Enteromius mimus ( Boulenger, 1912 )

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 : 18-21

Enteromius mimus ( Boulenger, 1912)

Fig. 8 , Table 2

Diagnosis

Enteromius mimus ( Fig. 8 ) 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 to 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 mimus can easily be distinguished from the other species of this group from the East Coast and Nilo-Sudan ichthyofaunal regions by the following combinations of characteristics (data from original description, unless otherwise stated): a complete lateral line vs an incomplete lateral line in E. atkinsoni , E. pumilus , E. serengetiensis , E. tongaensis and E. toppini ; two pairs of barbels vs one pair in E. pseudotoppini , and no barbels in E. anema and E. profundus ; 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 and E. yongei , and a thin dark line from the beginning of the operculum to the caudal fin base in E. viviparus ; 11–12 scales around the caudal peduncle vs 8 in E. leonensis , 9–10 in E. venustus , and 10 in E. magdalenae and E. yeiensis ; 24–27 lateral line scales (median 25) vs 30 in E. lineomaculatus , and 31 E. innocens ; 3.5–4.5 scales between the dorsal fin base and the lateral line vs 5.5 in E. unitaeniatus , and 6 in E. usambarae ; 3–4 scales between the lateral line and the pelvic fin (median 3) vs 2 in E. trispilopleura , and 2–2.5 in E. neglectus ( Boulenger 1907) ; 7–8 branched dorsal fin rays vs 9 in E. quadripunctatus ; a body depth which is larger than the head length vs a body depth which is equal to the head length in E. nigeriensis ; a smaller snout length [4.1–7.1% SL (average 6.0) vs 7.1–10.1] in E. radiatus ( Greenwood 1970) . Enteromius mimus differs from E. perince by a combination of a lower number of lateral line scales [24–27 (median 25) vs 29–30 (30)], a lower number of scales between the dorsal fin base and lateral line [3.5–4.5 (median 3.5) vs 5.5], a lower number of scales around the caudal peduncle [11–12 (median 12) vs 14], a smaller interorbital width [6.3–8.3% SL (average 7.8) vs 9.8–10.2 (10.0)], a larger pre-pectoral distance [26.0–29.0% SL (average 27.4) vs 23.1–24.5 (23.8)], a lower minimum caudal peduncle depth [11.1–14.0% SL (average 12.5) vs 15.0–16.4 (15.5)], a lower maximum caudal peduncle depth [12.9–16.5% SL (average 14.6) vs 17.7–19.4 (18.8)], and a smaller anal fin base length [7.3–8.7% SL (average 8.0) vs 8.5–9.6 (9.1)]. Enteromius mimus differs from E. stigmatopygus by a combination of a smaller pre-pectoral distance [26.0–29.0 (average 27.4) vs 29.1–33.1 (30.8)], and a larger anal fin length [18.0–19.7 (average 19.0) vs 12.6–17.4 (14.8)]. Enteromius mimus differs from E. alberti by a lower number of lateral line scales [24–27 (median 25) vs 27–34 (31)], a larger pre-anal distance [68.4–74.8% SL (average 72.4) vs 65.1– 73.0 (69.3)], a smaller post-anal distance [16.3–19.3% SL (average 17.8) vs 16.3–24.2 (21.1)], a larger body depth [26.5–34.3% SL (average 30.1) vs 21.7–31.2 (26.9)], a larger head depth [17.8–21.8% SL (average 20.2) vs 15.1–19.0 (17.3)] and a larger pelvic fin length [18.2–22.4% SL (average 20.4) vs 15.0–20.9 (18.0)] ( Table 2). Specimens from E. mimus differ from the specimens of the population of E. cf. mimus from the Lake Edward system by a lower number of scales between the origin of the dorsal fin and the lateral line [3.5–4.5 (median 3.5) vs 3.5–4.5 (4.5)], a larger pelvic fin length [18.2–22.4% SL (average 20.4) vs 14.4–21.3 (18.5)], a smaller snout length [4.1–7.1% SL (average 6.0) vs 4.6–8.3 (7.0)], a smaller interorbital width [6.3–8.3% SL (average 7.8) vs 6.9–9.9 (8.7)], a larger post-dorsal distance [34.8–40.4% SL (average 38.1) vs 31.0–39.9 (35.9)] and a larger anal fin length [18.0–19.7% SL (average 19.0) vs 14.4–21.8 (17.7)] ( Table 2).

Etymology

The specific epithet ‘ mimus ’ means ‘imitator’, a reference to the ‘striking resemblance’ to E. neglectus ( Boulenger 1912; Scharpf & Lazara 2019).

Material examined

Lectotype (here designated)

KENYA • Euasso Nyiro , bellow falls, British EastAfrica; BMNH1912.3.22.99 (Supplementary file SM.01: Fiche-185).

Paralectotypes

KENYA • 8 specs [of 9 in lot]; same collection data as for lectotype; BMNH 1912.3.22.90 to 1912.3.22.98 (Supplementary file SM.01: Fiche-184, Fiche-186 to Fiche-188, Fiche-B to Fiche-E) .

Description

The redescription of E. mimus is based on the specimens of the type series only (the lectotype and eight paralectotypes).The lectotype is illustrated in Fig. 8 . Maximum observed size: 45.6 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 laterally, closer to tip of snout than distal margin of operculum, interorbital profile slightly convex. Snout rounded. Mouth subterminal. Two pairs of barbels, anterior barbel shorter than posterior with anterior one usually reaching up to vertical through the middle of the eye, while posterior one can reach the vertical trough posterior margin of pre-operculum. Dorsal fin with 3 unbranched and 7 to 8 branched rays, distal margin slightly concave, origin located on vertical through pelvic fin insertion or slightly anterior (1 lateral line scale). First branched dorsal fin ray longest, posterior rays decreasing progressively in size. Pectoral fin with 1 unbranched and 12 to 14 branched rays, distal profile straight to slightly convex, not reaching anterior base of pelvic fin. Pelvic fin with 1 unbranched and 7 branched rays, distal margin convex. Anal fin with 3 unbranched and 5 to 6 branched fin rays, distal margin 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 (total) [24–27 (median 25)], gently curved downwards over abdomen but running straight along middle of caudal peduncle and ending at base of caudal fin.

Colour pattern

No sexual dimorphism is observed. No information of in vivo colour pattern is available. In preserved specimens, overall background colour of body brown, darker dorsally. 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 or somewhat anterior to last ray of dorsal fin and last one at caudal fin base.

Distribution

Enteromius mimus is known from its type locality, the Euasso Nyiro River below the falls, east of Lake Baringo, Kenya, and from the Tana River system ( Seegers et al. 2003). For the time being, the specimens of the Lake Edward system are referred to as E. cf. mimus and are not included in the distribution of E. mimus .

Figures

Fig. 8. Lectotype of Enteromius mimus (Boulenger, 1912) (BMNH 1912.3.22.99) with 43.6 mm SL.