as red. Colorado says many smallmouth have a reddish eye, not all. A red eye points towards smallmouth, but it backs up the other checks rather than replacing them.

Habitat and behaviour

Where you caught the fish is a useful hint, though not proof, because the two species share plenty of lakes and rivers.

• Largemouth: warm, shallow, weedy water. Ponds, lake bays and slow river backwaters, close to cover such as weed beds, fallen trees, docks and stumps. The Wisconsin DNR says they are seldom found deeper than about 20 feet.
• Smallmouth: cooler, clearer water with rock and current. Rivers and streams with rocks, runs and pools, and the rocky parts of lakes and reservoirs. North Carolina notes they are rarely found in small ponds or lakes less than 25 feet deep, and tend to avoid water that is murky all the time.

How big do they get?

Largemouth grow bigger. George Perry's 22 lb 4 oz fish from Montgomery Lake, Georgia, caught in 1932, is still listed as the all-tackle world record. The smallmouth record is 11 lb 15 oz, caught by David Hayes at Dale Hollow Lake on the Tennessee and Kentucky border in 1955. Never use size to decide which species you have.

Watch out for spotted bass

In parts of the central and southern US there's a third common black bass, the spotted bass. It has a dark side stripe like a largemouth, but its jaw does not reach past the back of the eye. Missouri's Department of Conservation adds a second check: spotted bass have a rough patch of teeth on the tongue, which largemouth usually lack. If a fish has a stripe but a short jaw, it may be a spotted bass.

Quick comparison

• Upper jaw. Largemouth: past the back of the eye. Smallmouth: ends around the middle of the eye.
• Side markings. Largemouth: dark, blotchy horizontal stripe. Smallmouth: no stripe, often vertical bars.
• Dorsal fin. Largemouth: deep notch, almost two fins. Smallmouth: shallow notch, one joined fin.
• Body colour. Largemouth: green. Smallmouth: bronze, brown or brownish green. Both vary with the water.
• Eye colour. Largemouth: golden brown. Smallmouth: often red or red-brown.
• Habitat. Largemouth: warm, weedy, still or slow water. Smallmouth: cooler, clearer, rocky water with current.
• World record. Largemouth: 22 lb 4 oz. Smallmouth: 11 lb 15 oz.

Or photograph the fish in CastLog. It names the species, estimates the size and saves the catch to your private fishing diary with the spot and conditions. If a fish looks borderline, run the jaw and fin checks on your photo too. New to bass? Start with our largemouth bass fishing guide for beginners.

Questions

How do you tell a largemouth from a smallmouth bass by the jaw?

Close the mouth and look at where the upper jaw ends. On a largemouth it extends past the back of the eye. On a smallmouth it ends around the middle of the eye and does not go past the back of it.

Does a largemouth bass have a horizontal stripe?

Usually, yes. Largemouth have a row of dark blotches forming an irregular horizontal stripe along the side. Smallmouth have no wide stripe and often show vertical bars instead. Markings fade with age, so check the jaw as well.

Where does the smallmouth bass upper jaw end?

Around the middle of the eye. Wildlife agency charts describe it as reaching the middle of the eye, or as not extending past the back of the eye when the mouth is fully closed.