Seasonal variations in and effect of incubation water temperature on vertebral number in naturally spawning chum salmon Oncorhynchus keta

Seasonal variations and reaction norms for vertebral number ( V N ) in response to incubation water temperature were estimated in adult and juvenile naturally spawning chum salmon Oncorhynchus keta . The mean V N of adults varied according to spawning time; the early-spawning population had higher V N values than the late-spawning population. Moreover, the mean V N values in the early-spawning population decreased with seasonal changes, whereas V N values in the late-spawning population remained stable. Chum salmon embryos in three full-sib families were incubated at five different temperatures until hatching, and the V N values of the resulting juveniles were analyzed. The V N reaction norm to incubation water temperature showed a V-shaped curve that was lowest at an intermediate temperature. The mean V N at the same incubation temperature varied among the three families. These results suggest that V N values in chum salmon are influenced by genetic components and incubation water temperatures. V N may be a useful parameter for estimating the environmental conditions during ontogenesis and the genetic background by detecting population changes.