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. 2016 Oct 27;4:e2593.
doi: 10.7717/peerj.2593. eCollection 2016.

Who's Your Mama? Riverine Hybridisation of Threatened Freshwater Trout Cod and Murray Cod

Free PMC article

Who's Your Mama? Riverine Hybridisation of Threatened Freshwater Trout Cod and Murray Cod

Alan J Couch et al. PeerJ. .
Free PMC article


Rates of hybridization and introgression are increasing dramatically worldwide because of translocations, restocking of organisms and habitat modifications; thus, determining whether hybridization is occuring after reintroducing extirpated congeneric species is commensurately important for conservation. Restocking programs are sometimes criticized because of the genetic consequences of hatchery-bred fish breeding with wild populations. These concerns are important to conservation restocking programs, including those from the Australian freshwater fish family, Percichthyidae. Two of the better known Australian Percichthyidae are the Murray Cod, Maccullochella peelii and Trout Cod, Maccullochella macquariensis which were formerly widespread over the Murray Darling Basin. In much of the Murrumbidgee River, Trout Cod and Murray Cod were sympatric until the late 1970s when Trout Cod were extirpated. Here we use genetic single nucleotide polymorphism (SNP) data together with mitochondrial sequences to examine hybridization and introgression between Murray Cod and Trout Cod in the upper Murrumbidgee River and consider implications for restocking programs. We have confirmed restocked riverine Trout Cod reproducing, but only as inter-specific matings, in the wild. We detected hybrid Trout Cod-Murray Cod in the Upper Murrumbidgee, recording the first hybrid larvae in the wild. Although hybrid larvae, juveniles and adults have been recorded in hatcheries and impoundments, and hybrid adults have been recorded in rivers previously, this is the first time fertile F1 have been recorded in a wild riverine population. The F1 backcrosses with Murray cod have also been found to be fertile. All backcrosses noted were with pure Murray Cod. Such introgression has not been recorded previously in these two species, and the imbalance in hybridization direction may have important implications for restocking programs.

Keywords: Conservation genetics; Freshwater management; Hybridisation; Introgression; Maccullochella; Murray Cod; Murrumbidgee River; Restocking; SNPs; Trout Cod.

Conflict of interest statement

The authors declare there are no competing interests.


Figure 1
Figure 1. Upper Murrumbidgee River Maccullochella hybridisation study area.
Collection sites are shown in larger black text and putative barriers to adult fish migration are shown in smaller red text. Barriers from F Dyer, M Lintermans & P Couch (2014, unpublished data).
Figure 2
Figure 2. Principle Components of Maccullochella snps.
PCA plot of Maccullochella snps from the upper Murrumbidgee River 2011–2013 (n = 278: 251 larvae, 25 adults, two known Trout cod). Trout Cod samples are in light blue on the right, Murray Cod in purple at the origin. The first and second generation hybrids (red and brown respectively) can be seen in between. The two third generation larva (fish #102 and #106) are in green and #106, is partially obscured within the purple Murray cod points. The two points with ♀MC had a Murray Cod as female parent based on their mtDNA. All other hybrids larvae had a Trout Cod as the female parent lineage.

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Grant support

The Australian Government Department of Education and Training and ICON Water (ACT) provided funding for this project as a PhD student scholarship. Additional financial support was provided by Carlton-Mid through Recreational Fishing Research ( The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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