Metadata

Notoglanidium pallidum

Roberts and Stewart 1976

Notoglanidium pallidum
Notoglanidium pallidum. Photograph by Melanie Stiassny, used with permission.
ORDERSUB-ORDERFAMILY
SiluriformesSiluroideiClaroteidae

Synonyms

None.

Country

Lower Congo River:fw

Types

Holotype: MCZ 50236.

Paratypes: MCZ 50294, BMNH 1976.5.21.24–25, MRAC 76-17-P-5–6, MCZ 50237, MCZ 76321, MCZ 50379.

Systematics

Notoglanidium pallidum was placed in the genus Platyglanis by Mo (1991). This placement was rejected in the revisionary study of Notoglanidium by Geerinckx et al. (2013).

There are nine species in the genus Notoglanidium Günther 1903: Notoglanidium akiri (Risch 1987), Notoglanidium boutchangai (Thys van den Audenaerde 1965), Notoglanidium depierrei (Daget 1980), Notoglanidium macrostoma (Pellegrin 1909),Notoglanidium maculatum (Boulenger 1916), Notoglanidium pallidum Roberts and Stewart 1976, Notoglanidium pembetadi Vreven, Ibala Zamba, Mamonekene and  Geerinckx 2013, Notoglanidium thomasi Boulenger 1916, Notoglanidium walkeri Günther 1903. Geerinckx et al. (2013) have two trees based on 24 morphological and osteological characters. They do not agree on the placment of N. pallidum. Their tree 1 has N. macrostoma as sister to the other eight species with N. pallidum sister to the other seven. Their tree 2 had N. pallidum and N. walkeri as sisters with N. macrostoma as sister to these two.

Roberts and Stewart (1976) say of N. boutchangai: "[Notoglanidium] boutchangai Thys 1965, [is] a microphthalmic, dorsally flattened fish of uniformly dark brownish coloration and a relatively high dorsal fin with seven branched rays, known only from the rapids of the riviere N gounie (Ogowe basin) near Lebamba, Gabon". (Emphasis added). It thus seems to be somewhat similar ecologically to N. pallidum.

Biological Notes

This is the description of Notoglanidium pallidum from the revisionary study of Geerinckx et al. (2013):

Notoglanidium pallidum Roberts & Stewart 1976
(Figs. 4C, 4D & 10F)

Holotype. MCZ 50236: Congo River near Bulu, west of Luozi, Democratic Republic of the Congo (Congo-Kinshasa); 5° 01’ S, 14° 01’ E; 53 mm SL (only images of specimen examined).

Paratypes. MCZ 50294: Congo River at Tadi, near Kibunzi, Democratic Republic of the Congo (Congo-Kinshasa); 5° 14’ S, 13° 56’ E; 5 out of 16 spec. examined, 19–83 mm SL. BMNH 1976.5.21.24–25: same locality; 2 spec., 40–63 mm SL. MRAC 76-17-P-5–6: same locality; 2 spec., 36–76 mm SL. MCZ 50237: same locality as holotype; 20 mm SL (not examined). MCZ 76321: same locality; two out of four cleared and stained spec. examined, 41–58 mm SL. MCZ 50379: Zaire River main stream a few km northeast of Kinganga; 73 mm SL (not examined).

Diagnosis. Notoglanidium pallidum differs from other species in the genus in having: a small eye diameter (3.8–7.0% HL) [vs. larger in N. boutchangai (7.5–10.4% HL), N. walkeri (7.8–10.6% HL), N. thomasi (9.1–12 5% HL) and N. macrostoma (9.1–13.3% HL)]; a small interorbital distance (20.0–23.3% HL) [vs. larger in N. akiri (24.1–32.8% HL), N. macrostoma (28.0–40.4% HL), N. maculatum (35.3–36.8% HL), N. thomasi (41.0–46.7% HL) and N. walkeri (27.8–33.3% HL)]; a small combined premaxillary tooth plate width (11.1–15.3% HL) [vs. larger (>18.2% HL) in N. akiri, N. boutchangai, N. depierrei, N. macrostoma and N. pembetadi]; an average number of soft dorsal-fin rays (8–10) [vs. seven rays in N. akiri, N. boutchangai and N. macrostoma, and >10 rays in N. maculatum (16–22), N. thomasi (12–16) and N. walkeri (11–15)]. Description. Both head and body dorsoventrally flattened, with depth almost constant from head to body (predorsal body depth 10.6–14.3% SL, minimal caudal peduncle depth 9.1–10.4% SL, head depth 9.8–13.8% SL). Branchiostegal membranes fused along anterior half only, with a slit separating the posterior halves (they may overlap). Adipose fin low (2.3–3.3% SL). See also Table 4.

Colouration in life. Pallid pink, without any markings (pale brownish when preserved).

Maximum size recorded. 81 mm SL.

Etymology. The species name indicates the pale (pallidus, Latin) skin of the species.

Distribution. Congo River west of Luozi, and more downriver at Tadi (Kibunzi; Fig. 13).

The lower Congo River, and especially the northern and southern rapids below Pool Malebo, are home to many endemic species (Roberts and Stewart 1976, Bailey 1986, Thieme et al. 2005, Mamonekene 2005, Alter et al. 2015, Alter et al. 2017, Stiassny 2016). In particular there are at least eleven species, in five Families, which exhibit the troglomorphic features of reduced eyes and pigment:

Clariidae

Channallabes apus (Günther 1873) Teugels 1986

Dolichallabes microphthalmus Poll 1942

Gymnallabes nops Roberts and Stewart 1976

Platyallabes tihoni (Poll 1944) Poll 1977

Claroteidae

Notoglanidium pallidum Roberts and Stewart 1976

Mastacembelidae

Mastacembelus aviceps Roberts and Stewart 1976

Mastacembelus brichardi (Poll 1958) Vreven 2005

Mastacembelus crassus Roberts and Stewart 1976

Mastacembelus latens Roberts and Stewart 1976

Cichlidae

Lamprologus lethops Roberts and Stewart 1976

Mormyridae

Stomatorhinus microps Boulenger 1898

These features probably evolved because these species live at depth within the rapids and spend their whole lives in permanent darkness, analagous to life in caves. The ocular and craniofacial anatomy of several of these species have been studied (Schobert et al. 2010, 2011, 2013) but almost nothing else is known about these animals.

Conservation Status

[VU D2:3.1:2010]

Moelants, T. 2010. Notoglanidium pallidum. The IUCN Red List of Threatened Species 2010: e.T182359A7868521. https://dx.doi.org/10.2305/IUCN.UK.2010-3.RLTS.T182359A7868521.en. Downloaded on 20 March 2020.

Museum Holdings

As above only.

Internet Resources

Africhthy.org

Main page for the Congo Project

Elizabeth Alter's work on Congo fishes

New York Times article with good photographs

Convergent evolution in the Congo rapids

A fish with the bends

Melanie Stiassny video presentation on the Congo River fishes

Key References

Roberts, T.R. and Stewart, D.J. Journal Article 1976 An ecological and systematic survey of fishes in the rapids of the lower Zaire or Congo river
Mo, T.-P. Journal Article 1991 Anatomy and systematics of Bagridae (Teleostei) and siluroid phylogeny
Geerinckx, T., Vreven, E.J., Dierick, M., van Hoorebeke, L. and Adriaens, D. Journal Article 2013 Revision of Notoglanidium and related gerera (Siluriformes: Claroteidae) based on morphology and osteology
Elbein, A. Web Page 2020 Earth’s deepest river conceals an evolutionary mystery