Comparative Genomics Analysis Provides Insights into Pregnancy Maintenance Mechanisms in the Ovoviviparous Teleost Black Rockfish (Sebastes schlegelii).

The black rockfish (Sebastes schlegelii), an economically important ovoviviparous teleost in Chinese aquaculture, exhibits a distinctive reproductive strategy characterized by internal fertilization and prolonged embryonic development within females until live birth. However, this reproductive mode poses substantial challenges in artificial breeding practices due to a poor understanding of pregnancy (hereafter referring to intraovarian gestation in S. schlegelii) maintenance mechanisms. Here, we conducted a comparative genomic analysis between S. schlegelii and representative oviparous and ovoviviparous fishes, identifying 374 lineage-specific gene families associated with cellular signaling, metabolic regulation, immune response, and developmental processes. In addition, 73 gene families with significant expansions were identified to be mainly involved in extracellular matrix (ECM) structure and regulation, and neuromodulation. Furthermore, 164 genes potentially associated with mitochondrial function, metabolic pathways and angiogenesis were subjected to strong positive selection. Notably, expression profiles of candidate functional genes associated with ECM structure and regulation, and angiogenesis were detected using transcriptomic data of stage V ovary, optic vesicle stage, and pigmentation stage for ovarian stroma tissue, highlighting the vital roles of ECM remodeling and angiogenesis during pregnancy. These findings provide novel insights into the molecular mechanisms underlying pregnancy maintenance in S. schlegelii and contribute to a broader understanding of the genetic adaptations with pregnancy in ovoviviparous teleosts.