Biology 201Dr. Edwin DeMont

St. Francis Xavier University

The Fishes: Vertebrate Success in Water

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The Fishes

The locomotor structure of a fish

functions to propel it through the water and

helps to reduce the cost of locomotion.

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No Slip Condition

No flow exists at the interface of a solid and a

moving fluid.

Filmed live

Surface of fish or Wall of artery

Velocity gradientShear forces

FrictionBoundary layer (b.l.)

Video

Skin Friction Drag

Always exists

Laminar or turbulent

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Drag Reduction

Aquatic swimmers have several different mechanisms to reduce skin friction drag.

- Riblets on scallops

- Fish Slime

- Riblets on sharks

- Modify b.l. Laminar ↔ turbulent

Human swimmers

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Pressure drag

Filmed live

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Low pressureHigh pressure

Pressure Drag

Pressure differences create a pressure gradient → Pressure Drag

Reduce pressure drag by

streamlining.

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Total drag

Total Drag = Skin Friction Drag + Pressure Drag

Total Drag → constant × V2

Drag on body slows it down – wastes energy

But – drag isn’t always bad news…

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Drag as thrust

Fins oscillate back and forth creating drag on the fin.

What happens on the forward (recovery)

stroke?

During the backstroke (power) the drag force is

directly forward and becomes the thrust force.

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Whole Body

Whole body (or caudal fin) undulations also generate thrust.

Tail interacts with water to form

‘vortexes’ that move downstream and ‘push’ the fish

forward.

Volume of s.b. decreases

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Buoyancy Control

Several mechanisms aid in vertical regulation and

include fins to create lift, changing body density by the

addition of oils.

Swim bladders (s.b.) are also used for

buoyancy.

Water pressure increases

Density of fish increasesNeed to precisely control

volume. Why?

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Buoyancy Control

Two types of swim bladder: (1) no connection to gut and (2) direct connection to gut.

2. Physostomous fishes 1. Physoclistous fishesAnother diagram

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Countercurrent Multiplier

Swimbladder

Gas gland

Normal blood flow through rete

O2

O2

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Countercurrent Multiplier

Swimbladder

Gas gland

Fish wants to move oxygen into Swimbladder

Produces lactic acid

O2 O2

O2

O2

Decreases affinity of oxygen to hemoglobin

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Countercurrent Multiplier

Swimbladder

Gas gland

Fish wants to move Oxygen into Swimbladder

Produces lactic acid

O2 O2

O2 O2O2

O2O2

O2

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Countercurrent Multiplier

Swimbladder

Gas gland

Fish wants to move Oxygen into Swimbladder

Produces lactic acid

O2 O2

O2 O2O2

O2O2

O2 O2O2

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Countercurrent Multiplier

Swimbladder

Fish wants to move Oxygen into Swimbladder

O2 O2

O2 O2O2

O2O2

O2 O2

O2

O2

O2

O2

O2 O2

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Sensory FunctionsP

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Sensory receptors are widely distributed and used for

olfaction, vision, hearing, equilibrium and for detecting

water movements.

Schooling may be controlled by sensing water movement

generated by nearby fish.

Collision-free Driving by Mimicking Fish Behavior

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Lateral Line

The lateral line system is a set of pits that detect

changes in water pressure.

Why is the lateral line located here?

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Shear forces in b.l. bend cupula

Sense hairs bend and response initiated.

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Sound Production

Audio communication is not obvious in fishes, but may be used extensively.

Low frequency sounds can be detected by lateral line

receptors.White Grunt (Haemulon

plumieri)

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Atlantic HerringP

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‘Frt’ing Sound (at night)

ContactAnti-predator

(Fast Repetitive Tick)

Communication:- Reduced lateral line

- Swim bladder connects to inner ear and gut.

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DVD Video

Wild Moves: Insights into Animal Physiology

Fish and Marine Mammals:Swimming and Diving

Several questions will be raised during the video. By the end of the video, you should be able to answer the questions listed on the next slide.

www.films.com

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DVD Video

1. What determines the locomotor styles of fishes?

2. How do fish change their locomotor style with speed?

3. Why do fish have two types of muscles?

4. Why do large fish swim the fastest?

5. What mechanisms do aquatic animals use to maintain themselves in the water column?