To explore the function of the gene in spleen development, we generated a knockout zebrafish line. To investigate whether the phenotypic consequences in the seahorses were caused by a missense mutation in this gene, we generated a point mutation zebrafish line by CRISPR/Cas9-mediated homologous recombination (HR). RNA-seq of these samples tissues (brain, liver, kidney, and intestine) were analyzed. In addition, to clarify the splenic phenotype of the Syngnathidaes, the transcriptomic profiles of the S. biaculeatus spleens and the H. erectus small white organ were also sampled and sequenced.