Sturisoma nigrirostrum

The body of this catfish is very long, thin, and fully protected by ossified dermal plates arranged in longitudinal series. The dorsal profile is straight while the belly is flat. The head, triangular in dorsal view, extends into a widened and depressed rostrum. The maximum size observed for this species is around 24 cm in standard length (without the tail), approximately 30 cm in total length.

The base color is brown or dark yellow on the antero-dorsal part, becoming pale yellow on the ventral face. A dark dorso-lateral band runs from the tip of the snout, through the eye, and extends along the lateral line to halfway of the caudal peduncle, without reaching the caudal fin. The ventral face of the rostrum is uniformly dark, blending with these lateral bands. The dorsal, pectoral, pelvic, and anal fins are hyaline (transparent). The caudal fin has a dark longitudinal strip along the first two lower branched rays. The species lacks an adipose fin.

Adapted to benthic life, this fish has a mouth transformed into a ventral oral disk, allowing it to firmly grip substrates and stay in the current while grazing. Confined to small to medium-sized rivers with soft bottoms, it moves with agility thanks to its long anal fin and prehensile tail.

Like most Loricariinae, it assumes a resting posture clinging to supports (wood, rocks, vegetation), using its tail to balance.

The mouth morphology and tooth structure (fine, bifid, and numerous teeth) suggest an herbivorous and detritivorous diet. The species actively grazes on periphyton, filamentous algae, biofilms, and organic detritus deposited on sandy or muddy bottoms and submerged substrates.

As with other Loricariidae, spawning likely occurs on a hard substrate or partially buried, with male guarding the eggs until hatching.

The highly elongated body morphology suggests that the male wraps its tail around the spawn to protect and oxygenate it, a typical behavior of the Sturisoma genus.