Sample collection, sex identification
We used samples of 261 Macquarie perch, 68 golden perch, 4 Murray cod
and 4 trout cod (Supplementary Material S1). Of 261 Macquarie perch
individuals, 173 were Snobs Creek hatchery broodstock from the Yarra
River and Lake Dartmouth (see Lutz et al., 2020 for details of the
breeding program), 25 were Narrandera hatchery broodstock from the
Abercrombie River, one was a Snobs Creek hatchery-produced juvenile, and
the remaining 62 were adults sampled from four inland and five coastal
populations. The inland lineage (including Yarra, Dartmouth and
Abercrombie populations) diverged from the coastal one in the
Pleistocene; the two are morphologically distinguishable (Pavlova,
Beheregaray, et al., 2017). Sex was identified for hatchery broodstock
and 21 sampled-and-released fish from inland King Parrot Creek and
Holland’s Creek by observation of mature gametes during the breeding
season. For all but two individuals (exceptions in next section),
fin-clip samples were collected non-lethally and preserved in absolute
ethanol at -20°C.
Of the 68 golden perch from three populations, 66 were sampled lethally
for another project, and their sex identified during dissection based on
presence of maturing or mature gonads. Fin clips from two males and two
females were also used for each of Murray cod and trout cod, with their
sex determined at Snobs Creek hatchery (details of sampling and sexing
in Supplementary Material S1). All procedures employed were approved by
relevant animal care and ethics committees. Field sample collection was
approved by NSW ACEC 14/10, DELWP AEC 14/04 and AEC 15/02, Scientific
Collection Permit P01/0059(A)-3.0 and Victorian Fisheries Research
Permit RP827. Hatchery work and sampling were conducted under approval
of VIC DPI Fish AEC Jul09 0067 and NSW Fisheries ACEC committee 05/06.