Ecological differentiation and environmental plasticity in Bagarius: a comparative review across Asian river systems

The genus Bagarius comprises large predatory catfishes distributed across major river systems of South and Southeast Asia, yet ecological information remains uneven among species and is complicated by recent taxonomic revisions. Here, we conducted a comparative literature synthesis of seven currently recognized Bagarius species, integrating information on geographic distribution, habitat use, feeding ecology, reproduction, movements, body size, threats, and conservation status. Historical records attributed to B. yarrelli were retained as a taxonomic reference but were not treated as an additional valid species. The synthesis revealed pronounced ecological differentiation among species despite a recurrent association with large, flowing river environments, including rocky substrates, rapids, strong currents, and structurally complex channels. Differences were also evident in body size, trophic ecology, and movement patterns, with seasonal movements documented particularly well for B. lica. However, species-specific evidence was highly uneven, and information on reproduction, movements, population biology, and fine-scale habitat use remained limited for several taxa, particularly the recently described B. protos and B. dolichonema. Recent taxonomic revisions further demonstrate that historical records attributed to B. yarrelli may represent multiple currently recognized species, constraining direct interpretation of historical ecological and conservation information. The observed ecological breadth is compatible with the Dynamic Environmental Reconfiguration Hypothesis (DERH), but does not constitute direct empirical validation. Overall, Bagarius represents a promising comparative system for investigating ecological plasticity in heterogeneous river environments, while conservation and future ecological research should be conducted at species and drainage-system levels.