SOX5 and Infertility: Notably, clasp2, cracr2a and sox5 were identified as the marker genes for spermatocyte (c1), middle round spermatid (c6), and early round spermatid (c4) respectively in zebrafish testis (Supplementary Table S3), which indicates that zebrafish could be used as a model to study the genes that are associated with human infertility and might help to reveal the underlying mechanism.