Transcript Evolution of the Modern Fish

Evolution of the Modern Fish
·Fish were the first vertebrates to evolve.
·First fish were jawless creatures whose bodies were armored with bony plates
·Evolution of jaws and paired fins were major adaptations
·Jaws allowed for varied eating
·Paired fins allowed for better control of movement.
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Fish are aquatic vertebrates that are characterized by:
·paired fins
·scales
·gills
Form and Function in Fish
Adaptations needed for aquatic life include:
·various modes of feeding
·specialized structures for gas exchange
·paired fins for locomotion
·buoyancy equilibrium (don't sink and don't float to the top!)
Feeding!
Every mode of feeding is seen in fishes:
·herbivores (Clown Surgeonfish)
·carnivores (barracuda)
·parasites (lamprey)
·filter feeders (Atlantic menhaden)
·detritus feeding (catfish)
Respiration and Circulation:
http://www.marinebiology.org/fish.htm#How%20Fish%20Breath
·water surrounding a fish contains a small percentage of dissolved oxygen.
·fish must use a special system for concentrating the oxygen in the water to meet their physiological needs.
·closed circulatory system, i.e. blood travels across the body through the network of blood vessels.
·Unlike humans, fish exhibit single cycle circulation, where the oxygen deprived blood comes to the heart, from whe
is pumped to the gills and then circulated to the entire body. On the other hand, in mammals, the deoxygenated bloo
enters the heart, from where it is pumped into the lungs for oxygenation. Then, the oxygenated blood returns to the
from the lungs, to be transported throughout the body.
·Water enters the mouth by a pumping system that involves the mouth and the outer flexible bony flap that
cover the gills called the operculum. When the fish’s mouth is open, the operculum closes and water is drawn
into the fish’s mouth. Conversely, when the fish closes its mouth, the operculum opens and fresh water is then
allowed to flow across the gills.
·After water enters the fish's mouth it passes through a structure called the gill rakers. The function of the gill
rakers is to act as a filter system.
·The filtered water then travel through the gill arches thus passing over the gills. Each gill consists of two rows of
extremely thin membranes called gill filaments. The structure of the gill filaments consist of a capillary network
called lamellae. Gill filaments which are projected out into the water flow allows water to flow across the lamellae.
This will result in gas exchange where, oxygen and carbon dioxide are exchanged directly across the capillary
membrane.
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Always Exceptions:
African Lung Fish
http://animal.discovery.com/videos/river-monsters-belching-african-lungfish.html
Movement
The density of water makes it very difficult to move in, but fish can move very smoothly and quickly.
A swimming fish is relying on its skeleton for framework, its muscles for power, and its fins for thrust and direction.
The skeleton of a fish is the most complex in all vertebrates. The skull acts as a fulcrum, the relatively stable part of the
fish. The vertebral column acts as levers that operate for the movement of the fish.
The muscles provide the power for swimming and constitute up to 80% of the fish itself. The muscles are arranged in
multiple directions (myomeres) that allow the fish to move in any direction. A sinusoidal wave passes down from the
head to the tail. The fins provide a platform to exert the thrust from the muscles onto the water.
Drag
Drag is minimized by the streamlined shape of the fish and a special slime fishes excrete from
their skin that minimizes frictional drag and maintains laminar (smooth) flow of water past the fish.
When Thrust > Drag,
we have swimming!
Fins- fins give a fish control over its movements by directing thrust, supplying lift and even acting as brakes. A fish must
control its pitch, yaw, and roll.
Caudal fin-- provides thrust, and control the fishes direction
Pectorals-- act mostly as rudders and hydroplanes to control yaw and pitch. Also act as very important brakes by
causing drag.
Pelvic fins-- mostly controls pitch
Dorsal/anal-- control roll
Swim Bladders
Bony fish have swim bladders to help them maintain buoyancy in the water. The swim bladder is a sac inside the
abdomen that contains gas. This sac may be open or closed to the gut. If you have ever caught a fish and wondered
why its eyes are bulging out of its head, it is because the air in the swim bladder has expanded and is pushing against
the back of the eye. Oxygen is the largest percentage of gas in the bladder; nitrogen and carbon dioxide also fill in
passively.