The Yellow Perch
Written By: Zehra Nasirali
For: Mr. Sims
Course: SNC-2AI
Date: 20 November, 1997
Habitat:
The yellow
perch are usually found in the waters of Ontario and the northern part of U.S.
The yellow perch likes cool water. It
lives among the weed beds of shallow ponds, slow-moving streams or the margin
of lakes: it is here that it gets the food and protection it requires. However, during the warm summer it moves
deeper into the cooler water and when the cold weather returns, it surfaces.
Locomotion:
The perch’s
caudal fin (tail fin) helps it to move side to side and thus helps it to move
through water. It resembles the
propelling action of a boat’s motor.
The dorsal and anal fins help to keep the fish upright while the
pectoral and pelvic fins helps the fish to balance, to turn or stop and to
steer the direction. It resembles the
action in which the oars of a boat go.
The air bladder helps the fish to raise or lower itself. It contracts
and expands to alter the volume of air it contains. If its sac (air bladder) expands, the fish rises, as it is less
dense. If air is compressed, the fish’s density is increased and it sinks.
Body
The yellow perch has 2 distinct areas of color. Its dorsal surface (back) is olive green in color and its ventral
surface (underneath) is pale-cream in color.
It remains unnoticed if a predator swims above it because its dark
dorsal surface blends with the bottom of the dark sea. Likewise, the same happens if a predator
swims below it. It remains unnoticed
because its pale ventral surface blends with the sky. It also has bands of darker lines along the sides of its
body. This protects the perch because
the colors resemble the pattern of sunflecked reeds in the water.
The teeth
help in tearing the prey apart and holding it.
It doesn’t have teeth specialized to chew its food, therefore it has to
swallow its food as whole or in small pieces.
The perch’s
conspicuous eyes are only able to move slightly, it doesn’t have eyelids since
its eyes are constantly kept moist. It
has larger pupils than most vertebrates.
This means that they admit more light which is helpful for the perch to
see in semi-darkness. It cannot see
great distances when it is at rest, a distance of 15” approximately. Even though it can’t see great distances, it
picks up vibrations from the water to inform it of any approaching danger.
The
operculum is a body plate that is found on each side of the fish’s head. Each operculum forms a protective covering
for the underlying delicate gills.
You can
estimate the age of a perch by the number of lines on a scale.
The slime
that covers the fish’s body helps keeps out fungus diseases. It also helps the fish to move more readily
in water and to slip out from the grasp of an enemy.
The lateral
line is a set of scales on each side of the body that runs from between the
gills and the tail fin. Vibrations of
the sensitive organs indicate to the fish, by pressure changes, the level at
which it is swimming.
Breathing:
Gill rakers
are finger-like projections on the bony gill arch that points forward into the
mouth. These gill rakers act as
filtering devices that prevent debris from passing over the delicate filaments
and damaging them.
A gill is
composed of gill filaments. These
filaments are thin-wall projections containing blood vessels, which carry
deoxygenated blood close to their surfaces.
The exchange of gases from the water to the gills and vice versa, takes
place by simple diffusion. Carbon
dioxide enters the water from the gill filament and oxygen enters the gill
filament from the water.
Most fish can only survive a short time out of water. This is because they cannot use the oxygen in the air to breathe;
its oxygen must be obtained by diffusion from the water.
Digestive System:
The pylorus
is the conjunction of the stomach and small intestine. It regulates the passage of the partly
digested food from the stomach into the intestine.
The pyloric
caeca are 3 short sacs situated just beneath the pylorus. It is where the passage of food is delayed
to enable more chemical breakdown to take place.
Further
digestion takes place in the lower part of the small intestine. It is also where the nutritional part of the
food is absorbed through the intestinal wall and into the blood stream where it
is carried to all parts of the body.
The liver
produces bile to assist in the digestion of some fats. The bile is dumped into
the gallbladder and squirted into the small intestine to allow the bile to mix
with the passing food.
Excretory System:
The 2 brown
kidneys are organs of excretion. It
purifies the blood of the perch as it passes through them. Each kidney contains filtering units that
are capable of removing nitrogenous wastes.
The liver separates the protein from the nitrogen to allow the remaining
parts to be used for energy. After all
the nitrogenous wastes have been completely filtered, the nitrogen must be
eliminated. The urea (present state of
nitrogen) passes down to a urinary bladder and at intervals it is eliminated
from the urogenital aperture (behind the anus).
Circulatory System:
The perch’s
heart has 2 chambers: its shape is irregular and in it are one auricle and
ventricle. Deoxygenated blood from all
over the body collects in the burgundy colored auricle and passes to the
ventricle through a valve. The
ventricle contracts and forces the blood to the gill region to be
oxygenated. After being passed through
the body, the blood collects in the auricle once again as it has become
deoxygenated, and the cycle repeats.
Reproductive System:
It is
almost impossible to distinguish between the 2 sexes of the perch. However, the female is usually larger than
the male (because of her larger reproductive organs; eggs) if their age is the
same.
The roe is
a common name for the egg-mass, which is edible. To produce a perch, a female egg must be fused with a male
sperm. The process of fertilization is
external. When the water is warm, a
female will deposit her 100,000-approx eggs and cover it with a sticky coating
of mucus. After the eggs are laid, a
male perch deposits a milky fluid called milt, over the eggs in which the sperm
is contained. The laying of eggs and
fertilization is together called spawning.
After 3 weeks the small fish emerge and they look exactly like adults
only smaller in size. The fish live for
2 to 5 years but some live for 7 years.
They can reproduce at the end of its 2nd year of growth,
about 2 to 3 broods of fish in its lifetime.
Teachers
Comments: Well Done! 90%