Enteromius alberti (Poll, 1939)

Maetens, Heleen, Steenberge, Maarten Van, Snoeks, Jos & Decru, Eva, 2020, Revalidation of Enteromius alberti and presence of Enteromius cf. mimus (Cypriniformes: Cyprinidae) in the Lake Edward system, East Africa, European Journal of Taxonomy 700, pp. 1-28 : 15-18

Enteromius alberti (Poll, 1939)

Fig. 7 a–b, Table 2

Enteromius cercops ( Whitehead, 1960) (here synonymised). syn. nov.

Diagnosis

Enteromius alberti ( Fig. 7 a–b) belongs to the group of species of Enteromius with a flexible last unbranched dorsal fin ray that lacks serrations along its posterior edge. A comparison was made with other species of Enteromius from this group from the East Coast and Nilo-Sudan ichthyofaunal provinces (list made based on information available in, e.g., Greenwood 1962; Okaronon et al. 1997; Seegers et al. 2003; Schmidt et al. 2017; Froese & Pauly 2018). Enteromius alberti can easily be distinguished from the other species of this group from the East Coast and Nilo-Sudan ichthyofaunal regions by the following combination of characteristics (data from original description, unless otherwise stated): a complete lateral line vs an incomplete lateral line in E. atkinsoni (Bailey, 1969) , E. pumilus (Boulenger, 1901) , E. serengetiensis (Farm, 2000) , E. tongaensis (Rendahl, 1935) and E. toppini ( Boulenger, 1916) ; two pairs of barbels vs one pair in E. pseudotoppini (Seegers, 1996) , and no barbels in E. anema ( Boulenger, 1903) and E. profundus ( Greenwood, 1970) ; one to three dark spots on the flanks, which sometimes fuse into a mid-lateral line in preserved specimens, starting posterior to the operculum vs a dark line running from the tip of the snout to the caudal fin base in E. bifrenatus (Fowler, 1935) and E. yongei ( Whitehead, 1960) , and a thin dark line from the beginning of the operculum to the caudal fin base in E. viviparus (Weber, 1897) ; 12 scales around the caudal peduncle, with one aberrant specimen in the paratypes of E. cercops (16), vs 8 in E. leonensis (Boulenger, 1915) , 9–10 in E. venustus (Bailey, 1980) , and 10 in E. magdalenae (Boulenger, 1906) and E. yeiensis (Johnsen, 1926) ; 4.5 scales between the dorsal fin base and the lateral line vs 3.5 in E. radiatus (Peters, 1853) ( Greenwood 1970) , 5.5 in E. unitaeniatus (G̹nther, 1867), and 6 in E. usambarae (Lönnberg, 1907) ; a dorsal fin length which is larger than the head length vs a dorsal fin length equal to the head length in E. innocens (Pfeffer, 1896) ; a body depth which is larger than the head length vs a body