Locomotion in Fish Flashcards

1
Q

Locomotory costs in water are relatively low but are affected by a number of factors, what are they?

A
  • Lift
  • Thrust
  • Weight
  • Drag
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2
Q

What does the heteroceral tail of shark do?

A

It causes an upward directed force posteriorly that rotates the body around the centre of mass.

(Tails of fast swimming sharks such as the Mako and Great white have a much more even shaped tail)

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3
Q

What are the 3 types of drag?

A

Pressure drag

Frictional drag (viscous drag)

Wave drag

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4
Q

Describe Pressure drag

A

The force required to overcome the inertia of the water molecules in in order to push them out of the way - varies with fluid density, velocity and the fish’s shape (streamlined or chunky)

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5
Q

Describe Frictional drag (viscous drag)

A

The boundary layer is a velocity gradient from the fish’s surface to the surrounding water - depends on fluid viscosity, surface area of the fish and velocity.

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6
Q

Describe wave drag

A

A fish swimming near the surface loses energy by making waves

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7
Q

Define viscosity

A

The viscosity of a fluid is the measure of its resistance to gradual deformation, sheer stress or densile stress. For liquids it corresponds to the informal concept of thickness. For example:

‘Honey has a higher viscosity than water’

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8
Q

What is the Reynolds number?

A

Density of the medium

x

velocity

x

linear dimension (length vs width)

/

viscosity of the water

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9
Q

What kind of animals tend to have the higher reynolds number?

A

larger animals have higher reynolds numbers because they are larger and faster.

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10
Q

Large animals such as birds, whales, dolphins are very well ‘what’ in order to reduce the ‘what’ on their body as they move through the medium

A

A. Streamlined

B. Drag

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11
Q

Low Reynolds numbers are associated with _______ flow

High Reynolds numbers are associated wuth _________ flow

A

A. Laminar (no turbulance)

B. Turbulent

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12
Q

The best body shape for encouraging laminar flow has a maximum thickness of around 0.25 of body length.

A
  • 0.25 of body length
  • depth & width of body approx 1/4 of total length.
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13
Q

Large fast swimmers cannot prevent drag by they can lessen its effects. How?

A

Surface compliance - instead of having a rigid body surface, soft and rubbery is better such as whale blubber allows the body to flex which dampens out turbulence.

Small projections - on the skin or scales create lots of small disruptions as apposed to big disruptions. Disrupts boundary layer which creates little turbulance instead of large (dimples on a golf ball, shark denticles)

Slime - (Mucus) reduces viscosity of the water in the boundary layer

(just 1% slime reduces friction by 60%)

Oscillation - of the fish’s tail pushes water back which helps to cancel the pressure drag in the fish’s wake.

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14
Q
A
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15
Q

Wake vortices by oscillatory swimming can assist schooling fishes which is why fish all swim slightly ______

A

A. offset

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16
Q

What are the two types of swimming in fishes?

A

-Undulatory (eels, rays)

Have high relative surface area (thin, flat or long bodies) increasing viscous drag, Slow swimmers but can swim backwards

-Oscillatory (Tuna, Mako)

Tail movement can only power you forward

17
Q
A
18
Q

The fastest swimmers have ____ bodies with hig ______ ratio tails

A

A. Stiff

B. Aspect

19
Q

High aspect fins have less ____ therefore less _____

A

A. Surface

B. Drag

20
Q

The aspect ratio is the span of the

A

span of the tail vs chord (thickness of the chord)

21
Q
A