Fish Fauna and Community Structure of Gaecheon Stream

This study investigated the fish fauna, tolerance and trophic guild characteristics, and community structure in Gaecheon Stream, a tributary of the Yeongsan River system, based on two surveys conducted in spring and autumn of 2021. A total of 15,294 individuals belonging to 40 species, 11 families, and five orders were collected near 31 weirs. The assemblage included one endangered species, <i>Liobagrus obesus</i> (endangered wildlife class I), two invasive alien species (<i>Lepomis macrochirus</i> and <i>Micropterus salmoides</i>), and 13 species endemic to the Korean Peninsula. The dominant species was <i>Zacco platypus</i> (38.7%), followed by <i>Zacco temminckii</i> (16.6%). Tolerance guild analysis revealed that intermediate species were most abundant from downstream to midstream sections (S1-S25), whereas the proportion of sensitive species increased toward the upstream areas (S26-S31). Only sensitive species occurred at site S31. Trophic guild analysis indicated that insectivores (43.98%) and omnivores (52.70%) dominated the assemblages, while carnivores accounted for 3.32%. Community indices were as follows: diversity 2.32, richness 4.05, evenness 0.63, and dominance 0.55. Bray-Curtis similarity analysis (69.6%) classified the survey sites into four groups: downstream (A), mid-downstream (B), upstream (C), and headwater (D). These findings provide essential baseline information for understanding spatial patterns in fish assemblages associated with weir installation and offer valuable insights for the conservation and ecological management of aquatic ecosystems within the Yeongsan River system.