Movement in water

Aim floating or sinking jet propulsion swimming

slow fast

mechanics and shape of an optimal design

how fish move forwards

References Schmidt - Nielsen K (1997) Animal

physiology McNeill Alexander R (1995) CD Rom

How Animals move Web links: see:http://biolpc22.york.ac.uk/632/movelectures/

water/

In water density of flesh similar to that of water

Skeletal support not so important Swimming more efficient than running!

major cooling effect

density = mass / volume air 1 kg /m3 distilled water 1000 kg / m3

sea water 1030 kg / m3

but tissues denser than water muscle 1060 kg / m3

bone 1500-2000 kg / m3

Floating density of fish > water less dense than water

jellyfish : jelly shark liver : squalene

swim to generate lift sharks

gas store Physalia Nautilus oxygen teleost swimbladder

Sharks have to swim… lift from aerofoil shape of pectoral fins

asymmetric tail moves more water on top forces water down and shark up

Floating with CO Physalia

makes carbon monoxide

Floating with gas Nautilus oxygen rigid chamber

x-ray mostly gas last still water filled

Swimbladders full of oxygen X-ray of butterfly fish

Swimbladders at depth Pressure increases with

depth 1 atm = 10 m Swimbladders get

smaller, give less buoyancy

fish unstable with depth

How fill swimbladder1. secrete lactic acid into blood

forces hb to release O2 [Root effect]

2. run a counter-current exchanger keep O2 in blood of rete mirabile

Blood flow in rete

flow

lactic acid

Oxygen flow in rete counter current

can fill swimbladder at 100 atm

bladder

Summary so far buoyancy can be solved

low density active gas secretion swimming

carry a cost larger (more drag from wider body) difficult to stay stable

what is the optimal solution?

Jet propulsion conservation of momentum = m*v mass of fish * velocity of fish

= mass of water * velocity of water squid

contract mantle dragonfly larvae

Paddling / rowing ducks beetle larvae frogs swimming

Paddling / rowing depends on conservation of

momentum ducks beetle larvae frogs swimming

Drag

Reynolds number gives an estimate of drag Re = length * speed * density / viscosity

for air, density / viscosity = 7*104 s / m2

for water; density/ viscosity = 106 s/m2

friction

turbulence

Reynolds number Re < 1 no wake

e.g. protozoan Re < 106 flow is

laminar e.g. beetle

Re > 106 flow is turbulent e.g. dolphin

Drag depends on shape Drag reduced by up to

65% by mucus

Swimming Undulations

side to side (fish) up down (whales, dolphins)

how do undulations propel you forwards?

Rowing fins (reef fish) legs (insects e.g. beetle larvae & birds)

How does a fish move?

How are swimming movements produced?

Myomere arrangement

Myomere cross-section White muscle contracts anaerobically,

using glucose for fuel and producing lactate.

Red muscle contracts aerobically, using lipid for fuel and producing CO2.

Design for minimal drag

tuna or swordfish: highly efficient for high-speed cruising

in calm water torpedo-shaped body narrow caudal

peduncle lunate, rigid

fins

Why don't all fish look like that?

The design is highly inefficient: In naturally turbulent water (streams,

tidal rips, etc.) for acceleration from stationary for turning for moving slowly & especially for lying still

Size and shape

easy to turn - rigidslow - fast

head moves - head stillpower from whole - power from tail

muscles pull via tendons on tail fin

Ambush predators keep head still

long body/dorsal fins rapid start

flexible body, plenty of muscle large tail fin

barracuda pike

Design for manoeuvrability

Small items don't move fast, but require delicate, focused movements for capture.

A short, rounded body with sculling or undulating fins.

Compressing the body laterally provides a wide surface to exert force on the water

Optimal design? No one optimal design efficient energetics isn’t all maximum speed isn’t all

How is thrust generated?

thrust = momentum / time anguilliform

How else is thrust generated?

tail movement Carangiform

tail generates symmetric vortex street

noterotation

How else is thrust generated?

tail movement acts like a hydrofoil thunniform cetaceans penguins

Flying not swimming tail movement acts like a hydrofoil generates lift and drag

drag acts in line of motion lift acts perpendicular (normal) to drag

draglifttotal

Summary gravity less important buoyancy can be solved thrust from

paddles [fins] body tail

no one optimal solution?

point to ponder: swimming in protozoa