Transcript Fish Life Cycle - Exploits Valley High

Salmon, Cod and Trout
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Salmon have a most interesting life. One that takes
them from the rivers and streams to the high seas of
the Ocean, and back again. In fact, right back to the
very place they were born. How they find their way
back from the immensity of the Ocean is a small feat
in itself.
Salmon are anadromous fish - they live in the sea but
reproduce in fresh water (in a stream or lake). They
are amazing fish that live in fresh water during their
early life, mature in salt water, and then return to
fresh water to breed (and then die). Some salmon
travel up to 1,600 km upstream in order to spawn.
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Starting out as small eggs in a stream bed, they hatch and begin
their journey downstream towards the ocean. They spend a
couple of years in the streams and rivers growing from small
alevin to juvenile smolts. At the mouth of the streams and rivers,
the smolts school together and ready themselves for the trip out
into the ocean. During this time, their bodies change to adapt to
the seawater. The young adult salmon then head out to sea and
spend several years swimming in the ocean. Once they have fully
matured, they will swim back to their original stream or river
where they re-adapt to the fresh water and swim back up the
stream to reach their spawning grounds. Sometimes this means
swimming up rugged rivers with miles of rapids and even
waterfalls to leap. Once they get back to their natal stream, they
breed and lay their eggs. After spawning they generally die
within a week, fertilizing the stream and creating a nutrient-rich
environment for the new infant salmon that are about to hatch.
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Eggs (Ova)
Salmon are born in gravel nests at the bottom
of stream and river beds in the form of a
slightly translucent eggs about the size of a
pencil eraser. The eggs are usually red to
pink in color and spherical in shape. During
the 2-3 month period it take the eggs to
hatch, their eyes and other organs can be
seen developing through the translucent shell
of the egg.
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When the salmon egg is ready to hatch, the
baby salmon will break free of the egg's soft
shell retaining the yolk as a nutrient-rich sac
that hangs below it's body. At this stage, they
are called Alevin and are about one inch in
length. During the next month, the alevin will
remain hidden in the gravel nest and feed
from the nutrient-rich yolk sac until it is
completely absorbed.
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The tiny salmon leave their gravel nest and
begin to swim and feed for themselves. At
this stage they are called Fry and take the
form of tiny fish. It's also at this time that
they start their journey downstream. The first
part of their journey is a difficult one as the
small vulnerable fry must hide under rocks
and among vegetation to avoid predators
such as birds, insects, and other fish. At the
same time, they must find feed to survive.
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After several months, as the Fry feed and
grow, they develop vertical markings on the
flanks of their bodies. At this stage they are
called Parr and are about six inches in length.
Though a bit bigger they still must hide from
predators and continue their journey towards
the ocean. Parr will continue to feed for 1 to 3
years before they are ready venture out into
the ocean.
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At this point, the juvenile salmon loses its
vertical markings on its body and turns
silvery in color. Now considered Smolt, they
will school together in large groups. It's at
this time that the young salmon will adjust
their bodies to saltwater, allowing them to
swim out into the Ocean to feed and grow
into adult salmon.
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Adult salmon spend 1 to 4 years in the ocean
swimming and feeding. They grow to their adult
size and develop unique adult markings that are
different for all species of salmon. There ocean
journey is long and hazardous, as they are
constantly hunted for by seals, orca whales, and
fishermen. After swimming throughout the Ocean
they return to their original spawning grounds to
spawn. In some cases, young adult salmon return
early before they have fully grown.
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Upon reaching their birth rivers and streams, the adult
salmon re-adapt to the fresh water and begin their
upstream journey to their natal stream where they were
born. At this time, they cease to feed and live on the
stores of fat within their bodies. Their upstream journey is
a challenging one, swimming upstream against rugged
rapids, leaping over rocky waterfalls, traversing fish
ladders, avoiding fishermen nets and hooks, and staying
clear of hungry bears. When they finally reach their natal
stream they have reached sexual maturation and are ready
to spawn. The female adult clears a spot in the streambed
by sweeping her tail back and forth creating a gravel nest
that is referred to as a redd. She will then lay her eggs in
this redd and the male adult salmon will fertilize and
protect them until both salmon die within a couple of
weeks and leave the embryos to fend for themselves.
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Reproduction: Salmon live most of their life in the sea, but when they are mature and ready to breed, they enter
fresh water to spawn (reproduce), traveling to a stream or pond high in oxygen. The female digs a nest in the
gravel (called a redd) with her tail. She then pushes her thousands of eggs into the nest and the male milks the
eggs, fertilizing them. Most salmon die after spawning.
