Smallmouth Bass vs. Rock Bass: The Differences Explained

Photo Credit – @natural_land_fishing

Anglers hoping to score the best catch need to stay familiar with the different types of bass they may encounter while out on freshwater lakes and streams. With more than a dozen species and subspecies in North America alone, identifying your catch may be trickier than you think. Will you be able to tell the difference between a smallmouth bass and a rock bass?

Smallmouth bass and rock bass are very similar. They’re members of the sunfish family, and their habitat, diet, and mating habits are practically identical. However, the smallmouth bass is larger than the rock bass. Additionally, the rock bass has a spiny anal fin, while the smallmouth bass doesn’t.

Let’s explore these two bass types to discover what they look like, how they live, and how they differ from one another. 

What Are Smallmouth Bass?

The smallmouth bass (Micropterus dolomieu) is a freshwater fish native to North America. This species typically prefers cool temperate waters and is a favorite catch among sporting anglers. However, unlike other types of game fish, most anglers don’t consume the smallmouth basses they catch. 


Smallmouth basses come in a variety of exciting colorations. However, they’re primarily members of the black bass family. They tend to exhibit a dark green, yellow, or brown scaling with lateral black stripes across the body. 

These up-and-down strips become horizontal on the fish’s head, gills, and mouth. Interestingly, smallmouth basses seem to be capable of altering their coloration. They may look far darker during the mating season or when exhibiting dominant, territorial behavior. Still, smallmouth bass coloration tends to differ depending on the habitat and the local predators.

For example, a smallmouth bass living in a relatively shallow, sandy, and sunny location may exhibit brighter scales and minimal striping. Smallmouth basses living in pebbly rivers or leaf-strewn tributaries may develop darker patterns to help them remain camouflaged. 

This type of fish is also equipped with a handy defensive tool—a rigid, spiked dorsal fin that can flex inward toward the body or outward and away from the body. When a larger predatory fish attempts to swallow a smallmouth bass, these fins turn outward. 

Photo Credit – @wyattsreelfishing

This motion causes damage and potentially allows the bass to escape hungry predators’ jaws, including the beaks of voracious birds. Though many anglers may believe that all smallmouth basses have dark brown, gold, or black eyes, some are known to have bright red eyes


Specimens living in large freshwater bodies (such as lakes or wide, deep rivers) may grow up to about two feet (61 cm) in length, which rivals the size of juvenile largemouth bass. This sizing can make identification challenging but not impossible.

Due to global trade, smallmouth bass can be found worldwide, particularly in self-contained freshwater fish farms. The fish produced in these facilities aren’t often harvested for food. Instead, they’re released into rivers, streams, and lakes to boost native populations and ensure a good fishing season for anglers.

Adult smallmouth basses tend to reproduce in shallow waters, and juvenile basses tend to stick around their gravelly nest until they’re about two weeks old. To ensure the young bass fry’s survival, male smallmouth basses guard their nests until move-out time. 

The majority of smallmouth basses prefer to live in freshwater environments with clean, clear water and rocky bottoms. Rivers, lakes, and streams are all popular housing choices for smallmouth basses.


The smallmouth bass has a favorite meal, and anglers might do well to remember this sporting fish’s preferred breakfast, lunch, and dinner: Crayfish (also known as crawfish and crawdads). That’s right! Smallmouth basses enjoy the sweet, slightly-fishy taste of crawdad just as much as the average New Orleans native. 

However, basses don’t mind filling their bellies with other types of snacks between available crawfish meals. They often consume insects, insect larvae, and smaller fish. In this way, the smallmouth bass is opportunistic and somewhat omnivorous. 

What Are Rock Bass?

The rock bass (Ambloplites rupestris) is known by many names. Some call it a red eye, and others may call it a rock perch. Adventurous anglers may even call the rock bass ‘the goggle-eye fish.’ Still, no matter which title you prefer for this aquatic creature, it’s neither a type of perch nor a redeye bass. 

Rock basses are part of the sunfish family. This relation makes them close cousins of the smallmouth bass, but rock basses have at least one notable feature that sets them apart from their genetic relatives. 


Rock basses look very similar to other types of bass and sunfish. However, their extra anal fin spines do set them apart. This defining feature is beneficial, as the scale coloration on a rock bass can vary widely. 

Unlike smallmouth and largemouth bass, the rock bass has a slightly boxier, stouter body. It’s a bit shorter than other bass species, and most rock bass barely weigh-in at a single pound. While you may think that this petite quality makes the rock bass an unlikely dinner fish, anglers tend to keep and cook rock bass far more frequently than smallmouth bass.

The average rock bass can be green, brown, yellow, and white. As with other sunfish, specific coloration may partially derive from the environment. The brighter and more shallow a rock bass’s habitat, the more likely it is to have bright, lighter-colored scales. 

Even in the largest water bodies, rock basses don’t ever get close to reaching the average length of smallmouth basses. This revelation is an interesting one, as rock bass often share their habitat with other types of bass, including the smallmouth variety.


Rock basses tend to dwell in freshwater streams, rivers, and lakes, much like other bass types. They lay their eggs in pebbly areas, and the males aggressively defend their offspring until they’re old enough to survive on their own.

Because rock basses share their habitat with many other freshwater fish, they tend to compete for resources. One of the only saving graces of the rock bass that allow it to flourish and survive en masse is its spiny anal fin. 


Like the smallmouth bass, rock basses prefer a varied diet of insects, insect nymphs, smaller fish, and available crustaceans. However, they’re slightly lower on the food chain than the smallmouth bass. This positioning is partially due to the rock bass’s smaller size. 

As such, rock basses may work hard to avoid crossing paths with larger smallmouth basses. Of course, if they end up on the wrong end of a fellow fish’s mouth or beak, they can employ both their spiny dorsal and ventral fins. After getting several spines to the throat, the offending predator might simply cough its meal back up and wander away.

Still, rock basses may subsist on the leftovers of larger, more aggressive freshwater fish. This trend may contribute to the consistently petite size of the rock bass.

Smallmouth Bass vs. Rock Bass: How Are They Different?

There are two primary differences between smallmouth basses and rock basses. Firstly, the rock bass is a smaller, stouter fish than the leaner smallmouth bass. The average length of a rock bass is about eight inches (20.3 cm), but the average size of a smallmouth bass is about fourteen inches (35.6 cm). 

Secondly, the rock bass has an extended anal fin with rigid spines. This extra-long, uncomfortably sharp fin helps the rock bass survive predatory attacks, especially those coming from competing bass species. As such, the rock bass makes up for its diminutive size with upgraded weaponry.


Both the smallmouth bass and the rock bass belong to the sunfish family. They both live in freshwater habitats and prefer clean, clear waters. Both species feature aggressive males that protect their young. 

Rock basses are smaller than their smallmouth counterparts, and they also exhibit a spiny anal fin extension to help them ward away hungry predators, including nearby smallmouth basses!


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