depth which is equal to the head length in E. nigeriensis ( Boulenger, 1903) and E. trispilopleura (Boulenger, 1902) ; a pectoral fin length which is ⁵⁄₆ of the head length vs ¾ in E. lineomaculatus ( Boulenger, 1903) , and ¾ to ¼ in E. neglectus ( Boulenger, 1903) ( Boulenger 1907) ; a maximum caudal peduncle depth which is ³⁄₅ of the head length vs ²⁄ ₅ in E. quadripunctatus (Pfeffer, 1896) . Enteromius alberti differs from E. perince by a combination of a smaller body depth [21.7–31.2% SL (mean 26.9) vs 33.8–37.5 (35.0)], a smaller minimum caudal peduncle depth [10.0–13.6% SL (mean 12.0) vs 15.0–16.4 (15.5)], and a smaller maximum caudal peduncle depth [11.8–15.5% SL (mean 13.6) vs 17.7–19.4 (18.8)]. Enteromius alberti differs from E. stigmatopygus by a combination of a higher number of lateral line scales [27–34 (median 31) vs 20–25 (21)], a smaller pre-dorsal distance [45.7–51.3% SL (mean 49.0) vs 51.9–55.8 (53.8)] and a smaller pre-occipital distance [16.6-21.8% SL (mean 18.6) vs 22.1–27.3 (24.0)]. Enteromius alberti differs from E. mimus by a higher number of lateral line scales [27–34 (median 31) vs 24–27 (25)], a smaller pre-anal distance [65.1–73.0% SL (average 69.3) vs 68.4–74.8 (72.4)], a larger post-anal distance [16.3–24.2% SL (average 21.1) vs 16.3–19.3 (17.8)], a smaller body depth [21.7–31.2% SL (average 26.9) vs 26.5–34.3 (30.1)], a smaller head depth [15.1–19.0% SL (average 17.3) vs 17.8–21.8 (20.2)] and a smaller pelvic fin length [15.0–20.9% SL (average 18.0) vs 18.2–22.4 (20.4)] ( Table 2). Specimens of E. alberti differ from the population of E. cf. mimus from the Lake Edward system by a smaller head depth. In general, a specimen with a head depth smaller than 19% of the standard length can be assigned to E. alberti (only one specimen had a higher value). Specimens with a head depth larger than 19% of the standard length can be assigned to E. cf. mimus (only one specimen had a lower value). Other characters to distinguish E. alberti from E. cf. mimus are the higher number of lateral line scales [27–34 (median 31) vs 21–31 (26)], the smaller interorbital width [5.8–8.3% SL (mean 7.3) vs 6.9–9.9 (8.7)], the smaller pre-pelvic distance [44.8–53.3% SL (mean 49,2) vs 48.4–55.4 (52.1)], the smaller body depth [21.7–31.2% SL (mean 26.9) vs 23.5–35.8 (31.0)], the smaller maximum [11.8– 15.5% SL (mean 13.6) vs 8.7–19.0 (16)] and minimum [10.0–13.6% SL (mean 12) vs 7.1–15.9 (13.7)] caudal peduncle depth, and the smaller head width [10.4–14.2% SL (mean 12) vs 11.6–14.5 (13.2)] ( Table 2, Fig. 3 ).