The Eggs Hatch and Grow: The newly-emerged salmon (called alevins) still have a food sac attached to them.
When the food sac is used up, the salmon fry emerges from the nest - and must find food (like insects) for the
first time. As the fry matures, it becomes camouflaged (with parr marks) and is called parr . When it becomes
silver-colored, it will be called a smolt. After growing for a while, the smolts swim downstream to the sea.
Adapting to Salt Water: When smolt reach the estuary (where the river meets the sea), a process begins in which
their body changes, allowing them to soon live in salt water (this is called smoltification).
Maturing at Sea, then Returning Home: The salmon lives in the sea until maturity (1 to 7 years, depending on
the species); some migrate thousands of miles in the sea. They then return to the place where they hatched and
continue the cycle. No one knows how salmon return home -perhaps they remember the distinctive set of smells
along the way. On their journey home, they do not eat at all, they often change color, their muscles soften, and
they will die soon after spawning.
Anatomy: Salmons have silvery skin with spotted back and fins. The biggest salmon is the chinook, which
weighs up to 120 pounds (55 kg).
Diet: Salmon are carnivores (flesh eaters) - they eat fish (like herring and pilchard), squid, and crustaceans (like
shrimp).
Predators: Salmon are preyed upon by many animals, including bears, people, many birds (like wading birds and
kingfishers), and other fish. For every 8000 eggs produced, 4500 alevin survive, from which 650 fry survive,
from which 200 parr survive, from which 50 smolt survive, from which only 2 spawning adults survive (who
produce thousands of eggs).
Classification: Kingdom Animalia, Phylum Chordata, Class Osteichthyes (bony fish), Family Salmonidae (salmon,
trout, and char), Genus Salmo (Atlantic salmon - salmo means jumper) and species Oncorhynchus (Pacific
salmon - 5 species; Oncorhynchus means "hooked snout").
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1. Do salmon hatch in salt water or fresh water?
__________________
2. After maturing enough to swim well, does the
young salmon swim upstream or downstream?
_______________________
3. What is the name of the area where a river meets
the sea (and where salmon undergo body changes
that let them live in salt water)?
_______________________________
4. Where do salmon live until they are mature and
ready to reproduce? ____________________
5. What sense do scientists think that salmon use to
return to their birthplace? _________________
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The life-cycle of this fish species is well
understood.
Larvae hatch from eggs, then develop into
juveniles. The juveniles then grow and
become adults, which then mature and spawn
to give rise to the next generation.
Spawning
 Adult cod form spawning aggregations from late winter to
spring.
 Females release their eggs in batches, and males compete to
fertilise them.
Pelagic Larval Phase
 Fertilised eggs drift with ocean currents and develop into larvae.
Adults
 Age of maturation varies between cod stocks, from ages 2 to 4 in
the west Atlantic, but as late as 8 years in the northeast arctic.
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Cod can live for 13 years or older, but as late as 8 years in the
northeast arctic.
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Spawning trout require a stream or river with a
gravel bottom that is free from silt. The female
digs a redd (egg nest) in the gravel by turning
onto her side and beating the gravel away with
her tail. In this depression or shallow hole, the
female will lay as many as 4 000 eggs. The male
will release milt on the eggs to fertilize them.
Trout do not stay to guard the eggs, but the
female will cover them by moving gravel onto
them with her tail.
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Depending on the species, trout eggs will
incubate from three to five months. As a
result of this long period, the eggs are
subject to disease and predation. The time of
incubation depends on the temperature of
the water flowing over the eggs. Generally the
warmer the water the faster the eggs develop.
However, temperatures above 10-15°C result
in water with lowered amounts of dissolved
oxygen, which may be fatal to the eggs.
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Eggs require oxygen-rich water owing to the
relatively thick membrane covering them.
Fast flowing water is ideal since the water
turbulence mixes oxygen into the water,
keeping the dissolved oxygen level high.
Warm or slow moving streams or lakes are
typically not good habitats for trout
spawning.
Eggs hatch in the gravel as alevins or sacfry. These are about 2.5 cm long with the
yolk sac still attached to them.
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Nutrients continue to be absorbed directly
into the blood from the yolk sac for about
10-20 days. During this time, alevins remain
hidden in the gravel as a protection from
predators.
After several weeks, they emerge as fry (5-10
cm) and begin to feed on plankton and bits of
free floating organic matter.
Upon reaching a length of 10-15 cm, trout
young are referred to as fingerlings