Page 52 - Fish and Amphibians (Britannica Illustrated Science Library)

48 DIVERSITY FISH AND AMPHIBIANS 49

The Journey Home Survival

Of the more than 7,500 eggs that two females can lay, only two
hatched fish will remain at the end of the life cycle of two years.
fter living in the ocean for five or six years, the Pacific red salmon (Oncorhynchus Many eggs die before hatching, and after hatching, salmon fry are
easy prey for other fish.
nerka) returns to the river where it was born to reproduce. The journey lasts from
A two to three months, and it demands a great deal of energy. The salmon must swim Eggs 7,500
against the current, climb waterfalls, and evade predators, including bears and eagles. Once 2 Red River Fry 4,500
The salmon returns to its
the salmon reach the river, the female lays her eggs, and the male fertilizes them. Typically, birthplace to spawn. Males Fry 650
the same locations in specific rivers are sought year after year. This species of salmon dies have intense coloration Fry 200
with a green head. Salmon 50
after completing the reproductive cycle, unlike the Atlantic salmon, which repeats the cycle Adult 4
three or four times. Once the eggs hatch, the cycle begins anew. Salmon
Egg 2
Spawning

1 Strenuous Race 3 The Couple 5,000
Salmon swim upstream from the
While females are busy preparing nests
ocean to the river. On the way
many fall prey to bears. in the sand to deposit their eggs, males QUANTITY OF EGGS A
compete for mates. FEMALE CAN LAY
Seen from above, salmon
appear as a large red spot.
MOUTH BACK
During mating season, A hump develops in
the lower jaw of the the dorsal section of
6-Year male curves upward. the body.
ASIA ALASKA U.S..
Cycle
The Route LENGTH OF TIME COLOR
The blue-backed
There are six species of salmon in the Pacific FROM SPAWNING salmon turns a
fiery red.
Neither waterfalls nor
Ocean and one in the Atlantic. The red salmon TO ADULTHOOD
(Oncorhynchus nerka) migrates from the strong currents can stop
salmon in their journey.
Pacific Ocean to the rivers of the United
States and Canada on one side and to the
rivers of Alaska and eastern Asia on the other.
5 Fry 4 Spawning
The female deposits between
Only 40 percent of the eggs
2,500 and 5,000 eggs in a series
3 months Death laid each autumn hatch. The of nests. The male fertilizes them
fry remain in the river for
as they fall between the rocks.
migrate to the ocean.
ESTIMATED DURATION OF THE 6 Adult salmon die a few days after up to two years and then
spawning, exhausted by the work
SALMON'S JOURNEY TO THE they have done. Their bodies
RIVER WHERE IT WAS BORN decompose along the river bank.