Etymology

Etymology not explained in the original description. Probably, the species epithet alberti is derived from the name of the former ‘Parc National Albert’ (now Virunga National Park) in which the type locality is located.

Material examined

Lectotype (here designated)

DEMOCRATIC REPUBLIC OF THE CONGO • Rutshuru River , May-Ya-Moto ; 5–11 Nov. 1934; de Witte leg.; MRAC 64723 (Supplementary file SM.01: Fiche-209).

Paralectotype

DEMOCRATIC REPUBLIC OF THE CONGO • 1 spec.; same collection data as for lectotype; MRAC 64722 (Supplementary file SM.01: Fiche-210) .

Other material examined

KENYA – Lake Victoria basin • 1 spec., holotype of E. cercops ; Luambwa, Nzoia River, Nyanza Province ; 1960; BMNH 1960.6.7.37 • 7 specs [of 13 in lot], paratypes of E. cercops ; same collection data as for holotype; BMNH 1960.6.7.38 to 1960.6.7.50 (Supplementary file SM.01: Fiche-177 to Fiche-183) .

UGANDA – Lake Edward • 1 spec. [of 2 in lot]; Nchwera River , Rwenshama-Ishasha road; 0°27ʹ30.8ʺ S, 29°48ʹ07.0ʺ E; 8 Nov. 2016; HIPE exped.; GenBank: MT251114 ; RMCA 2016.035.P.0148 to 2016.035.P.0149 (Supplementary file SM.01: E31) .• 1 spec. [of 2 in lot]; same collection data as for preceding; RMCA 2016.035.P.0171 to 2016.035.P.0172 (Supplementary file SM.01: HP1028) .• 1 spec.; Kayanja, offshore, Lake Edward ; 0°05ʹ31.2ʺ S, 29°45ʹ30.3ʺ E; 20 Jan. 2018; HIPE exped.; GenBank: MT251133 ; RMCA 2018.008.P.0247 (Supplementary file SM.01: HP2599) .• 2 specs.; Nyamweru River, mouth, Kisenji ; 0°18′42.5″ S, 29°51′36.0″ E; 31 Jan. 2018; HIPE exped.; RBINS 25585 to 25586 (Supplementary file SM.01: Fiche-118, Fiche-119) – Lake George • 5 specs; River 2 km east of Kitongore; 0°05ʹ45.6ʺ S, 30°40ʹ51.6ʺ E; 31 Oct. 2016; HIPE exped.; GenBank: MT251105 , MT251120 , MT251121 , MT251106 , MT251107 ; RMCA 2016.035.P.0159 to 2016.035.P.0163 (Supplementary file SM.01: HP592, HP595, HP596, HP600, HP602) • 2 specs; Mpanga River , mouth, Lake George; 0°02ʹ20.4ʺ N, 30°17ʹ24.0ʺ E; 31 Oct. 2016; HIPE exped.; GenBank: MT251119 , MT251104 ; RMCA 2016.035.P.0164 to 2016.035.P.0165 (Supplementary file SM.01: HP575, HP579) • 1 spec.; Mahoma River , Rwimi-Nyabani road; 0°21ʹ00.2ʺ N, 30°16ʹ41.0ʺ E; 1 Apr. 2017; HIPE exped.; GenBank: MT251110 ; RMCA 2017.006.P.0244 (Supplementary file SM.01: HP1878) • 1 spec.; Lake George, Kashaka Bay , south of inlet; 0°05ʹ04.6ʺ S, 30°10ʹ45.6ʺ E; 2 Feb. 2018; HIPE exped.; GenBank: MT251111 ; RMCA 2018.008.P.0248 (Supplementary file SM.01: HP3246) – Kazinga Channel • 4 specs; Kyambura River , mouth, Kazinga Channel ; 0°07ʹ25.8ʺ S, 30°03ʹ07.5ʺ E; 30 Oct. 2016; HIPE exped.; GenBank: MT251100 , MT251101 , MT251102 , MT251103 ; RMCA 2016.035.P.0155 to 2016.035.P.0158 (Supplementary file SM.01: HP562(2), HP563 to HP565) • 7 specs; same locality; 4 Feb. 2018; HIPE exped.; RBINS 25588 to 25594 (Supplementary file SM.01: Fiche-143 to Fiche-149) • 4 specs; same collection data as for preceding; GenBank: MT251099 , MT251112 ; RMCA 2018.008.P.0249 to 2018.008.P.0252 (Supplementary file SM.01: HP3312, HP3314, HP3317, HP3319) • 1 spec.; Kyambura River , middle course, north of Lake Katinda; 0°12ʹ23.7ʺ S, 30°06ʹ24.3ʺ E; 2 Feb. 2018; HIPE exped.; RBINS 25587 (Supplementary file SM.01: Fiche-128) • 5 specs; Kazinga Channel , near Queen Elisabeth Bush Lodge; 0°08ʹ09.6ʺ S, 30°02ʹ27.6ʺ E; 4 Nov. 2016; HIPE exped.; GenBank: MT251123 , MT251124 , MT251125 , MT251108 , MT251109 ; RMCA 2016.035.P.0166 to 2016.035.P.0170 (Supplementary file SM.01: HP719 to HP721, HP723, HP724) • 2 specs; Kazinga Channel , opposite of mouth Kyambura River; 0°07ʹ17.5ʺ S, 30°02ʹ59.0ʺ E; 4 Feb. 2018; HIPE exped.; RBINS 25595 to 25596 (Supplementary file SM.01: Fiche-121, Fiche-123) .

