Ovenden, J.R., Macbeth, G.M., Pope, L., Thuesen, P., Street, R., and Broderick, D. (2015) Translocation between freshwater catchments has facilitated the spread of tilapia in eastern Australia. Biological Invasions, 17 (2). pp. 637-650.

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Abstract

Understanding dispersal routes of invasive species is essential to their control. Tilapiine fish species are archetypal invaders of freshwater habitats. They were first reported from Australia in the 1970s and have spread rapidly. Incursion into Australia's largest inland catchment, the Murray Darling Basin, may threaten its largely endemic freshwater fauna. Direct (spatial and temporal distribution) and indirect (genetic data from eight microsatellite loci and mitochondrial DNA sequence) information was used to subjectively construct invasion scenarios. Specifically, we tested the expectation that tilapias have been translocated between freshwater catchments presumably as a consequence of their popularity as bait for angling, display in aquariums and for the table. Five cross-catchment translocation events were inferred involving dispersal across distances up to 300 km. Translocation was not rampant, however, as genetic distinctiveness among catchments was observed. Tilapia in eastern Australia had genetic affinities to Oreochromis spirulus, O. hornourum urolepis and O. aureus, beyond their expected affinity to O. mossambicus. Some individuals had admixed genomes suggesting on-going hybridisation between lineages. Other individuals had zero nuclear genetic diversity at eight microsatellite loci demonstrating the tolerance to severe inbreeding. There was evidence of temporal instability in the composition of populations; for example, in an artificial dam in the south (Tingalpa Weir) one genetic lineage appeared to have replaced another over a period of approximately 20 years. Authorities have clear rationale to more strictly enforce regulations that prohibit possession of this species (dead or alive), and a window of opportunity for effective action given that translocation, while occurring, is currently not rife.

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