The gilthead sea bream (Sparus aurata L.) is a marine fish of great importance for fisheries and aquaculture. It has also a peculiar sex-determination system, being a protandrous hermaphrodite. Here we report the construction of a first-generation genetic linkage map for S. aurata, based on 204 microsatellite markers. Twenty-six linkage groups (LG) were found. The total map length was 1241.9 cM. The ratio between sex-specific map lengths was 1:1.2 (male:female). Comparison with a preliminary radiation hybrid (RH) map reveals a good concordance, as all markers located in a single LG are located in a single RH group, except for Ad-25 and CId-31. Comparison with the Tetraodon nigroviridis genome revealed a considerable number of evolutionary conserved regions (ECRs) between the two species. The mean size of ECRs was 182 bp (sequence identity 60-90%). Forty-one ECRs have a known chromosomal location in the pufferfish genome. Despite the limited number of anchoring points, significant syntenic relationships were found. The linkage map presented here provides a robust comparative framework for QTL analysis in S. aurata and is a step toward the identification of genetic loci involved both in the determination of economically important traits and in the individual timing of sex reversal. T HE gilthead sea bream (Sparus aurata L.) is a marine teleost fish that belongs to the family Sparidae. This family contains .100 species, which are divided into two large clades (groups A and B) according to the most recent molecular data (Orrell and Carpenter 2004). Sparids (porgies or sea breams) are demersal fish commonly found in temperate and tropical waters, with a maximum of diversity in the northeast Atlantic and the Mediterranean region (Bauchot and Hureau 1986), and they represent a key element of the coastal marine ecosystem. Sparids are also of great importance for fisheries and aquaculture, being excellent food fish, with high commercial value. S. aurata is the most prominent, with an average cultured production of 100 million metric tons per year. The great importance of the gilthead sea bream for marine aquaculture has fueled an increasing number of studies in many different areas such as immunology, endocrinology, bone morphology, and muscle physiology. Moreover, the genomic tool kit for S. aurata has been constantly improving, as a firstgeneration cDNA microarray was recently reported (Sarropoulou et al. 2005), a preliminary radiation hybrid (RH) map has been constructed (Senger et al. 2006), and a medium-scale expressed sequence tag (EST) sequencing project has been recently completed (A. Canario, personal communication). An improved RH map with .1000 markers (G. Kotoulas, personal communication) and an oligo array representing .10,000 unique transcripts (L. Bargelloni, personal communication) are expected by the end of 2006. Therefore, the genome of the gilthead sea bream is rapidly becoming one of the best characterized among teleost species, apart from classical models such as Brachydanio rerio (zebrafish...

Recently the genomes of two more teleost species have been released: the medaka (Oryzias latipes), and the three-spined stickleback (Gasterosteus aculateus). The rapid developments in genomics of fish species paved the way to new and valuable research in comparative genetics and genomics. With the accumulation of information in model species, the genetic and genomic characterization of nonmodel, but economically important species, is now feasible. Furthermore, comparison of low coverage gene maps of aquacultured fish species against fully sequenced fish species will enhance the efficiency of candidate genes identification projected for quantitative trait loci (QTL) scans for traits of commercial interest. This study shows the syntenic relationship between the genomes of six different teleost species, including three fully sequenced model species: Tetraodon nigroviridis, Oryzias latipes, Gasterosteus aculateus, and three marine species of commercial and evolutionary interest: Sparus aurata, Dicentrarchus labrax, Oreochromis spp. All three commercial fish species belong to the order Perciformes, which is the richest in number of species (approximately 10,000) but poor in terms of available genomic information and tools. Syntenic relationships were established by using 800 EST and microsatellites sequences successfully mapped on the RH map of seabream. Comparison to the stickleback genome produced most positive BLAT hits (58%) followed by medaka (32%) and Tetraodon (30%). Thus, stickleback was used as the major stepping stone to compare seabass and tilapia to seabream. In addition to the significance for the aquaculture industry, this approach can encompass important ecological and evolutionary implications.

No abstract

Six new microsatellite loci were isolated and characterized in 32 individuals from a farm population of gilthead seabream (Sparus aurata). Expected heterozygosity at all loci was high, ranging from 0.835 to 0.958 with between 10 and 27 alleles per locus. A multiplex polymerase chain reaction protocol was developed using four of the loci. Cross‐species amplification of the loci was tested in six species of the Sparidae family and four loci were successfully amplified in two or more related species.

No abstract