Largemouth bass grow 4 to 6 inches (10 to 15 cm) during their first year, 8 to 12 inches (20 to 30 cm) in two years, 16 inches (40 cm) in three years. They are usually green with dark blotches that form a horizontal stripe along the middle of the fish on either side. The underside ranges in color from light green to almost white. They have a nearly divided dorsal fin with the anterior portion containing nine spines and the posterior portion containing 12 to 13 soft rays. Their upper jaw reaches far beyond the rear margin of the eye.

Micropterus is Greek, meaning “small fin” and is a rather unfortunate misnomer arising from an injured type specimen that made it appear that the posterior rays of the soft dorsal fin formed a small separate fin. Treculi refers to Trecul, the French compatriot of Vaillant and Bocourt. Trecul actually caught the specimen. The Guadalupe bass is generally green in color and may be distinguished from similar species found in Texas in that it doesn’t have vertical bars like smallmouth bass, its jaw doesn’t extend beyond the eyes as in largemouth bass, and coloration extends much lower on the body than in spotted bass.