This study represents the first large-scale population genetic analysis of the marine fish gilthead sea bream (Sparus aurata), one of the most significant species in the South European aquaculture. Six wild and five cultivated sample sets covering the South Atlantic and Mediterranean European area have been screened for allozyme, microsatellite and mitochondrial DNA (mtDNA) variation. Microsatellites showed higher levels of polymorphism than allozymes. The low variability of mtDNA offered no basis for population differentiation.
The results reveal levels of variability for S. aurata above those from other sparids sparids. Cultivated populations show a slight decrease of variability related to the wild ones, but not sufficient to document inbreeding depression effects, thus suggesting a fairly proper management. Wild populations reveal a slight degree of differentiation more pronounced with microsatellites than with allozymes, but not apparently associated with geographic or oceanographic factors. The cultivated populations seem to be highly divergent as a result of genetic drift caused by different factors pertaining to their respective histories. With both markers, the two cultivated Spanish sample sets are the most divergent. The high differentiation between cultivated and wild populations from the same area might indicate no evidence for significant genetic flow between them.
This study provides an insight into the population structure of S. aurata, although more questions have arisen that need to be solved. This can be achieved by further screening of small-scaled targeted sample sets in the studied area.
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