In Japan, we have developed a hatching and
release business that takes advantage of the salmon's tendency to return to
their mother rivers and obtains them as highly productive fishery resources. We
aim to upgrade this business to a more robust and sustainable food production
system that can adapt to ecosystem considerations and climate change, and
through our research we hope to contribute to the SDGs (Zero Hunger, Enriching
The United Nations has designated the decade
beginning in 2021 as “the Decade of Marine Science” to contribute to the SDGs.
Marine science as defined by the UN includes the field of fisheries.
Dorsal and ventral fins are near the center of the body.
Let's look at other fish species.
ニシン: Pacific herring 真鯛: Red sea bream 市場魚貝類介類図鑑HPより: Pictures from the Market Fish and Shellfish Catalogue website
Pacific herrings, like salmonids, have dorsal and
ventral fins near the center of their bodies, but red sea breams are different.
Fins without conspicuous hard thorns (spines), consists mainly of soft striae only.
Pictures from the Market Fish and Shellfish Catalogue website
The dorsal fin of sea bream has spiny rays.
The role of these spines is thought to be to protect them from enemies.
Why, then, do sea breams have spiny rays
but salmon do not?
Let us consider the differences in life
history and habitat.
We will also examine the development of
spiny rays in other fish species and consider the similarities and differences
Axillary process (axillary scales) at the base of the ventral fin
Chum salmon (Oncorhynchus keta)
Rainbow smelts, the family Osmeridae, have
an adipose fin but no axially scales.
Rainbow smelt (Osmerus mordax)
Parr mark (pattern resembling a pebble) on the body of juvenile
Parr marks are spots on the body of
juvenile fish during their river life.
They are thought to be for camouflage as
they resemble pebbles on the river bottom.
Conversely, when spending time at sea,
salmonids undergo a morphological change called smoltification, in which their
backs turn gray and their bellies turn white.
This is thought to be due to a
countershading effect, whereby they assimilate the color of the seafloor when
viewed from above and the color of the sky when viewed from below, making them
harder to spot by predators.