Identification of sex-linked marker and candidate sex determination gene in ornamental fish, African scat (Scatophagus tetracanthus)

Abstract

The aquarium industry greatly threatens biological diversity via biological invasion. Mono-sex culturing is an important technique to reduce the possible biological invasion introduced by the aquarium fish, which escape into their non-native environment. African scat (Scatophagus tetracanthus) is a valuable aquarium fish species worldwide. Herein, its sex-linked marker and candidate sex determination (SD) gene were identified through genome sequencing. The whole genome of the male African scat was sequenced using the next-generation sequencing technology. The assembled genome is 630.96 Mb with a scaffold N50 of 38,217 bp. Phylogenetic analysis revealed that African scat diverged from spotted scat (S. argus) approximately 10.5 million years ago. One sex-linked marker (Marker-1) was detected in African scat. Marker-1 amplified a single band of 873 bp in female African scat, and double bands of 873 bp and specific 772 bp in male African scat. Next, Marker-1 was validated in 60 cultured African scat with 100% consistency. Sequence analysis revealed that the 873 and 772 bp fragments were both Dmrt1 homologous sequences. These results imply that the African scat possesses the XY sex-determination system (XX females, XY males), with Dmrt1 as its sex-linked gene. Dmrt1 cDNA sequences on the X and Y chromosomes were also cloned and labeled as Dmrt1∆X and Dmrt1Y, respectively. The amino acid (aa) sequences coded by Dmrt1∆X and Dmrt1Y were 143 aa and 300 aa, respectively. Dmrt1Y mRNA was specifically expressed in the testis, with no expression in the ovary. Therefore, Dmrt1Y is male-specific and a candidate SD gene. The genome data and sex-linked marker of African scat will be helpful for its commercial management to prevent its biological invasion. Besides, the identification of its candidate SD gene contributes to the basic research of SD in vertebrates.