Body length and weight relationships were estimated for sixteen native freshwater fish species (ten Characidae, three Loricariidae, two Heptapteridae and one Astroblepidae, mainly small-sized fish) collected in the Andean piedmont Hacha River (Caquetá, Colombia) by electrofishing. These are the first length–weight and length–length parameters reported for the species, which are mostly endemic to the Amazonian basin. Maximum lengths in eight of the sixteen studied species are also reported. Knowledge of this biometric data and their relationships can be relevant in the management and conservation of the local fish and fisheries.