Tetranematichthys wallacei Vari & Ferraris 2006

Wallace’s catfish (Tetranematichthys wallacei) live in acidic, blackwater streams and small rivers with very slow water flow, where they lurk among submerged logs and branches. This catfish is a member of the driftwood catfish family (Auchenipteridae), a group of small to mid-sized fishes living in the rivers and lowland lakes of much of South America. Wallace’s catfish has a broad distribution in the Orinoco and Amazon drainage basins, where it lives among branches and trees that have fallen into streams and small rivers where the fish's mottled brown coloration allows it to blend in with the background. The two barbels below the lower lip extend forward and have elaborations at their tips which may serve as lures to attract smaller fishes and other prey. Males of the species have the spine of the dorsal fin on the top of the body elongate and stiffened. The barbels in front of the eyes are also lengthened and stiff and along with the spine on the dorsal fin help to embrace the female during spawning.

Wallace's Catfish is named after Alfred Russel Wallace, who, along with Charles Darwin, is most often remembered as the co-“discoverer” of evolution by natural selection. Starting in 1848, Wallace made large collections of plants and animals in the Amazon basin. Although his collections were all lost when the ship carrying him back to England caught fire and sank, he saved his notebooks and drawings, one of which clearly shows the species now named after him.

(Vari and Ferraris 2006)

Diagnosis: Distinguished from T. quadrifilis in the alignment of the lateral margins of the head in the region from the anterior margin of the orbit to the posterior limit of the opercle (running approximately in parallel from ventral view vs. diverging laterally, respectively); in the body width at the pectoral-fin insertion as a proportion of the head width at the posterior margin of the orbit (0.99-1.10 vs. 1.17-1.25, respectively); in the distance from the tip of the snout to the anal fin origin (0.29-0.32 of SL vs. 0.33-0.36 of SL, respectively); and in the position of the anterior termination of the gill opening (one orbital diameter posterior of the transverse plane running through the posterior margin of the orbit vs. positioned in the transverse plane running through the center of the orbit, respectively) (Ref. 56964).

The holotype (MZUSP 31096) was reported to have been collected in an acidic, slow-flowing, blackwater igarape within the flooded rainforest. Habitat information is lacking for most of the other examined specimens; however, several of the paratype lots (USNM 269994, USNM 269995, USNM 27008) were captured in still rain forest backwaters or in shallow rain forest streams with sandy bottoms and barely perceptible water flow; characterized by blackwaters and numerous submerged logs and branches. Specimens collected in the lower Rio Ucayali basin in northeastern Peru and the region of the Rio japura in Amazonas, Brazil, but not examined in this study, were similarly associated with submerged logs (Ref. 56964).