Description

Based on the lectotype and one paralectotype of E. alberti , the type series of E. cercops , which is synonymised here as E. alberti , and 37 additional specimens from the Lake Edward system, identified as E. alberti . The lectotype is illustrated in Fig. 7a . Maximum observed size: 74.3 mm SL. Morphometric and meristic data are given in Table 2. Body fusiform, largest depth anterior to dorsal fin. Dorsal profile from tip of snout to origin of dorsal fin slightly convex, slightly tapering to base of caudal fin. Ventral profile from operculum to origin of pelvic fin slightly convex, slightly tapering to posterior end of anal fin base, then slightly concave to caudal fin. Head small. Eye large and round, located dorso-laterally, closer to tip of snout than to distal margin of operculum, interorbital profile slightly convex. Snout rounded and mouth subterminal. Two pairs of barbels, anterior barbel usually slightly shorter than posterior with anterior one usually reaching up to vertical through posterior margin of eye, while posterior one usually up to vertical trough posterior margin of pre-operculum. Dorsal fin with 3 unbranched and 7 to 9 branched rays, distal margin straight to slightly concave, origin located slightly anterior [1 or 2 lateral line scale(s)] to vertical through pelvic fin insertion. First branched dorsal fin ray longest, posterior rays decreasing progressively in size. Pectoral fin with 1 unbranched and 13 to 16 branched rays, distal profile straight to slightly convex, not reaching anterior base of pelvic fin. Pelvic fin with 1 unbranched and 6 to 8 branched rays, distal margin slightly convex. Anal fin with 3 unbranched and 5 to 6 branched fin rays, distal margin slightly concave. Caudal fin forked with outer rays twice as long as median ones and both lobes rounded and of similar size. Anus and urogenital opening situated immediately in front of anal fin base. Scales cycloid, rounded and radially striate. Lateral line completely pored with many lateral line scales [27–34 (median 31)], and gently curved downwards over abdomen but running straight along middle of caudal peduncle and ending at base of caudal fin. Lateral-line scales smaller on caudal peduncle than below dorsal fin.

Colour pattern

No sexual dimorphism observed. In life, overall background colour of body silvery, darker toward dorsum and lighter towards belly ( Fig. 7b ). Thick yellowish midlateral band, often with one to three darker spots. All fins translucent. In preserved specimens, overall background colour of body yellowish, greyish dorsally ( Fig. 7a ). One to three dark spots on flanks on thick silvery midlateral band; spots fused into mid-lateral line in some specimens, overlying silvery band and starting posterior to operculum. First spot situated anterior to dorsal fin origin, median one below last ray of dorsal fin and last one at caudal fin base. Specimens with more than three spots are rare (1 specimen with 4 spots and another with 6 spots).

Distribution ( Fig. 10 )

Enteromius alberti occurs in river systems throughout the Lake Edward basin. For the Congolese part of the basin, it is known from its type locality, the Rutshuru River, May-Ya-Moto (Poll 1939). Although the Congolese part of the system was not sampled during the recent expeditions, we identified specimens from the collection at the RMCA (86-01-P-479 to 500 and 86-09-P-70 to 71) from Vitshumbi, located in the southern Congolese part of the Lake Edward system, as E. alberti . In the Ugandan part, we collected the species in the Mahoma, Mpanga, Nchwera, Nyamweru and Kyambura (an affluent of the Rusangwe) Rivers, in Lake Edward offshore at Kayanja, and in Lake George at Kashaka Bay. For the Lake Victoria basin, E. alberti is known from the Nzoia River, the Malawa River and the Middle Akagera system ( Whitehead 1960; Greenwood 1966; De Vos & Thys van den Audenaerde 1990; Seegers et al. 2003).

Figures

Fig. 7. (a) Lectotype of Enteromius alberti (Poll, 1939) (MRAC 64723) with 74.3 mm SL. (b) Fresh specimen of E. alberti (RMCA 2018.008.P.0248 HP 3246) with 62.4 mm SL.

Fig. 3. Scatterplots of (a) interorbital width (IOW), (b) pre-pelvic distance (PrPelD), (c) body depth (BD), (d) maximum caudal peduncle depth (MxCPD), (e) minimum caudal peduncle depth (MnCPD), (f) head width (HW), and (g) head depth (HD) in % SL against SL (in mm) on 72 specimens of Enteromius Cope, 1867. The genetic groups A (●) (n = 22) and B (■) (n = 50) are indicated separately. The dashed lines indicate the size class used for the MWU tests.

Fig. 10. Overview of the sample locations of E. alberti (Poll. 1939) (●) and E. cf. mimus (Boulenger, 1912) (■), including the specimens from Tshambi, in the Lake Edward system. The location of the lectotype and the paralectotypes of E. alberti (♦). The approximate location of the lectotype and the paralectotypes of E. mimus (Boulenger, 1912) (▼) and the holotype and paratypes of E. cercops (Whitehead, 1960) (▲) are indicated in the inset.