Hypophthalmus

''Hypophthalmus'' is a genus of long-whiskered catfishes native to freshwater in tropical and subtropical South America.

Species

There are currently 4 recognized species in this genus:
* '' Hypophthalmus edentatus'' Spix & Agassiz, 1829 (Highwaterman catfish)
* ''Hypophthalmus fimbriatus'' Kner, 1857
* '' Hypophthalmus marginatus'' Valenciennes, 1840
* '' Hypophthalmus oremaculatus'' Nani & Fuster, 1947

Taxonomy

This genus has been classified within its own family Hypophthalmidae. However, it has since been reclassified as a member of Pimelodidae; it is thought to be most closely related to ''Parapimelodus''.

Distribution

''H. edentatus'' is found in the Amazon and Orinoco River basins and Atlantic coastal rivers of Guyana and Suriname. ''H. fimbriatus'' inhabits the Amazon River at Santarém and Rio Negro basin in Brazil and Venezuela. ''H. marginatus'' originates from the Amazon and Orinoco River basins and major rivers of French Guiana and Suriname. ''H. oremaculatus'' is distributed in the Paraná River basin, Brazil and Argentina.

Description

Fish of this genus have scaleless skin, three pairs of barbels (one maxillary and two mandibular), and small eyes located lateroventrally in a position about mid-length of the head. The body is laterally compressed, bearing a long-based anal fin that runs from the anus to the anterior margin of the caudal peduncle. The dorsal, pectoral, and pelvic fins have a narrow base and lack spines. The posterior margin of the caudal fin is either deeply forked or emarginate, depending on the species.

Ecology

''Hypophthalmus'' are unusual among Neotropical fishes in their habit of specialized plankton-feeding, collecting plankton by straining water over the fine sieve created by numerous long, thin gill rakers. ''H. edentatus'' feeds primarily on cladocerans, copepods, and ostracods. It also feeds on debris and other plankton. ''H. fimbriatus'' has a diet consisting primarily of zooplankton, especially cladocerans and copepods. On the other hand, ''H. marginatus'' feeds primarily on phytoplankton. ''H. edentatus'' appears to follow the vertical movement of plankton throughout the day.

''H. edentatus'' is a pelagic species which lives in schools near the surface of the water over muddy bottoms. Ovaries start to develop in November when the water level starts to rise. Fractional spawning occurs between February and April. The female lays down 50,000 to 100,000 eggs according to body weight. Juveniles inhabit the lower part of streams in estuaries, while adults are found more upstream.

''H. edentatus'' and ''H. marginatus'' are more common in clear and whitewater habitats and are extremely limited or nonexistent in blackwater habitats. ''H. edentatus'' and ''H. marginatus'' occur in some of the same habitats; however, ''H. marginatus'' are more common in river and creek channel habitats while ''H. edentatus'' are more common from aquatic floodplains, including seasonally flooded lagoons. ''H. marginatus'' has a forked caudal fin, which is more efficient in a habitat with faster moving water. ''H. edentatus'' has an emarginate caudal fin, which is less vulnerable to fin-nipping by piranhas which are more abundant in slow-moving waters. ''H. fimbriatus'' may be restricted to blackwater habitats. ''H. edentatus'' are most common in lagoons and floodplains during the dry season, and move into flooded savannas during the rainy season. ''H. marginatus'' prefers to stay in larger, permanent water bodies.

Fishing

''Hypophthalmus'' support important fisheries. Based on a review by IBAMA, they are the 9th most caught fish by weight in the Brazilian Amazon.Araujo-Lima, C.A.R.M.; and M.L. Ruffino (2004). Migratory Fishes of the Brazilian Amazon. Pp. 233—302 in: Carolsfeld, J.; B. Harvey; C. Ross; and A. Baer (editors). Migratory Fishes of South America.

References

{{Taxonbar, from=Q1863328

Pimelodidae
Fish of South America
Fish of the Amazon basin
Catfish genera
Taxa named by Georges Cuvier
Freshwater fish genera