Environmental DNA (eDNA) survey of Tilapia on the mid coast (Geraldton region) of Western Australia

Objective: Tilapia (Oreochromis mossambicus) is an invasive species that is now found in several states of Australia including Queensland, NSW and in Western Australia. The objective of this study was to conduct a survey of tilapia in Western Australia to identify waterbodies where tilapia may occur using environmental DNA (eDNA) as the detection method. Discussion & Recommendations: Based on the eDNA survey results, tilapia DNA was detected and are likely to be present in all waterways surveyed in the W.A. mid coast region. Chapman Spalding Park and Chapman Community Sites had strong detection rates for tilapia confirmed via qPCR and Sanger sequencing analysis. The sequence generated when blasted to the NCBI data base matches existing sequences in Gen Bank. The detection rates for tilapia were low in some sites (i.e. Greenough Devlin Pool, Greenough Ellendale Pool and Chapman Morell Road). This may be due to low levels of tilapia infestation or a sampling effect. Nevertheless all eDNA sanger sequences generated from two of these sites (Greenough Devlin Pool and Chapman Morell Road) were matching 100% tilapia species in the Genbank at NCBI data base.It must be noted that not all quality control measures were entirely followed by DIT staff (EC samples were not included for every sample, rather only the first sample for each site) for this survey. Future surveys need to ensure that an EC is done for each sample and not just for the site so any cross contamination within site samples can be monitored. Despite the EC not been done for each sample the results from this survey strongly suggest a widespread detection of tilapia and the lack of contamination in controls that were included leans to the results being reliable