Materials and methods
Study Sites.  Sampling was done under the framework of the Joint Ethiopian‐Russian Biological Expedition (JERBE) in six rivers draining the Ethiopian Highlands and belonging to its four major river basins (Fig. 2): (1) the White Nile basin – the Birbir R. – 8.7364° N 35.3518° E, and the Sore R. at two locations – at the City of Metu – 8.3178° N, 35.5951° E – and ~35 km downstream along the river course – 8.3987° N, 35.4378° E; (2) the Blue Nile basin – Blue Nile at the City of Dejen – 10.0775° N 38.1934° E – and the Didessa R., a tributary of the Blue Nile – 8.6921° N 36.4144° E; (3) the Omo-Turkana enclosed basin – the Gojeb R., a tributary of the Omo R. – 7.2539° N 36.7943° E; (4) the Juba-Wabe-Shebelle basin in the Indian Ocean catchment – the Genale R. – 5.7025° N 39.5446° E. Fish were caught by gill and cast nets in March 2014 (Birbir), February–March 2011 (Didessa), March–April 2009 (Genale), February 2011 (Gojeb), April 2014 (Sore), and January 2022 (Blue Nile). Fish were killed with an overdose of MS-222 anaesthetic and then photographed using a Canon EOS 50D camera (Canon Inc. Ota City, Tokyo, Japan). Standard length (SL, mm) was measured with a ruler. Fish were preserved first in 10% formalin and then transferred to 70 % ethanol. All specimens are deposited at A.N. Severtsov Institute of Ecology and Evolution, the Russian Academy of Sciences, Moscow under provisional labels of JERBE. In total, up to 296 samples were investigated by a set of various methods (Table 1).
Table 1. Sample size of the generalized and thick-lipped ecomorphs of Labeobarbus for various analyses.