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FACTSHEETS: May 2025 - no. 347

Denticetopsis praecox (Ferraris & Brown, 1991)

his month (May 2025) we are concentrating on the little-known family of Cetopsidae and catfishes that are not too well known in the hobby. Commonly known as "Whale Catfishes" because of the origin of the first name Cetopis, meaning "looks like a whale". Three pairs of barbels (no nasals); no adipose fin; swim bladder highly reduced and enclosed in bony capsule; dorsal fin far forward; anal fin with 20-29 rays. Five genera, Cetopsis, Cetopsidium, Denticetopsis, Helegenes and Paracetopsis.

There are 43 described species (2025) in this family and they are not too popular in the hobby due to their inactivity in the aquarium. One member of this genus the "Candiru" is a voracious predator of other wounded fish in its habitat, burying into the animal's flesh.

Denticetopsis praecox

Originally Denticetopsis as described by Ferraris in 1996, was restricted to two species, D. royeroi and D. sauli. These two species have proved to be a subunit of a larger clade that also includes two species previously assigned to the now invalid genus Pseudocetopsis (D. macilenta, D. praecox), together with three species described as new in 2005 (D. epa, D. iwokrama, D. seducta).

Denticetopsis can be differentiated from all other members of the Cetopsinae by the following features. The caudal-fin margin is either shallowly-forked or obliquely-truncate with the outer most rays no more than one and one-half times the length of the inner most rays (versus one and three-quarters to two times that length in other genera of the Cetopsinae). The medial most pelvic-fin ray has a membranous attachment to the body for the basal one-third to one-fourth of its length (versus an attachment more typically along the basal one-half of the ray, respectively). The possession of a first pectoral-fin ray that is spinous for the basal one-half of its length further separates Denticetopsis from Cetopsis and Paracetopsis both of which lack a spinous first pectoral-fin ray. Denticetopsis is further distinguished from Cetopsidium in the lack of the dorsal-spine locking mechanism that is present in the latter genus and in the having a lateral line extending either only onto the abdomen or distinctly further posteriorly onto the caudal peduncle (versus terminating above the base of the anal fin, receptively), (Vari, R.P., C.J. Ferraris, Jr. and M.C.C. de Pinna 2005).

Denticetopsis praecox - head view

The Cetopsinae have a relatively broad latitudinal distribution extending from northern Colombia to central Argentina and components of the subfamily also occur in river systems to both sides of the Andean Cordilleras. In Trans-Andean South America, species of the Cetopsinae occur along the Pacific Ocean versant of the continent from the Río Tumbes of northwestern Peru north to the Río Jurubidá of Colombia. Along the Caribbean Sea versant of that region members of the subfamily occur from the Río Sinú of northwestern Colombia to the Lago Maracaibo basin of northwestern Venezuela. East of the Andean Cordilleras members of the Cetopsinae occur in the Río Aroa and Río Yaracuy basins of the Caribbean Sea versant of northern Venezuela, across the Río Orinoco system and the coastal rivers of the Guianas, and south through the breadth of the Amazon basin and into portions of the Río de la Plata system. Along the eastern portions of South America, species of the Cetopsinae occur in the Rio Juquiá basin of the state of São Paulo and in the Rio São Francisco system, but with the possible exception of the Rio Gurupi of northeastern Brazil are unknown from the numerous remaining, independent basins draining into the Atlantic Ocean in the broad expanse between the mouth of the Rio Amazonas and the lower portions of the Rio Paraná (Vari, R.P., C.J. Ferraris, Jr. and M.C.C. de Pinna 2005).

Rio Baria

Distrbution: Venezuela; Baria River, Upper Negro River basin. Type locality: Neblina base camp, Río Mawarinuma of the Río Baria drainage, Territorio Federal Amazonas, southern Venezuela, 0º55'N, 66º10'W, elevation 120 m.

The Baria River in Venezuela is located within the Rio Negro basin, and specifically the Upper Negro River basin. It's a river that flows into the Rio Negro, a major tributary of the Amazon River. The Rio Negro itself is known as the largest blackwater river in the world. D. praecox have been found in a cobble-pebble habitat of black water streams that ranged in pH from 4.3–5.0.

