| Diagnosis: |
Dorsal spines (total): 0-0; Dorsal soft rays (total): 11-12; Anal spines: 0-0; Anal soft rays: 9-9; Vertebrae: 33-34. Diagnosis: Enteromius yardiensis belongs to a phenotypic group characterised by small size and the last unbranched dorsal-fin ray thickened and serrated (Ref. 121538). It is readily distinguished from its Ethiopian congeners by three unique specialisations: the absence of the anterior barbel, the absence of the medial branch of the supraorbital cephalic canal and few, 1-3, commonly 2, scale rows between lateral line and anus (Ref. 121538). It further differs by posterior barbel usually shorter than half eye diameter; eye large, its diameter 24-34% of head length; snout short and pointed; lateral line complete and strongly curved; scales in the lateral series 32-35; few transversal scale rows between lateral line and pelvic-fin base, 1-3; scale rows between dorsal- and pelvic-fin origins 7-10; often four unbranched dorsal-fin rays; few branched pectoral-fin rays, commonly 12 or 13; 17-18 abdominal vertebrae; 10-12 predorsal abdominal vertebrae; and 6-9 vertebrae between first pterygiophores of dorsal and anal fins (Ref. 121538).
Description: Body markedly compressed; dorsal head profile slightly concave, its transition to back smooth, slight nuchal hump only present in few larger individuals; head commonly longer than body depth at pelvic-fin origin (Ref. 121538). In most specimens, predorsal back outline steeply rising to dorsal-fin origin; post-dorsal back outline slightly convex or straight to end of caudal peduncle; head depth at nape not exceeding head length; snout pointed and relatively short, its length not exceeding eye horizontal diameter; mouth terminal, tip of mouth cleft on about level of middle of eye, mouth cleft straight; posterior barbel short, shorter than half eye diameter; anterior barbel absent in all specimens but foramen for its nerve present in maxillary; eye large, its horizontal diameter greater than snout length but shorter than lower jaw length; eye diameter negatively correlated with standard length; interorbital width is commonly less than eye horizontal diameter (Ref. 121538). Dorsal fin with three or four unbranched and eight branched rays; last unbranched ray moderately thickened and densely serrated; serration extending over more than 76% of ray non-segmented part, and lower non-serrated part relatively short and not strongly thickened; number of serrae ranging from 10 to 27 and positively correlated with size; in case of four unbranched rays, first ray often small and only visible in radiographs; predorsal body long and dorsal-fin origin placed behind origin of pelvic fin; dorsal-fin depth slightly shorter than head length; anal fin with three unbranched and six branched rays, reaching to about middle of caudal peduncle; pelvic fin with one unbranched and commonly seven branched rays, commonly reaching behind anus and rarely to anal-fin origin; pelvic splint variable in length but relatively short, 19-32% of pelvic-fin length; pectoral fin with one unbranched and commonly 12-13 branched rays, commonly not reaching pelvic-fin origin; pectoral, pelvic and anal fins of about similar length; caudal fin forked with 2+17 principal rays, commonly eight in upper lobe and seven in ower lobe; upper procurrent rays 7-9, lower procurrent rays 6-8 (Ref. 121538). Lateral line complete and clearly downwardly curved on the body going along midline on posterior half of caudal peduncle; total lateral series with 32-35, commonly 33, scales; circumpeduncular scale rows 12-14; back, belly and chest fully scaled; short axillary scale present at pelvic-fin base (Ref. 121538). Five infraorbital bones but fourth often fragmented into two; third to fifth infraorbital bone wide, covering most surface of cheek in front of preoperculum; fifth infraorbital bone as wide as deep or wider as deep (Ref. 121538). Supraorbital canal complete lacking medial branch of supraorbital canal in all specimens; infraorbital and supratemporal canals complete; preoperculo-mandibular canal complete between lower jaw and preoperculum and not communicating with postocular commisure of infraorbital canal; preopercular section of this canal terminating at pper margin of preoperculum or continuing into suprapreopercular segment fused to antedorsal process of operculum terminating by free pore over its upper margin or somewhat below (Ref. 121538). Total vertebrae few, 33-34; supraneurals 5-6, first three or four square-shaped and two or three in front of dorsal fin deeper and elongated (Ref. 121538). Gill rakers in outer row of first gill arch 10-12, with eight or nine on lower limb and two on upper limb; pharyngeal teeth thin and slightly hooked, not serrated, 2.3.5-5.3.2 (Ref. 121538).
Colouration: In life, overall silvery, with greenish brown back; greenish iridescence especially at nape and upper eye; fins pale, base of pectoral, pelvic and anal fins sometimes faintly pinkish, caudal-fin base brownish; no stripe or blotches (Ref. 121538). Most ethanol-preserved specimens overall silvery with much shine at midline, ventral and opercular regions; other body parts brownish orange or silvery grey; fins pale, base of caudal fin and, often, anterior part of dorsal-fin base ash-grey (Ref. 121538). Formalin and later transferred to 75% ethanol specimens creamy to yellowish, formalin-deposited whitish; back greyish brown, posterior head brownish black; narrow black mid-lateral stripe usually of increasing intensity at caudal peduncle but not reaching caudal-fin base; ventral body, especially bases of pectoral and anal fins, often yellowish; fins pale, anterior part of dorsal-fin base brownish; sparse melanophores on rays of dorsal, caudal and anal fins (Ref. 121538). |
| Biology: |
Found in shallow shoreline habitats of the main channel of Awash River, deep stretches of side channels, stagnant water bodies of the adjacent floodplain, and in the shoreline of the lakes (Ref. 121538). A preference for structured habitats with aquatic plants, woody debris, dense river bank vegetation and fine substrate, sand and finer fractions, was noted; a pronounced difference between wet and dry season is characteristic for the area Ref. 121538). Water is usually turbid and water temperature ranged from 26.1°C to 31.9°C (Ref. 121538). Gut contents contained unidentifiable fine organic detritus and remains of planktonic crustaceans but also nematodes, remains of terrestrial arthropods, diatoms, larger plant material, seeds, and wood debris, and some non-organic material (Ref. 121538). |