As shown above, it is important
to measure the growth of juvenile fish during their movement from the
river to estuary to coast to offshore in order to estimate chum salmon stock recruitment. The most secure way of doing so is to label an
individual fish, recapture it after some time, and observe changes in size.
However, it is extremely difficult to re-capture a fish released into the wild.
Therefore, methods for indirectly measuring the growth of fish are generally
used. The ring patterns in the otoliths and scales record the growth and
habitat of each fish, which is useful for reconstructing past growth history.
Furthermore, the amount of ribosome RNA in the muscles is said to reflect the
degree of protein synthesis, that is, the growth of the muscles and the ratio
per cell (DNA) (RNA/DNA ratio) is used as an index of current or recent growth.
Our research group focuses on the insulin-like growth factor (IGF)-I, a hormone
that controls growth, as a growth index of either current or recent growth.