Rock and warmouth bass look so much alike that it can be tough to tell them apart at a glance.
Both species share red eyes, similar body shapes, big mouths, and unbroken dorsal fins. And even their scale coloration can be similar enough that, at a glance, it’s tough to tell which you’ve caught.
But there are methods of positive identification that don’t require a degree in marine biology.
Below, we’ll dive into those differences so that you can positively identify both the rock and warmouth bass.
So keep reading!
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Rock Bass Basics
The rock bass is known to biologists as Ambloplites rupestris, and though its common name includes “bass,” it isn’t in the same genus or species as the largemouth or smallmouth. Smaller by far than either of these fish, the rock bass is really a panfish, and its nicknames suggest just that.
Fish in its native distribution, and you’ll hear the rock bass called names like “rock perch,” “goggle-eye,” “red eye,” and “black perch.”
Rock bass aren’t as geographically distributed as the largemouth. They call the St. Lawrence River and Great Lakes system home and thrive in the upper and middle Mississippi River basin as far south as Arkansas. Anglers in the east are blessed with them, too, and from New York through Kentucky and Tennessee down to Florida, you can find rock bass in abundance. Even Texas is in on the game, with the Nueces River system providing a home for this species.
Rock Bass Identification
The rock bass does look a bit like a miniature smallmouth, so it’s easy to see how it earned its common name.
But a closer look reveals distinct differences.
The rock bass’s dorsal fin is connected, with a spiny front portion and a soft, fan-shaped rearward portion. Dark red eyes are a sure giveaway, as are dark spots on its goldish-green sides. But these features won’t let you tell the difference between a rock bass and the warmouth bass.
One feature that will is the number of spines on the anal fin: rock bass have six.
Like smallmouth, rock bass prefer clear water and rocky bottoms. But like largemouth, they seek out plenty of aquatic vegetation.
They’ll call clear rivers and streams their home, as well as rocky-bottomed lakes, especially near shore.
Rock bass compete with smallmouth in habitats with flowing water, sharing a similar diet of small fish, crustaceans, and marine invertebrates. But despite voracious appetites, these small fish grow to a record maximum of about 3 pounds.
Warmouth Bass Basics
Lepomis gulosus, as the warmouth bass is known to science, isn’t a close relative of the rock bass, or for that matter, the small- and largemouth bass either.
Native to a larger geographical distribution than the rock bass, the warmouth inhabits lakes and rivers in the southern Mississippi River drainage. Present from the Gulf and Atlantic coasts as far north as the Chesapeake Bay and west to Texas’s border with Mexico, this hardy fish even thrives as far north as the Great Lakes basin.
Warmouth bass are very low-oxygen tolerant, making homes in waters where rock bass simply can’t survive. They prefer muddy bottoms and turbid water, inhabiting slow-moving streams, muddy ponds, and swamps.
Known by diverse nicknames, you’ll hear the warmouth bass called “Redeye,” “Goggle-eye,” “Red-eyed Bream,” “Stump Knocker,” “Mudgapper,” “Mo-mouth,” “Morgan,” “Molly,” “Rock Bass,” “Open Mouth,” “Weed Bass,” “Wood Bass,” “Strawberry ‘perch,” and “Mud Bass.”
And therein lies the problem.
The warmouth is commonly mistaken for the rock bass, and you’ll need to look carefully to distinguish them.
Warmouth Bass Identification
Warmouth bass share the connected dorsal fin - with both a spiny and soft section - with the rock bass. And they have the same dark red eyes.
The male warmouth, however, sports a bright orange spot at the back of the dorsal fin where it meets the body. Their scale coloration tends toward a dark, mottled brown rather than the bright green-gold of the rock bass. And you’ll often find a series of dark stripes on the face on the warmouth.
But the most certain what to know you’ve got a warmouth bass and not a rock bass is to count the spines of the anal fin: warmouth bass sport three.
Aggressive predators, the warmouth bass feeds on small fish, invertebrates, and crawfish. Typically a bit larger than the rock bass, they can grow to more than 12 inches and weigh as much as 2.25 pounds.
Rock Bass vs. Warmouth Bass
Is this a Rock Bass or Warmouth Bass? How do you know?
Is this a Rock Bass or a Warmouth Bass? How do you know?
The first cue to positive identification is to ask yourself about the water conditions.
- Rock bass prefer rocky bottoms and clear water, as their name suggests.
- Warmouth bass prefer muddy bottoms and muddy, stained water.
The second thing to look for is the presence of a bright orange spot (for males) at the base of the dorsal fin. If you don’t see that, examine the head carefully for the distinctive horizontal stripes of the warmouth, as well as a generally dark coloration.
But the only way to be absolutely sure is to count the anal spines: warmouth have three; rock bass have six.
Rock bass
- golden-green scales with dark spots
- red eyes
- continuous dorsal fin with a spiny front and soft back
- six spines on the anal fin
Warmouth bass
- mottled, dark brown scales, sometimes with vertical bars
- red eyes
- continuous dorsal fin with a spiny front and soft back
- males will have a bright orange spot at the rearward base of the dorsal fin
- dark, horizontal striped on the face
- three spines on the anal fin
Final Thoughts
Positive identification is important for every species, and knowing what you’ve caught is essential for any angler.
We hope that this article has helped you learn to tell the difference between a Rock Bass and a Warmouth Bass, and if it has, we’d love to hear from you.
Please leave a comment below.
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