Thermal tolerance to high temperature was evaluated in the large yellow croaker Larimichthys crocea. The survival thermal maximum for L. crocea was 33.0°C, the 50% critical thermal maximum(50% CTMax) was 35.5°C, and the critical thermal maximum(CTMax) was 36.0°C. Three microsatellite markers(LYC0148, LYC0200 and LYC0435), associated with thermal tolerance were screened and identified using a Bulked Segregation Analysis(BSA) method. These markers have six amplified fragments in which four are related to thermal tolerance. These fragments were cloned and sequenced, and the results showed the core motif were all "AC" repeats. For LYC0148 and LYC0200, the lengths of fragments are 181 bp and 197 bp, respectively. For LYC0435, which has two fragments, the fragment lengths are 112 bp and 100 bp. The results provide useful molecular markers for thermal-tolerance breeding of large yellow croaker in the near future.
The large yellow croaker,Larimichthys crocea is an important marine fish in China with a high economic value.In the last decade,the stock conservation and aquaculture industry of this species have been facing severe challenges because of wild population collapse and degeneration of important economic traits.However,genes contributing to growth and immunity in L.crocea have not been thoroughly analyzed,and available molecular markers are still not sufficient for genetic resource management and molecular selection.In this work,we sequenced the transcriptome in L.crocea liver tissue with a Roche 454 sequencing platform and assembled the transcriptome into 93 801 transcripts.Of them,38 856 transcripts were successfully annotated in nt,nr,Swiss-Prot,InterPro,COG,GO and KEGG databases.Based on the annotation information,3 165 unigenes related to growth and immunity were identified.Additionally,a total of 6 391 simple sequence repeats(SSRs) were identified from the transcriptome,among which 4 498 SSRs had enough flanking regions to design primers for polymerase chain reactions(PCR).To access the polymorphism of these markers,30 primer pairs were randomly selected for PCR amplification and validation in 30 individuals,and 12 primer pairs(40.0%) exhibited obvious length polymorphisms.This work applied RNA-Seq to assemble and analyze a live transcriptome in L.crocea.With gene annotation and sequence information,genes related to growth and immunity were identified and massive SSR markers were developed,providing valuable genetic resources for future gene functional analysis and selective breeding of L.crocea.
