Enteromius gamo Englmaier, Chai, Wubie, Collins & Getahun, 2024, sp. nov.

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. ......continued on the next page ......continued on the next page ......continued on the next page 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 (v