## 1 Introduction  
Sex determination has received significant research attention in various animals, and numerous genes involved in sex determination have been found in many model species (human, mice, goat, chicken, zebra fish, killifish and cichlid), including _sox9_, _foxl2_, _wnt4_ and _dmrt1_[1, 2, 3]. Facilitated by high conservation, sex-related genes in other species have been identified through homology screening [4, 5]. However, the sex-determination mechanisms in fish (especially teleost fishes) are not as well conserved as those in mammals or birds [6, 7]. Fishes are extremely diverse in the sex chromosome systems and exhibit a variety of sex-determining systems among vertebrates, resulting in many reproductive strategies [8, 9]. Therefore, it is important to screen differentially expressed genes (DEGs) in different sexes and enhance our understanding of sexual differentiation in fishes. Furthermore, growth is often related to gender. Sexual growth dimorphism could be observed in many teleost fish, and these species often show different growth rates between the genders [10,11]. Fish growth is a complex polygenic trait. It is regulated by numerous factors, including the nutrients, energy metabolism, environment and reproductive activity [12]. Thus, elucidating the sex differentiation in fish could help us understand the behavioral, cellular and phenotypic differences between sexes in vertebrates [13].  
The lizardfish, _Saurida elongata_ ([PERSON], 1846), is a commercially important teleost species that distributes in subtropical and tropical seas of the northwest Pacific, ranging from the coastal waters of Japan to the northern South China Sea (SCS) [14,15]. Lizardfish is primarily used to produce various fish gel products (fish cakes or surimi) due to its high gel-forming ability and meat yield [16]. In addition, it has been reported that lizardfish can be the basic raw material of biologically active peptide production for the treatment of hypertension, heart failure and other cardiovascular disease [17,18]. The lizardfish is abundant, and it has been reported that the production of lizard fish is estimated at more than 120,000 tons in Guangxi of China [17]. As an economic fishery species, there are many studies on the stock resources [19], biology [15], food chemistry [18] and population genetics [20] of _S. elongata_. However, the biogeochemical and molecular studies on _S. elongata_ are insufficient due to limited gene sequence information, as only a few sequences were encountered during searches of public domain nucleotide and protein databases. Moreover, genomic studies on lizardfish are lacking, as these species are difficult to rear. There were only nine records in the SRA (Sequence Read Archive) database of NCBI.  
Recently, with rapid advances in next-generation sequencing (NGS) technologies, RNA sequencing has emerged as a useful tool for transcriptome analysis enrichment [9,21]. This technique is ideal for identifying candidate genes and pathways underlying the traits of species whose genome is not yet available [22,23]. Recently, numerous studies have successfully used this approach for genes, single-nucleotide polymorphism (SNP) and simple sequence repeat (SSR) discovery in numerous teleost fishes, such as turbid (_Scophthalmus maximus_) [24], silver silago (_Sillaso silama_) [25] and crimson seabream (_Paragyrops edita_) [26], among others. Despite the economic importance of lizardfish (Synodontidae), no published genome or transcriptome sequence is currently available for these species. In the present study, the first transcriptome of different tissues (muscle, gonad, liver and heart) in male and female _S. elongata_ was reported. We focused on genes related to sex differentiation of _S. elongata_. In addition, we also screened numerous simple sequence repeats (SSRs) loci in the transcriptome of _S. elongata_ and developed the SSRs markers. The present study provided valuable genomic information of lizardfish and will facilitate further molecular biology research in teleost.