Enteromius gamo, Englmaier & Chai & Wubie & Collins & Getahun, 2024

Englmaier, Gernot K., Chai, Min, Wubie, Alemayehu, Collins, Rupert A. & Getahun, Abebe, 2024, A new species within the Enteromius kerstenii complex (Actinopterygii, Cyprinidae, Smiliogastrinae) from south-western Ethiopia, Zootaxa 5512 (2), pp. 166-184 : 172-180

Enteromius gamo sp. nov.

urn:lsid:zoobank.org:act:9686B7D0-FA40-4C78-A33B-4FC44F35E391

Figure 4

Material examined. Holotype ( Figure 4b ). ZNHM 0080 , holotype, 40.0 mm SL, irrigation channel in the floodplain of the Lower Hare River (6°3’35’’N, 37°36’2’’E; 1,185 m a.s.l.), Lake Abaya basin, South Ethiopia Regional State, Ethiopia, 22.11.2023, coll. G.K. Englmaier and A. Wubie, GenBank accessions PP960556 ( COI) and PP965674 (cytb).

Paratypes. ZNHM 0081 , 12 , 30.8–44.7 mm SL, same date and locality as holotype . ZNHM 0082 , 3 , 35.9–37.9 mm SL, same date and locality as holotype, GenBank accessions PP960557–PP960559 ( COI) and PP965675– PP965677 (cytb) . ZNHM 0085 , 4 , 21.7–39.3 mm SL, irrigation channel connected to the Lower Sile River (5°53’31’’N, 37°29’44’’E; 1,122 m a.s.l.), Lake Chamo basin, South Ethiopia Regional State, Ethiopia, 19.11.2023, coll. G.K. Englmaier and A. Wubie. ZNHM 0084 , 1 , 34.1 mm SL, same locality as ZNHM 0085, 20.11.2023, coll. G.K. Englmaier and A. Wubie. ZNHM 0083 , 3 , 28.7–36.5 mm SL, same date and locality as ZNHM 0085, GenBank accessions PP960553–PP960555 ( COI) and PP965671–PP965673 (cytb) .

Diagnosis. Enteromius gamo sp. nov. belongs to a phenotypic group characterised by a thickened and serrated last unbranched dorsal fin ray, a low number of scales in the lateral series (≤ 27), and a yellow, orange or reddish blotch on operculum. The new species is distinguished from E. kerstenii and all examined congeners from Tanzania, Kenya, and Uganda primarily by short anterior (15.8–35.1 % of snout length, not reaching anterior margin of the eye) and posterior (63.2–95.7 % of snout length, extending between the middle of the eye and the posterior margin of the eye) barbels. It further differs by a short predorsal length, 49.6–56.3 % of SL; short pelvic-fin length, 16.9– 20.7 % of SL, not reaching to anal-fin origin; short pectoral-fin length, 17.4–21.2 % of SL, not reaching to pelvic-fin origin; few, 14–15, branched pectoral-fin rays; few, 11, circumpeduncular scales, and few, 10–19 serrae on posterior margin of last unbranched dorsal fin ray.

Description. General appearance of E. gamo sp. nov. shown in Figure 4 , and relative measurements, meristic counts, and coded characters of the holotype and paratypes are given in Table 2 and Supplementary material: Table S3.

Longest examined specimen 44.7 mm SL (ZNHM 0081). Body moderately compressed. Dorsal head profile and predorsal back straight or slightly concave. Postdorsal back outline slightly convex to end of caudal peduncle. Head usually shorter than body depth at pelvic-fin origin. Snout rounded; its length usually slightly greater than horizontal eye diameter. Mouth terminal, tip of mouth cleft slightly lower than level of middle of eye, mouth cleft straight. Anterior barbel short (15.8–35.1 % of snout length) not reaching anterior margin of the eye (coded length 1). Posterior barbel 63.2–95.7 % of snout length, extending between the middle of the eye and the posterior margin of the eye (coded length 3), never reaching beyond posterior margin of the eye. Eye large, but horizontal diameter usually smaller than snout length. Eye diameter relative to snout length negatively correlated with SL (R = -0.80 Spearman’s rank correlation, N = 24). Interorbital width greater than horizontal eye diameter.