Common Name

None

Synonyms

Pseudocetopsis praecox

Family

Cetopsidae

Subfamily

Cetopsinae

Distribution

South America: Venezuela; Baria River, Upper Negro River basin. Type locality: Neblina base camp, Río Mawarinuma of the Río Baria drainage, Territorio Federal Amazonas, southern Venezuela, 0º55'N, 66º10'W, elevation 120 m.

Size

5.5cm. (2¼ins)

Temp.

22-26°c (71-79°f)

p.H.

5.0-6.5.

Characteristics

Dorsal spines (total): 1; Dorsal soft rays (total): 6; Anal soft rays: 25 - 30; Vertebrae: 39 - 40.

Colouration

Readily distinguished from other members of the genus by its colour pattern consisting of a dark brown dorsum, speckled to dark sides, light venter, pale fins and a large dark spot on the basal half of the dorsal fin.

Aquarium Care & Compatibility

Not much is known on keeping this genera in an aquarium set-up but the litle information states that they spend most of the day in caves and only come out in the dark to feed. Provide a sandy substrate with pipes/caves and a swift current in the water for this species.

Reproduction

Unreported

Sexual differences

Males are somewhat smaller and have filament extensions to the dorsal and pectoral fins.

Diet

Feeds mostly in their natural habitat on aquatic insects. Bloodworm and other insect larvae would be a good food in the aquarium.

Glossary of Terms

Anal fin: The median, unpaired, ventrally located fin that lies behind the anus, usually on the posterior half of the fish.
Barbels: Whisker-like structure on the heads of most catfish.
Caudal fin: The tail.
Caudal peduncle: The narrow part of a fish's body to which the caudal or tail fin is attached.
Dorsal fin: The primary rayed fin(s) on top of the body.
Dorsum: The upper (dorsal) surface of the head or body.
Pectoral fin: The paired fins just behind the head.
Pelvic fin: The paired fins, between the pectorals and the anal fins (also referred to as ventrals).
Swim Bladder: The air sac that gives fish buoyancy and balance. Acts as sound resonator in some fish.
Vertebrae: The bones of the axial skeleton; divided into two sections, precaudal and caudal vertebrae.

Etymology

Denticetopsis: dentis (L.), tooth, referring to elevated symphyseal teeth of dentary; Cetopsis, type genus of family.
praecox: Derived from the Latin precocious, in reference to the small size of this species at sexual maturity.

References

Evers, H.-G. & I.Seidel: Mergus, Baensch Catfish Atlas Volume 1, 1st English edn., 2005. Pp.944.
Ferraris, C.J. Jr., 2007. Checklist of catfishes, recent and fossil (Osteichthyes: Siluriformes), and catalogue of siluriform primary types. Zootaxa 1418:1-628.
The ETYFish Project Fish Name Etymology Database © Christopher Scharpf.
Varella, H.R. 2023. Denticetopsis praecox. The IUCN Red List of Threatened Species 2023.
Vari, R.P., C.J. Ferraris, Jr. and M.C.C. de Pinna 2005 The neotropical whale catfishes (Siluriformes: Cetopsidae: Cetopsinae), a revisionary study. Neotrop. Ichthyol. 3(2):127-238.

IUCN Red List

Denticetopsis praecox is known from the Río Baria of the upper Río Negro basin in southern Venezuela and recent records in collections expand the distribution of the species to the Ventuari and Casiquiari drainages (Río Orinoco basin) in Venezuela. Some localities lie along the border of protected areas (Cerro de Neblina Base Camp-Venezuela/Parque Nacional Pico da Neblina-Brazil). Although the known distribution of the species is not wide, there is no evidence of a direct threat affecting the species. Therefore, Denticetopsis praecox is assessed as Least Concern (LC). (IUCN 2023).

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ScotCat Sources

Etymology-genus name

Etymology-specific name

Other Sources

Fishbase

Wikipedia

Catalog of Fishes

GBIF

FishNet2

iNaturalist

IUCN