1. Ecomorphological Comparison of the Two Cyprinid Fishes Varicorhinus barbatulus and Candidia barbatus in Hapen Creek of the Northern Taiwan Ling-Chuan Chuang 1, 2, *, Shih-Hsiung 3 Liang, and Yao-Sung Lin 1, 2 To study habitat uses and their association with body forms of freshwater fishes, we investigated the distribution of two common and sympatric cyprinid species, Varicorhinus barbatulus and Candidia barbatus, in Hapen Creek from August 1996 to December 1998. A total of 2089 V. barbatulus (1292 in riffles and 797 in pools), and 2759 C. barbatus (923 in riffles and 1836 in pools) were collected. Simultaneously, habitat variables associated with each sampling site, including flow width, water depth, velocity, substrate composition, instream cover and canopy, were measured. Stepwise multiple regressions were used to determine the association of microhabitat characteristics with fish densities. For each fish species, the habitat use was further linked to various morphological indexes stemming from its body form. Results showed that C. barbatus, with a deep, laterally compressed body and larger pectoral fins, preferred habitats in pools; by contrast, V. barbatulus, with a more cylindrical body shape and smaller pectoral fins, did not discriminate habitats in favor of pools or riffles. These findings cope well with the predictions based on assumptions of morphological adaptations of freshwater fishes inhabiting different habitats. In other words, body forms of freshwater fishes could be useful predictors of their habitat preferences and would provide valuable implications for habitat management and ecological engineering on streams. This study was conducted in Hapen Creek, a headwater tributary of the Tanshui River at elevations of 500 m to 1,200 m, where V. barbatulus and C. barbatus were abundant and sympatric. The fish fauna was V. barbatulus, C. barbatus, Crossostoma lacustre, Rhinogobius candidianus, Cobitis sinensis, and Acrossocheilus paradoxus. Three study sites, S1, S2, and S3, were selected, each with four habitat units: two pools and two riffles. Differences in habitat conditions between riffles and pools Fish densities The difference in density of V. barbatulus between habitat types based on paired t-test was not significant (t=0.083, p=0.934), but the density of C. barbatus was significantly higher in pools (t=4.108, p<0.001). Morphological traits of the fishes Relationships of fish densities to hydrological and habitat variables V. barbatulus Sqr (density) = 6.332 – 1.535 Sqr (width) – 2.611 Sqr (depth) (r 2 = 0.389, df = 173) C. barbatus Sqr (density) = 6.774 – 2.113 Sqr (velocity) – 1.953 Sqr (width) – 0.279 Sqr (large boulder) + 0.333 Sqr (canopy) – 0.165 Sqr (cobble) (r 2 = 0.541, df = 170) 1 Department of Life Science, College of Life Science, National Taiwan University. 2 Institute of Ecology and Evolutionary Biology, College of Life Science, National Taiwan University. 3 Institute of Life Science, National Kaohsiung Normal University. * Correspondence: E-mail: lcjaung@ntu.edu.tw.