Dorsal fin with three unbranched and eight branched rays. Last unbranched ray thickened and densely serrated on posterior margin. Serration extending over 60–72 % (mean 65 %) of non-segmented part, lower non-serrated part relatively short. Number of serrae ranging from 10 (28.7 mm SL) to 19 (44.7 mm SL), but not positively correlated with size (R = 0.44, Spearman’s rank correlation, N = 19). Dorsal-fin origin usually behind origin of pelvic fin. Dorsal-fin depth usually slightly longer than head length. Anal fin with three unbranched and six branched rays, reaching to about middle of caudal peduncle; depth 81.0–102.7 % of caudal-peduncle length. Pelvic fin with one unbranched and seven branched rays, not reaching to anal-fin origin. Pectoral fin with one unbranched and 14 or 15 branched rays, not reaching pelvic-fin origin. Pectoral and anal fins of about similar length, pelvic fin commonly shorter. Caudal fin forked with typically 2+17 principal rays (nine in upper lobe and eight in lower lobe). Upper procurrent rays eight or nine, lower procurrent rays seven or eight ( Table 2 ).

Lateral line complete and downwardly curved below midline, running along midline on caudal peduncle. Total number of scales in the lateral series 25–27, mode 26. Scale rows between lateral line and dorsal-fin origin five, three scale rows between lateral line and pelvic-fin base as well as between lateral line and anus. Circumpeduncular scale rows 11. Back, belly and chest fully scaled. Axillary scale present at pelvic-fin base; length 23.4–44.1 % of pelvic-fin length.

Total vertebrae 32–34, commonly 33; with 17–19 abdominal vertebrae and 15–16 caudal vertebrae; predorsal abdominal vertebrae 8–10, mode 10, other vertebral counts given in Table 2 . Supraneurals five or six (N = 6), first two or three roundish and three or four in front of dorsal fin deeper and elongated.

Gill rakers in outer row of first gill arch 43–45 (N = 3), with 28 or 29 on lower limb and 14, 15, or 17 on upper limb.

In three examined specimens (39.3–41.9 mm SL), length of digestive tract (straightened but not stretched) about 78–81 % of SL. Intestine folded in simple loop before reaching anus.

Mature spawning capable females with large ovaries, i.e. the developing phase of the reproductive cycle ( Brown-Peterson et al. 2011), were observed end of rainy season at sizes of 39.3–41.9 mm SL (N = 3).

Colouration. In life ( Figure 4a ), body silvery or cream-coloured, darker above lateral line with black or brownish back. Blueish, yellowish or orange iridescent above lateral line in anterior half of body, on operculum, and upper eye. Yellow or orange blotch on operculum. Small, distinct black spot at posterior margin of caudal peduncle. Fins pale, base of caudal fin cream-coloured or yellowish.

In formalin (initial fixation) and later transferred to 75 % ethanol specimens ( Figure 4b ), pale cream-coloured. Upper head ash-grey. Back with greyish or black stripe. Faint greyish stripe between anal-fin insertion and caudal fin. Narrow black mid-lateral stripe, most prominent between level of pelvic-fin origin and level of anal-fin insertion, terminating in a small black spot at posterior margin of caudal peduncle. Scales above mid-lateral stripe with abundant, small, and uniformly distributed dark pigments. Concentration of dark pigments at anterior border of pored scales forming chevrons, most distinct anterior to dorsal-fin origin. Small dark brown or black blotch on operculum. Fins white.

Ethanol-preserved specimens ( Figure 4c ), overall cream-coloured and greyish above lateral line, with darker back, and with observable shine at midline and operculum. Narrow black mid-lateral stripe and faint greyish stripe between anal-fin insertion and caudal fin present. Pigmentation of scales similar to specimens initially preserved in formalin, but darker and more intense. Small black spot at posterior margin of caudal peduncle. Fins pale or greyish.

