Compliance with Ethical Standards Otolith analysis was funded by a RAC grant from the University of New Mexico, USA. The Government of Chile supported the drafting of this document with a CONICYT Doctoral Fellowship to D. Alò in 2015 and to C. Correa through grants CONICYT-PAI N°82130009, and FONDECYT-Iniciación en la Investigación N°11150990. All applicable international, national, and/or institutional guidelines for the care and use of animals were followed. Specimens were collected under permits No. 3587, 29 December 2006, and No. 2886, 4 November 2008 (amendment No. 602, 12 February 2009) granted by the Chilean Subsecretary of Fishing to C. Correa. The McGill University Animal Care Committee (UACC), Animal Use Protocol No. 5291, approved use and handling of animals. Abstract Coastal habitats in Chile are hypothesized to support a number of diadromous fishes. The objective of this study was to document migratory life histories of native galaxiids and introduced salmonids from a wide latitudinal range in Chilean Patagonia (39-48°S). Otolith microchemistry data were analysed using a recursive partitioning approach to test for diadromy. Based on annular analysis of Sr:Ca ratios, a diadromous life history was detected for populations of native Aplochiton taeniatus, A. marinus , and Galaxias maculatus . Lifetime residency in freshwater was suggested for populations of A. zebra and G. platei . Among introduced salmonids, populations of Oncorhynchus tshawytscha and O. kisutch exhibited anadromous migratory patterns, whereas the population of O. mykiss screened appeared restricted to freshwater. Salmo trutta exhibited variable habitat use consistent with establishment of an ocean-type life history in some populations. The capacity and geographic scope of hydropower development is increasing and may disrupt migratory routes of diadromous fishes. Identification of diadromous species is a critical first step for preventing their loss due to hydropower development.