Roberts & Stewart (1976) in their work on the fishes of the lower Congo River reported the presence of two Micralestes in their collections: M. acutidens (Fig. 1A) and M. humilis (Fig. 1C). Recent collections in the region also include specimens of M. lualabae (Fig. 1D), M. stormsi (Fig. 1E) and M. holargyreus (Fig. 1B). In addition to these, a collection made in the vicinity of Inga revealed the presence of a population of diminutive alestid that appears most closely to resemble Micralestes but that are not assignable to any described Micralestes or to any other species dwarf African alestid.
Discussion. Recent collections in the region allow us to document the presence of six Micralestes in the stretch of the lower Congo River from Pool Malebo to Boma near the river’s mouth, and as an aid for field identification we provide here an illustrated key to those species.
1A Teeth with numerous small cusps, first inner row premaxillary tooth with 10-12 cusps (Key Fig. 1A). Inner row tooth pair on dentary usually multicuspid (Key Fig. 3A). Dorsal fin with distinctive black apical patch (Key Fig. 2A) .................................................................................................................. M. acutidens
1B Teeth with fewer cusps, first inner row premaxillary tooth with 6-8 cusps (Key Fig. 1B). Inner row tooth pair on dentary invariably unicuspid (Key Fig. 3B). Dorsal fin without black apical patch (Key Fig. 2B) ................................................................................................................................................................ 2
2A 23-28 scales in longitudinal series from opercle to point of caudal flexure (Key Fig. 2A) ........................ 3
2B 29-33 scales in longitudinal series (Key Fig. 2B) .................................................................... M. lualabae
3A Outer row premaxillary teeth small and tricuspid or quadricuspid (Key Fig. 1A) .....................................4
3B Outer row premaxillary teeth prominent, conical, or weakly shouldered, unicuspids (Key Fig. 1B) .......... ............................................................................................................................................... M. holargyreus
4A Median cusp of symphyseal teeth on dentary less than twice the height of adjacent cusps (Key Fig. 3A). 24-28 scales in longitudinal series from opercle to point of caudal flexure. Adipose fin black distally, pale proximally (Key Fig. 2A) ............................................................................................................................ 5
4B Median cusp of symphyseal teeth on dentary elongate and more than twice the height of adjacent cusps (Key Fig. 3B). 23-24 scales in longitudinal series from opercle to point of caudal flexure. Adipose fin black (Key Fig. 2B) ...................................................................................................................... M. stormsi
5A Relatively gracile, body depth 3.8-4.2 times into standard length. Adipose eyelid restricted posteriorly to orbital margin (Key Fig. 2A) ...................................................................................................... M. humilis
5B Relatively deep-bodied, body depth 3.0-3.8 times into standard length. Adipose eyelid extending posterodorsally over postorbital region (Key Fig. 2B) .............................................................................. M. schelly
Most of these species have widespread distributions encompassing most of the Congo basin and often also much of the rest of Central Africa (Poll, 1967). While we have not undertaken a revision of this genus and related taxa, a task that is ongoing, it is worthy of note that despite intensive collection and surveys in the region Micralestes holargyreus remains known only from the short stretch of the lower Congo River from Boma to Matadi, and M. schelly is only known from a single site in the vicinity of Inga. These two taxa are considered here to be lower Congo River endemics.
Micralestes is a genus of African tetras. There are currently 17 species in this genus.
Micralestes is a genus of African tetras. There are currently 17 species in this genus.
