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Grafton, Australia

Nock C.J.,Southern Cross University of Australia | Ovenden J.R.,Molecular Fisheries Laboratory | Butler G.L.,Grafton Aquaculture Center | Wooden I.,Narrandera Fisheries Center | And 2 more authors.
Journal of Fish Biology | Year: 2011

Microsatellite markers were used to examine spatio-temporal genetic variation in the endangered eastern freshwater cod Maccullochella ikei in the Clarence River system, eastern Australia. High levels of population structure were detected. A model-based clustering analysis of multilocus genotypes identified four populations that were highly differentiated by F-statistics (FST = 0· 09 - 0· 49; P < 0· 05), suggesting fragmentation and restricted dispersal particularly among upstream sites. Hatchery breeding programmes were used to re-establish locally extirpated populations and to supplement remnant populations. Bayesian and frequency-based analyses of hatchery fingerling samples provided evidence for population admixture in the hatchery, with the majority of parental stock sourced from distinct upstream sites. Comparison between historical and contemporary wild-caught samples showed a significant loss of heterozygosity (21%) and allelic richness (24%) in the Mann and Nymboida Rivers since the commencement of stocking. Fragmentation may have been a causative factor; however, temporal shifts in allele frequencies suggest swamping with hatchery-produced M. ikei has contributed to the genetic decline in the largest wild population. This study demonstrates the importance of using information on genetic variation and population structure in the management of breeding and stocking programmes, particularly for threatened species. © 2011 The Authors. Journal of Fish Biology © 2011 The Fisheries Society of the British Isles.

Foley D.A.,Grafton Aquaculture Center | Foley D.A.,University of New England of Australia | Rowland S.J.,Grafton Aquaculture Center | Wilson G.G.,University of New England of Australia | And 3 more authors.
Aquaculture Research | Year: 2010

Slow growth and losses to bird predation and infectious diseases in winter can compromise the profitability of silver perch farming. To evaluate over-wintering silver perch (Bidyanus bidyanus) in a recirculating aquaculture system (RAS), fingerlings (38 g) were stocked in either cages in a pond at ambient temperatures (10-21 °C) or tanks in the RAS at elevated temperatures (19-25 °C) and cultured for 125 days. Mean survival (96%), final weight (146 g), specific growth rate (1.07%day-1) and production rate (28.1kgm-3) of fish in the RAS were significantly higher than for fish over-wintered in cages (77%, 73 g, 0.53%day-1, 11.1kgm-3). Fish from both treatments were then reared in cages for a further 129 days. Final mean weight of fish originally over-wintered in the RAS was 426 g, while fish over-wintered in cages were only 273 g. To determine optimal stocking densities, fingerlings (11.8 g) were stocked at 500, 1000 or 1500 fish m-3 in tanks in the RAS and cultured for 124 days. Survival was not affected, but growth was significantly slower and feed conversion ratio higher at 1500 fish m-3 compared with 500 or 1000 fish m-3. Results demonstrate that over-wintering silver perch in an RAS can produce large fingerlings for grow-out in early spring. This strategy could eliminate bird predation, reduce losses to diseases and shorten the overall culture period. © 2009 Blackwell Publishing Ltd.

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