Conservation Genomics of Natural and Translocated Populations of the Swan galaxias ( Galaxias fontanus ), an Endangered Tasmanian Freshwater Fish

This is the authors' abstract. We don't add key points for this paper.

Genomic analyses of endangered species persisting in fragmented populations reveal how genetic diversity is distributed, clarifying historical connectivity and providing insight into each population's adaptive potential. They also directly inform management actions such as conservation translocations. The Swan galaxias ( Galaxias fontanus ) is a stream‐dwelling fish restricted to a few headwater tributaries in two river catchments in Tasmania, Australia, and is the focus of conservation management, including translocations. We used ddRAD sequencing to characterise genetic diversity across the seven core G. fontanus populations (three natural and four translocated), measuring SNP variation against a 612‐Mb contig‐level genome assembly generated using PacBio HiFi long‐read sequencing. All populations were genetically distinct, indicating limited historical connectivity, and the strongest divergence occurred between catchments. Nucleotide diversity was twice as high in the two natural Macquarie River catchment populations compared with the single remaining natural Swan River catchment population. Translocated populations maintained diversity comparable to their source populations, although allele frequency shifts were evident, consistent with genetic drift in both groups over the 30 years since translocation. The Dukes River translocation population preserves genetic variation from the main branch of the upper Swan River where fish have since been extirpated. There was no evidence of hybridisation with G. brevipinnis at Cygnet River, a translocation site where the two species have come into contact. These genomic data have directly guided the design and implementation of two new mixed‐source translocations and provide a foundation for ongoing conservation management of G. fontanus .