New insights into Aplochiton species at its southernmost distribution

Abstract

Aplochiton is a small genus of galaxiid fish endemic to southern South America, consisting of three species: A. taeniatus, A. zebra, and A. marinus. Historical data on these species are scarce, and their current distribution is poorly understood, especially in the southernmost parts of their range. In this study, we compiled reliable records of Aplochiton from Argentina and Chile, complemented by new empirical data from extensive freshwater sampling in Tierra del Fuego (TDF). Our results indicate similar distribution patterns for both species: A. zebra ranges from the Biobío River (37.5°S) to Navarino Island (55.1°S), while A. taeniatus is found from the Tirúa River (38.37°S) to the Beagle Channel (55.08°S). Extensive surveys in TDF over 11 years, conducted in 58 rivers using electrofishing, detected Aplochiton in the Azopardo River basin (Pacific drainage) and the Olivia River (Beagle Channel drainage). Molecular phylogenetic analyses validated species identification, revealing a single haplotype of A. zebra in the Azopardo River basin and A. taeniatus in the Olivia River basin. Habitat characterization showed A. zebra occupies river–lake transitional zones, coexisting with exotic salmonids. This study refines the known distribution of Aplochiton, confirms the coexistence of two species in TDF, and provides essential ecological information for conservation.