Chydorus ventricosus Daday 1898

48. Chydorus ventricosus Daday, 1898 Localities and specimens found: 17 – 2♀; 26 – 2♀, 1♀ ov, 1♀ em, 6j. Distribution and ecology. According to the latest ideas, Ch. ventricosus s. str. is distributed only in the Oriental biogeographic realm (Rajapaksa & Fernando 1986a; Kotov et al. 2013b; Sinev & Korovchinsky 2013; Sinev et al. 2015). This is a well-known but in patches uncommon member of the genus in the region (Chiang & Du 1979; Idris 1983; Michael & Sharma 1988; Sanoamuang 1998; Tanaka & Ohtaka 2010; Chatterjee et al. 2013; Korovchinsky 2013; Kotov et al. 2013b; Van Damme et al. 2013; Ji et al. 2015; Sinev et al. 2015; Lopez et al. 2017; Sharma & Sharma 2017; Tiang-nga et al. 2020; Choedchim & Maiphae 2023). In Vietnam, the species has so far been recorded in several locations in the central and southern provinces (Sinev & Korovchinsky 2013; present study). Chydorus ventricosus is a littoral species occurring in a wide range of water bodies and habitats, generally nonrunning (Idris 1983; Rajapaksa & Fernando 1986a; Michael & Sharma 1988; Sanoamuang 1998; Van Damme et al. 2013; Sinev et al. 2015; Choedchim & Maiphae 2023). We found some of its individuals in the coastal area of a natural lake and reservoir (see Appendix 1). Remarks. Outside the Oriental area, the Ch. ventricosus -like populations should be revised as they most likely belong to other close relatives, including those not-yet-described (Rajapaksa & Fernando 1986a; Chatterjee et al. 2013; Kotov et al. 2013b; Van Damme et al. 2013). In addition, in the past, Ch. ventricosus was apparently often confused with other sibling species (e.g., Ch. reticulatus, Ch. sphaericus, Ch. pubescens, etc.) (Michael & Hann 1979; Frey 1982c; Rajapaksa & Fernando 1986a). Thus, the actual distribution of the species still needs to be clarified.