Distribution and habitat. Enteromius gamo sp. nov. is endemic to Ethiopia where it is known only from the endorheic basins of lakes Abaya and Chamo in the SMER. The new species was collected at the end of the rainy season from irrigation channels connected to the lower Sile and Hare rivers with their associated floodplains ( Figure 5 ). In both sampling sites, E. gamo sp. nov. was found sympatric with Enteromius cf. stigmatopygus . Substrate composition was dominated by silt and sand. The altitude of the sampling sites ranged from 1,122 m a.s.l. (5°53’31’’N, 37°29’44’’E) to 1,185 m a.s.l. (6°3’35’’N, 37°36’2’’E). Enteromius gamo sp. nov. was absent from mainstem rivers and only a single specimen was previously found in littoral habitats of Lake Abaya ( Golubtsov et al. 2002). Additionally, the new species was reported from the Sago River, Lake Chamo basin ( Golubtsov et al. 2002).

Gut contents examined (N = 3) contained unidentifiable fine organic detritus, remains of aquatic ( Chironomidae, Ephemeroptera ) and terrestrial ( Formicidae ) arthropods, and some non-organic material (sand grains).

Etymology. The specific epithet gamo was selected in honour of the Gamo people, who inhabit the region around Lake Abaya where the holotype was collected. A noun.

Remarks. The restricted distribution range of E. gamo sp. nov. coupled with environmental pressures from agricultural intensification and subsequent modification of the natural habitat suggest that the new species should be listed with an IUCN (2012) status of Endangered or Critically Endangered.

Comparison of Enteromius gamo sp. nov. with East African congeners. Besides the main diagnostic characters mentioned above, the newly described species from Ethiopia differs clearly from type specimens of E. kerstenii ( Figure 6a , Table 2 ) by 14–15, mode 14, branched pectoral fin rays (vs. 15–16); 25–27, mode 26, scales in the lateral series (vs. 24–25); length of penultimate unbranched dorsal fin ray 26.4–38.3 %, mean 32.2 %, of non-segmented length of last unbranched dorsal fin ray (vs. 37.9–51.7 %, mean 43.1 %, of non-segmented length of last unbranched dorsal fin ray); axillary scale 23.4–44.1 %, mean 31.0 %, of pelvic-fin length (vs. 21.8–25.2 %, mean 23.8 %, of pelvic-fin length); and interorbital width 117.9–169.6 %, mean 143.1 %, of snout length (vs. 114.0–120.3 %, mean 116.4 %, of snout length).

Enteromius gamo sp. nov. is distinguished from the holotype of E. lumiensis ( Figure 6b ), originating from the Lumi River, a tributary to Lake Jipe on the east side of Mount Kilimanjaro (north-eastern Tanzania), by 14–15, mode 14, branched pectoral fin rays (vs. 15); horizontal eye diameter 83.3–117.4 %, mean 97.9 %, of snout length (vs. 82.4 % of snout length); and minimum caudal-peduncle depth 58.3–72.7 %, mean 64.8 %, of caudal-peduncle length (vs. 61.1 % of caudal-peduncle length).

No type material of E. nigrolinea , originating from the Pangani River (historically referred to as “Rufu River” in its middle course), was examined and we refer to published data (original description by Pfeffer 1889) for comparison. Enteromius gamo sp. nov. is distinguished from E. nigrolinea by body depth greater than head length (vs. equal); eye diameter shorter than snout length (vs. longer); and interorbital width considerably shorter than twice eye diameter (vs. almost equal to twice eye diameter). The new species also differs from the holotype of E. salmo ( Figure 6c ), described from the Pangani River, by 10–19, mode 15, serrae on last unbranched dorsal fin ray (vs. 35); and horizontal eye diameter 83.8–117.4 %, mean 97.9 %, of snout length (vs. 77.4 % of snout length). Additional material from the Pangani River drainage ( Figure 7a ), showed that E. gamo sp. nov. differs by length of non-segmented and serrated part of last unbranched dorsal fin ray 59.7–71.5 %, mean 64.7 %, of non-segmented length of last unbranched dorsal fin ray (vs. 66.3–77.5 %, mean 71.4 %, of non-segmented length of last unbranched dorsal fin ray). Data from COI and cytb place specimens from the Pangani River within a group of specimens from other coastal drainages in Tanzania and Kenya, divergent from E. gamo sp. nov. by 7.5–7.8 % (COI) and 9.2–9.4 % (cytb).

