Embryonic and larval development of the Pacific saury Cololabis saira: Distinctive characteristics of a rapidly...

Pacific saury Cololabis saira is one of the important food resources drawing attention for its recent rapid decline of catch. Their life cycle and embryonic development have been largely unknown. It is important to clarify how the habitat and reproduction of this species have been affected by the global changes of the aquatic environment.

We obtained fertilized eggs of C. saira by spontaneous spawning and artificial fertilization and observed the embryonic development up to larval stages. Embryonic stages are documented with major periods of developmental events: cleavage, gastrulation (epiboly), and somitogenesis and organogenesis. Remarkably, segmentation of somites starts in the middle of epiboly, unlike other well-documented teleost species such as zebrafish and medaka. Morphological changes in the larval stage up to feeding juvenile are also described. Growth speed of larval Pacific saury is dramatically rapid in comparison to closely related beloniform fish such as medaka.

In comparison to medaka, early embryogenesis of saury proceeds relatively slowly, but is followed by an earlier onset of somitogenesis, revealing a distinct developmental timetable. Despite reaching adult body length exceeding 20 cm in only half a year, the developmental basis of the remarkable growth of saury remains unclear. The developmental staging framework established here provides a foundation for future studies investigating the molecular mechanisms underlying saury development, as well as the effects of environmental factors, including ocean warming, on embryonic development and early life-history traits.