Module 18

Question 1

Properties of air and water

Answer 1

density:
- 800x less in air compared to water
viscosity:
- 50x less in air compared to water
oxygen concentration:
- 21% in air compared to 9% in water
diffusion:
- oxygen diffuses x1000000 faster than in water
compression:
- air can be compressed
- water cannot be compressed

Question 2

Undulatory propulsion - eel

Answer 2

muscle blocks known as myotomes on opposite sides of the vertebral column contract and relax in the eel body
- this generates waves that pass along the body from anterior where the side-to-side motion is small
- these waves travel too the posterior tail where the waves are greater in amplitude
- thrust is directed posteriorly and the eel moves forward

Question 3

Movement of fish in water

Answer 3

fishes use lateral waves of their bodies
- in combination with the movement of fins, thrust is generated to swim

Question 4

Drag force

Answer 4

resists the movement of a body in a fluid such as water or air
- organisms that want to move fast in a medium need to reduce drag
- because water is much denser than air, the effect of drag impeding locomotion occurs at much lower velocities
- on land, the speed at which we can easily walk at requires more energy if we want to achieve the same velocity in water

Question 5

Streamlined

Answer 5

animals that want to swim quickly need two have a streamlined body as this makes them hydrodynamic

Question 6

Slow-swimming fish

Answer 6

more interested in manoeuvrability than speed
- tend to have rounded bodies and large fins
- fins are highly articulated
- have finer control over the fin rays

Question 7

Drag

Answer 7

a mechanical force generated by the interaction and contraction of a solid body with a fluid

Question 8

Hydrodynamic

Answer 8

forces acting on by fluid

Question 9

Aerodynamic

Answer 9

forces acting on by air

Question 10

Thrust

Answer 10

a propulsive force

Question 11

Vortices

Answer 11

a whirling mass of fluid or air

Question 12

Buoyancy

Answer 12

the upward force exerted by a fluid that opposes the weight of a partially or fully immersed object
- density confers buoyancy in water
- reduces the burden of gravity

Question 13

Swim bladder

Answer 13

gas-filled sac found in most bony fishes
- reduces overall density, allowing it to become naturally buoyant
- adjusts how much gas is in the bladder
- positioned above the centre of gravity and immediately below the vertebral column –> this is so that the buoyant forces interacts with the fish’s mass to keep the fish upright and level
- oxygen is used as the gas to fill the swim bladder

Question 14

Why is oxygen used as the gas to fill the swim bladder?

Answer 14

oxygen is easily carried around the body from the gills
- using a counter currents system, the fish can dump oxygen into the swim-bladder as it descends
- as a fish ascends, it can take oxygen out of the swim bladder by reversing this process

Question 15

What happens as a fish goes deeper into water?

Answer 15

as a fish goes deeper into water it can decrease the volume of the swim bladder in response to the increase in pressure
- the fish must add more gas to achieve the same buoyant force

Question 16

What happens as a fish ascends?

Answer 16

as a fish swims up the water column pressure decreases
- the gas in the bladder expands
- if not controlled, the fish can come skyrocketing out of the water as the expansion rates increase

Question 17

Evolution of swim bladder

Answer 17

due to the nature of buoyancy, the swim bladder rapidly came to lie in a dorsal position in the visceral cavity

Question 18

Barotrauma

Answer 18

occurs when the swim bladder expands, forcing the stomach out through the mouth

Question 19

Shark buoyancy

Answer 19

sharks do not have a swim-bladder
- some sharks have become bottom-dwellers or developed large pectoral fins to provide lift
- some sharks have evolved oil livers too adjust their density
- some sharks gulp air into their stomach
the advantage of sharks not having a swim bladder is that they can rapidly change depth without worrying about bursting their swim bladder

Question 20

What sharks gulp air to provide lift?

Answer 20

whale sharks
basking sharks
grey nurse sharks

Question 21

Chondrichthyans

Answer 21

did not evolve to have a swim bladder and instead evolved to have a large liver containing a low-density oil called squalene
- this has a decreasing effect on overall density
- increases buoyancy

Question 22

Pectoral fins

Answer 22

lie close to the front of fish bodies
- can act as hydroplanes
- confer lift as the animal swims forward
- used in a few primate fish groups – few teleosts use pectoral fins this way

Question 22

Cookie-cutter shark

Answer 22

has two huge liver lobes that fill up most of the gut cavity
- sharks hang deep in water waiting for passing prey

Question 23

Pectoral fins in sharks and rays

Answer 23

sharks:
- act as hydroplanes
- sharks must either keep swimming or lie on the seabed because the are negatively buoyant
- the nature of the dynamic lift conferred by shark gyroplanes means that there are only a few options of their location on the body

rays:
- act as wings

Question 24

Neutrally buoyant bony fishes

Answer 24

not as constrained
- can use their pectoral fins in a surprising diversity of ways

Question 25

Caudal fins

Answer 25

• caudal fins of primitive actinopterygians are heterocercal
• this means they have unequal upper and lower lobes
• posterior end of the spine is bent slightly dorsally with an enlarged lower lobe of the connective tissue supported by rods of cartilage
• asymmetrical caudal fin generates some lift and asymmetrical thrust
  – this tends to drive the head forward as the fish swims
  – this force is countered by the low, large and anteriorly positioned pectoral fins of sharks and primitive actinopterygians

Question 26

Homocercal

Answer 26

symmetrical caudal fin
- found in teleosts where the posterior end of the spine is bent vertically at a right angle to the horizontal axis
- the fin rays now support a homocercal caudal fin
- this is a more derived from that generates symmetrical, posterior thrust

Question 27

Diphycercal

Answer 27

generates limited symmetrical, posterior thrust
- seen mainly in slow moving and deep-sea fishes

Question 28

Bodies of teleost fishes

Answer 28

diverse in terms of forms, shapes, and sizes

Question 29

Bodies of fast-swimming teleost fishes

Answer 29

body is spindle-shaped
- have a narrow caudal peduncle to reduce lateral forces as the tail sweeps backwards and forwards
- sickle-shaped tail is used to reduce the length over which water flows
– this also reduces drag as the fish swims forward

Question 30

What is important about the body shape of fast-swimming teleost fishes?

Answer 30

need to reduce drag, which increases quickly with speed due to the density and viscosity of water

Question 31

Body shapes of sharks

Answer 31

have fixed pectoral fins for lift

Question 32

Body shapes of pike and barracuda

Answer 32

rely on fast starts over short distances
- tend to have long bodies with a large caudal fin that is broad
- fin needs to generate maximum thrust to reduce drag

Question 33

Axial skeleton

Answer 33

caudal fin and undulations of the vertebral column

Question 34

Appendicular skeleton

Answer 34

pectoral and pelvic fins

Question 35

Locomotory challenge in the move onto land

Answer 35

main challenge was the low density and high compressibility of air
- no longer could thrust bee generated by thrashing of fins against the medium and no longer was the body supported by the buoyant force
- needed anatomical structures that could withstand the full force of gravity and provide thrust against the ground and air
- locomotion required more energy input and therefore more oxygen