P1252109107kDUoC

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Fishes 2 Teleostomes
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Teleostomes

• Think about life in water
• 3/4 of the earths surface is water (primarily
  ocean)
• Only 0.01 is freshwater.
• Freshwater is ephemeral compared to the oceans.
• Yet, 40 of all bony fishes live in fresh water.

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Getting Oxygen

• First Problem Getting oxygen.
• Use gills situated in pharyngeal pockets.
• Force water over the gills.
• Rely on concentration gradients to oxygenate the
  blood.
• Maximize O2 uptake by increasing flow rate of
  water, and forcing all water to go past a gill
  filament.

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Getting Oxygen

• Some fish do not rely on bucal pumps, instead
  they rely on ram ventilation. That is, they
  swim with open mouths (Tuna, sharks, mackerel,
  swordfish)
• Fish also rely on counter-current exchange system.

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Getting Oxygen

• Sometimes, there is insufficient oxygen in the
  water, and the gills are incapable of providing
  enough O2.
• Some fish are facultative air gulpers. In some
  species, the stomach is non-digestive at times,
  and functions as a secondary lung.
• Others (eels, some tropical fish, polypterus) are
  obligate air gulpers.

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Locomotion in water

• Basically, fish swim via lateral undulation.
• 3 basic forms of lateral undulation
• Anguilliform (fish can bend into more than 1/2 a
  sinusoidal wavelength)
• Carangiform (fish can bend into less than 1/2 a
  sinusoidal wavelength)
• Ostraciiform (inflexible body - undulation
  limited to caudal fin)

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Locomotion

• Maintaining position in the water column.
• For the most part, fish tissue is denser than
  water. Thus, fish tend to sink.
• This can be overcome in 2 ways
• Generate lift by swimming
• Use a swim bladder.

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Both birds and fish must overcome gravity and
drag, generate thrust, and control the body axis.
Since birds generate lift close to the central
moment, pitch is stable. However, thrust for the
fish is far from the central moment and thus the
fish has problems w/ yaw.
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Locomotion swim bladder.

• Gas filled swim bladder results in neutral
  buoyancy.
• Change in altitude in water column results in
  change in volume of bladder (because of change in
  pressure), and consequent loss of neutral
  buoyancy.
• Plesiomorphic solution to this is the pneumatic
  duct. These fish are physostomes, and gulp air.

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Locomotion swim bladder.

• Apomorphic solution is to use physoclistic
  approach. These use the gas gland (also found in
  physostomes) in conjunction with a rete mirabile,
  to excrete gas into the bladder.
• The gas gland releases lactic acid (acidic) which
  causes hemoglobin in the blood to release oxygen.
• An ovale sphincter is located at the dorsal
  posteior end to releave pressure.

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Locomotion generating thrust

• Thrust is generated by pushing against the water.
• Every time the fish pushes against the water,
  there is a reactive force which operates against
  it. Lateral undulation produces an active force
  directed backwards, and a lateral force. The
  overall reactive force is directed forward and to
  the side.

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Locomotion generating thrust

• Anguilliform and Carangiform fish increase speed
  by increasing the frequency of undulations (which
  transmits more power to the water).
• Longer fish have more induced drag, and thus are
  slower.
• Faster fish tend to be shorter. They also tend to
  be less flexible movement is transmitted to the
  caudal peduncle via ligaments. They also tend to
  have broader tails.

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Locomotion generating thrust

• Some fish oscillate only only the pectoral fins
  (reef fishes) Labriform locomotion.

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Locomotion minimizing drag

• There are 2 kinds of drag for a fish
• Viscous drag resulting from friction between the
  body and the water.
• This drag is relatively constant over the speeds
  exhibited by fish.
• Inertial drag resulting from pressure differences
  caused by displacement of water as the fish
  moves.
• This drag increases with increasing speed.

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Locomotion minimizing drag

• Viscous drag is dependent on surface
  characteristics - note, marine mammals are
  capable of near laminar flow.
• Inertial drag is dependent on body form.
• Fusiform shapes produce the lowest inertial
  drags. It is least when width is c. 25 of
  length, and this width is about 1/3 of the
  distance from the leading edge.
• If you are too thin, viscous drag increases
  because of relative increase in surface area.

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Locomotion minimizing drag

• Consider the shape of the tail caudal peduncle.
• Treat it just as you would treat a planes wings.
• There are both high aspect ratio wings and low
  aspect ratio wings. Substitute tails for wings.
  What kinds of tails would you associate with
  different swimming modes?

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Sensory systems in water Light.

• Light does not penetrate very far into the water
  column.
• Focusing light depends on the different
  refractive properties of fluids (air is a fluid).
• For fish, the difference in refractive properties
  of water and the interoccular fluid is too slight
  to accomplish much bending of light.
• Consequently, fish rely on changing the position
  of the lens relative to the retina to focus.
  (note- whales do this too)

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Sensory systems in water chemicals

• Fish have taste buds and olfactory organs in
  the mouth, on the surface of the head, and on the
  anterior fins.

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Sensory systems in water Mechanoreceptors

• These detect displacement
• Touch, sound, pressure, and motion.
• Also possess a labyrinth organ, with homologies
  to the inner ear of terrestrial vertebrates.
• Note, fish have the ability to tell up from down
  - you can fool a shark.
• Lateral line system

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Sensory systems in water Lateral line

• Neuromast organs on the head, and on one or more
  lines along the side of the body, all the way to
  the tail. This is also found in aquatic
  amphibians.
• Lateral line
• neuromasts in 2 configurations.
• Within tubular canals.
• Exposed in epidermal depressions.

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Sensory systems in water Lateral line

• Neuromast organs are based on hair cells.
• Hair cells have asymmetric kinocilia in a
  microvilli.
• These hair cells are arranged in pairs, with the
  kinocilia on opposite sides of adjacent cells.
• Each neuromast has 2 afferent nerves one carries
  impulses from kinocilia in one orientation, the
  other from kinocilia in the opposite orientation.

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Sensory systems in water Lateral line

• The microvilli and kinocilia are embedded in
  gelatinous cupola. Deformation of the cupola will
  either excite or inhibit the neuromasts nervous
  discharge.
• Thus, the system is sensitive to direction of
  displacement.

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Neuromast organs in the killifish. Note the
overlapping perceptual fields of the groups of
organs.
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Electroreception and Electric Discharge
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