adult males and females gammarus pulex ( size average : 10  mm and 7  mm , respectively ) were collected in the blanc - gravier ( 503460n and 53460e , lige , belgium ) , a stream of good physicochemical quality , as defined by the european directive , and in the vesdre river ( 503600n and 53758e , vaux - sous - chevremont , belgium ) which is a river contaminated by several organic micropollutants ( e.g. pcb dioxine - like and nondioxin like , benzo(a)pyrene ) . after transferring the samples to the laboratory into the corresponding river water , each individual were dissected to sample the hepatopancreas tissue . in order to have a wide range of conditions in the analysed sample , and increase the probability of protein detection , 5 hepatopancreas of males and 5 hepatopancreas of females , coming from the uncontaminated site , and 5 hepatopancreas of males and 5 hepatopancreas of females , coming from the contaminated site , were pooled ( i.e. 10 hepatopancreas males and 10 hepatopancreas of females per pool ) . indeed , some proteins could be expressed ( or over - expressed ) only in contaminated conditions , as well as differently according to gender ; thus , a mixture of uncontaminated / contaminated individuals and males / females allow to increase the probability of identifying more transcripts . pooled samples were performed in duplicates , total rna were immediately isolated using a qiagen rneasy lipid tissue minikit ( qiagen , germany ) , following the manufacturer 's instructions . truseq rna libraries were synthesised and sequenced using 2    100 base paired - end ( illumina hiseq 2500 , genoscreen , lille , france ) , and mixs descriptors are presented in table 1 . the sequencing allowed to produce an average of 290.8  m of paired - end reads of which 85.6% were of good quality ( q30 score ) . all the sequences were then taken into further process of redundancy removing using cd - hit - est v4.6   with a sequence identity threshold of 90% , leaving 39,801 sequences corresponding to 10,878 potential genes ( table 2 ) . the assembled transcriptome was annotated using blatp v2.2.29 with an e - value threshold of 1    10 . assembled contigs were deposited in the european nucleotide archive under the bioproject number prjeb13055 , with accession numbers fjvi01000001-fjvi01039801 ( http://www.ebi.ac.uk/ena/data/view/prjeb13055 ) . adult males and females gammarus pulex ( size average : 10  mm and 7  mm , respectively ) were collected in the blanc - gravier ( 503460n and 53460e , lige , belgium ) , a stream of good physicochemical quality , as defined by the european directive , and in the vesdre river ( 503600n and 53758e , vaux - sous - chevremont , belgium ) which is a river contaminated by several organic micropollutants ( e.g. pcb dioxine - like and nondioxin like , benzo(a)pyrene ) . after transferring the samples to the laboratory into the corresponding river water , each individual were dissected to sample the hepatopancreas tissue . in order to have a wide range of conditions in the analysed sample , and increase the probability of protein detection , 5 hepatopancreas of males and 5 hepatopancreas of females , coming from the uncontaminated site , and 5 hepatopancreas of males and 5 hepatopancreas of females , coming from the contaminated site , were pooled ( i.e. 10 hepatopancreas males and 10 hepatopancreas of females per pool ) . indeed , some proteins could be expressed ( or over - expressed ) only in contaminated conditions , as well as differently according to gender ; thus , a mixture of uncontaminated / contaminated individuals and males / females allow to increase the probability of identifying more transcripts . pooled samples were performed in duplicates , total rna were immediately isolated using a qiagen rneasy lipid tissue minikit ( qiagen , germany ) , following the manufacturer 's instructions . truseq rna libraries were synthesised and sequenced using 2    100 base paired - end ( illumina hiseq 2500 , genoscreen , lille , france ) , and mixs descriptors are presented in table 1 . the sequencing allowed to produce an average of 290.8  m of paired - end reads of which 85.6% were of good quality ( q30 score ) . all the sequences were then taken into further process of redundancy removing using cd - hit - est v4.6   with a sequence identity threshold of 90% , leaving 39,801 sequences corresponding to 10,878 potential genes ( table 2 ) . the assembled transcriptome was annotated using blatp v2.2.29 with an e - value threshold of 1    10 . assembled contigs were deposited in the european nucleotide archive under the bioproject number prjeb13055 , with accession numbers fjvi01000001-fjvi01039801 ( http://www.ebi.ac.uk/ena/data/view/prjeb13055 ) .
so far , ecotoxicological studies used biomarkers of exposure or of effects in order to investigate the impacts of contaminated areas on biota ( peakall , 1994 [ 6 ] ) . 
 however , although these results are important in the ecotoxicological risk assessment , biomarkers are very specific and only provide information on the biological processes or physiological pathways targeted by the biomarkers experimenters choose to test ( monsinjon and knigge , 2007 [ 5 ] ) . in recent years , proteomics have become a major tool in ecotoxicology , as they provide a global insight into the mechanism of action of pollutants without the need of hypothesis testing or any preconception on the biological processes likely impacted ( gismondi et al . , 2015 ; trapp et al . , 2015 [ 7 ] ; 
 truebano , 2016 [ 8 ] ) . however , the analysis of proteomic results is often limited due to the lack of database , especially for non - model organisms , such as gammarus sp , commonly used as biological model in ecotoxicology ( sornom et al . , 2012 [ 11 ] ; vellinger et al . , 
 2013 [ 9 ] ; gismondi and thom , 2014 [ 1 ] ; lebrun et al . , 2014 
 [ 3 ] ) . here , we performed illumina hiseq sequencing to total rna isolated from the hepatopancreas ( i.e. detoxification tissue ) of gammarus pulex males and females coming from uncontaminated river and contaminated river ( e.g. pcb , benzo(a)pyrene ) . 
 approximately 290  m paired - end reads were assembled , filtered and sorted into 39,801 contigs whose 10.878 were similar of proteins available in databases . 
 the assembled contigs could represent a reference hepatopancreas transcriptome for g. pulex , and constitute an important resource for future investigations on the impacts of pollutants on invertebrate biota , since it would improve the understanding of the mechanisms of action involved in toxicity . 
 in addition , the hepatopancreas transcriptome will also allow the identification of new potential biomarkers for the ecotoxicological risk assessments . 
 assembled contigs were deposited in the european nucleotide archive under the bioproject number prjeb13055 , with accession numbers fjvi01000001-fjvi01039801 .