We did not examine type material of E. akeleyi , but examination of specimens from the Athi River drainage ( Figure 7b ), closest to the type locality of E. akeleyi , showed that they are different from E. gamo sp. nov. by 3–4, mode 4, unbranched dorsal fin rays (vs. 3); 8–10, mode 9, vertebrae between first pterygiophores of dorsal and anal fins (vs. 7–9, mode 8); and preanal length 71.0–76.7 %, mean 74.4 %, of SL (vs. 68.3–73.0 %, mean 70.9 %, of SL).

Enteromius gamo sp. nov. is further distinguished from E. minchini (Lake Victoria, Figure 6d ) by 8–10, mode 10, predorsal abdominal vertebrae (vs. 9); and minimal caudal-peduncle depth 58.3–72.7 %, mean 64.8 %, of caudal-peduncle length (vs. 56.3–61.4 %, mean 58.8 %, of caudal-peduncle length). Specimens from Lake Bunyoni ( Figure 7c ) in the Upper White Nile are geographically closest to the type locality of E. minchini and distinct from E. gamo sp. nov. by 32–33, mode 32, total vertebrae (vs. 32–34, mode 33); head depth at nape 72.0–81.4 %, mean 75.4 %, of head length (vs. 67.0–74.5 %, mean 71.4 %, of head length); and body depth at pelvic-fin origin 31.0–36.5 %, mean 33.8 %, of SL (vs. 24.8–32.9 %, mean 29.9 %, of SL).

The new species is further distinguished from E. kerstenii -like fishes from south-eastern Tanzania (Rufiji River system) ( Figure 7d ) by 8–10, mode 10, predorsal abdominal vertebrae (vs. 9–10, mode 9); and length of penultimate unbranched dorsal fin ray 26.4–38.3 %, mean 32.2 %, of non-segmented length of last unbranched dorsal fin ray (vs. 34.2–43.0 %, mean 38.6 %, of non-segmented length of last unbranched dorsal fin ray). The number of lateral series scales largely overlaps (25–27 vs. 26–30), but the highest counts of 28–30, recorded in specimens from Rufiji, were not found in E. gamo sp. nov.

Figures

FIGURE 4. General appearance of Enteromius gamo sp. nov. from the lower Sile and Hare rivers; a live specimen, ZNHM 0082, paratype, 36.7 mm SL; b ZNHM 0080, holotype, 40.0 mm SL; c ZNHM 0083, paratype, 36.5 mm SL.

FIGURE 5. Habitat of Enteromius gamo sp. nov. in the lower Sile and Hare rivers; a irrigation channel and associated wetland in the floodplain of the Lower Hare River (6°3’35’’N, 37°36’2’’E; 1,185 m a.s.l.), Lake Abaya basin, type locality of E. gamo sp. nov.; b irrigation channel connected to the Lower Sile River (5°53’31’’N, 37°29’44’’E; 1,122 m a.s.l.), Lake Chamo basin.

FIGURE 6. General appearance of a ZMB 6818, Enteromius kerstenii, lectotype, 62.8 mm SL, “Auf dem Wege von der Zanzibarküste nach dem Kilimandjàro” (Peters 1868: p. 601), Tanzania, photograph: E. Assel; b BMNH 1902.11.8.21, E. lumiensis, holotype, 59.2 mm SL, Lumi River, eastern side of Kilimanjaro, running into Lake Jipi, Tanzania, photograph: © The Trustees of the Natural History Museum, London; c ZMB 13163, E. salmo, holotype, 70.9 mm SL, Pangani River, Tanzania, photograph: E. Assel; d BMNH 1906.5.30.123-124, E. minchini, syntype, 63.9 mm SL, Entebbe, Lake Victoria, Uganda, photograph: © The Trustees of the Natural History Museum, London.

FIGURE 7. General appearance of Enteromius kerstenii from Kenya, Tanzania, and Uganda; a BNMH 1975.10.7.19–31, E. kerstenii, 47.9 mm SL, Upper Pangani River, Tanzania; b E. kerstenii, 75.7 mm SL, Makindu & Tsavo Rivers, Athi River system, Kenya; c BMNH 1958.4.23.1–13, E. kerstenii, 56.8 mm SL, Lake Bunyoni, Uganda; d BNMH 1969.2.11.255–260, E. kerstenii, 36.7 mm SL, Kikwawira, tributary of Kilombero River, Rufiji River system, Tanzania. Photographs: © The Trustees of the Natural History Museum, London.