Fig. 1

a Sri Lanka, showing the geographical origin of samples of Pethia nigrofasciata and P. bandula used in this study. The thin black lines indicate basin boundaries, while the bold black line indicates the 2000-mm isohyet, which encompasses the wet zone. Numbers on the map (a) represent the sampling localities listed in Table 1. b close-up of the sampling localities for P. nigrofasciata in the headwaters of the Attanagalu basin neighboring the type locality of P. bandula. These populations show a mix of meristic characters and color patterns intermediate between P. nigrofasciata and P. bandula. In d–r, specimens with complete and incomplete pored lateral-line scales are represented by black and white squares, respectively while those with complete bar beneath dorsal fin and those without or an incomplete are represented by black and white circles, respectively. Numbers on the map (b) are referenced to the specimens illustrated in (g–n) in parentheses. c Live coloration of P. bandula. d Holotype of P. bandula, ZRC 38,483, 34.6 mm SL, e paratype CMK 7146C, 31.6 mm SL, and f paratype, CMK 7146D, 30.8 mm SL of P. bandula. Pethia cf. nigrofasciata from the Attanagalu basin in g–n. g DZ5353F, 40.3 mm SL (2). h DZ4452C, 38.8 mm SL (5). i DZ4452A, 36.9 mm SL (5). j DZ5352B, 39.0 mm SL (2). k DZ5350E, 42.6 mm SL (4). l DZ5351I, 37.1 mm SL (3). m DZ5350G, 35.7 mm SL (4). n DZ5351A, 34.8 mm SL (3). o Live coloration of P. nigrofasciata. Pethia nigrofasciata in p–r. p DZ4403A, 39.1 mm SL, Kelani basin. q DZ4059B, 32.3 mm SL, Bentara basin. r DZ4509B, 44.2 mm SL, Walawe basin