Embryonic and larval development of the Pacific saury Cololabis saira: Distinctive characteristics of a rapidly growing beloniform fish

BackgroundPacific 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 aquatic environment. ResultsWe 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 larval stage up to feeding juvenile is also described. Growth speed of larval Pacific saury is dramatically rapid, in comparison to closely related beloniform fish such as medaka. ConclusionsIn comparison to medaka, early embryogenesis of saury proceeds slowly, although being followed by early onset of somitogenesis. This might be partly responsible for the rapid growth into adult (larger than 20 cm in body length) in only half a year. Further studies on embryonic development will uncover the molecular mechanisms underlying the characteristics of Pacific saury as an excellent source of nutrition and as an indicator of major environmental changes such as global warming.